HOUSE No. 2260 Cf)e Commontoealtl) of QiaosacJmgetts! SPECIAL REPORT OF THE DEPARTMENT OF PUBLIC HEALTH RELATIVE TO VARIETIES AND PREVALENCE OF MOSQUITOES IN THE COMMONWEALTH Under Chapter 14 of the Resolves of 1939 December, 1940 BOSTON WRIGHT & POTTER PRINTING CO., LEGISLATIVE PRINTERS 32 DERNE STREET 1941 CONTENTS. PAGE Report of the Department of Public Health 5 Financial Statement 12 Report of the Director of the Division of Communicable Diseases ... 13 Equine Encephalomyelitis 14 Varieties of Equine Encephalomyelitis 14 Other Methods of Transmission 16 Possible Reservoirs of the Disease 17 The Massachusetts Outbreak of Equine Encephalomyelitis . . . .18 Epidemiology 18 Other Mosquito-Borne Diseases 22 Diseases with Proved Mosquito Transmission 23 Diseases with Suspected Mosquito Transmission 24 The Control of Mosquito-Borne Diseases 24 Personnel and Methods 26 Collections Per Square Mile 29 Influence of Meteorological Conditions on Mosquitoes 31 Rain 31 Temperature 33 Wind 33 Mosquito Breeding Places 34 The Collection of Adult Mosquitoes 38 Biting Habits 38 Environment 42 Vectors of Equine Encephalomyelitis 45 Numerical Importance of Vectors 45 Biting Habits 49 Vectors of Malaria 50 Numerical Importance 50 Biting Habits 52 Mosquitoes of Massachusetts 52 Genera 52 Seasonal Distribution 64 Species 56 Public Health Importance of Aedes Species 63 Aedes atropalpus 63 Aedes aurifer 63 Aedes canadensis 64 Aedes cantator 64 Aedes cinereus . . 64 Aedes communis 65 Aedes dorsalis 65 Aedes excrucians 65 Aedes fitchii 66 Aedes hirsuteron 66 Aedes impiger 66 4 CONTENTS. Public Health Importance of Aedes Species Con. page Aedes implacabilis 66 Aedes intrudens 66 Aedes punctor 66 Aedes sollicitans 67 Aedes stimulans 67 Aedes taeniorhynchus 67 Aedes trichurus 68 Aedes triseriatus 68 Aedes trivittatus 68 Aedes vexans 68 Summary and Conclusions 69 Tables. No. I. Mosquitoes Known to Transmit Equine Encephalomyelitis to Labo- ratory Animals 16 11. Diseases with Proved and Suspected Mosquito Transmission in the United States 22 111. Summary of Mosquito Collections, 1939 28 IV. Mosquito Collections Adults, Larvae and Per Cent Distribution, by Weeks 29 V. Direction of Prevailing Winds 33 VI. Mosquito Breeding Places at Regular Collection Points . . .34 VII. Association of Larvae at Collection Points 36 VIII. Adult Mosquitoes Caught on Man 39 IX. Adult Mosquitoes Caught in Houses 40 X. Adult Mosquitoes Caught on Man and in Houses . . . .41 XI. Adult Mosquitoes Caught in Barn and Stable 42 XII. Association of Vector Adults with Different Types of Terrain . . 44 XIII. Numerical Importance of Vectors of Equine Encephalomyelitis, by Specimens 45 XIV. Numerical Importance of Vectors by Counties 47 XV. Vectors of Equine Encephalomyelitis Per Cent of Adult Specimens which were Vectors 48 XVI. Vectors of Malaria Distribution of Species by Counties . . .51 XVII. Relative Importance of the Genera of Massachusetts Mosquitoes Per Cent of Adults and Larvae by Specimens 53 XVIII. Average Number of Specimens Per Collection 54 XIX. Summary of Mosquitoes of Massachusetts 57 XX. Mosquitoes of Massachusetts by Counties 59 Map and Graphs. Map I. Distribution of Equine Encephalomyelitis . . . . . 19 Graph I. Seasonal Incidence of Equine Encephalomyelitis . . . .21 Graph 11. Precipitation 32 Graph 111. Seasonal Prevalence of Genera 55 Cf)t Commontoealtf) of QiasgaciHigetts SPECIAL REPORT OF THE DEPARTMENT OF PUBLIC HEALTH RELATIVE TO VARIETIES AND PREVALENCE OF MOSQUITOES IN THE COMMONWEALTH. [Public Health.] To the General Court of Massachusetts. December 4, 1940. In accordance with the authority delegated to it, the Department of Public Health, in co-operation with the Federal Work Projects Administration, has investigated the prevalence and the seasonal and geographical distribu- tion of mosquitoes throughout the Commonwealth as pro- vided by chapter 14 of the Resolves of 1939. This resolve is as follows: Resolved, That the department of public health is hereby authorized to investigate, in co-operation with the Federal Work Projects Administra- tion or its successor, the prevalence and the seasonal and geographical distribution of mosquitoes throughout the commonwealth. For said pur- pose said department may expend for services, other than services of said Federal Work Projects Administration or its successor, and for traveling expenses, supplies, materials and equipment, a sum not exceeding seven- teen thousand five hundred dollars, which sum is hereby appropriated from the General Fund or ordinary revenue of the commonwealth in advance of final action on the general appropriation bill, pursuant to a recommen- dation of the governor to that effect. Said department shall report its recommendations, if any, together with drafts of legislation necessary to carry such recommendations into effect, by filing the same with the clerk of the house of representatives on or before the first Wednesday of Decem- ber in the year nineteen hundred and forty. This resolve was passed and the funds made available in response to a request from His Excellency the Governor in a special message to the General Court dated April 12, 1939, in which reference was made to an epidemic of en- 6 HOUSE— No. 2260. [Jan. cephalomyelitis (horse sleeping sickness) in certain parts of the Commonwealth which was believed to have been the source of encephalitis in humans. In that message to the Legislature it was pointed out that this disease is extremely dangerous to young people, and that there is a considerable fear among health authorities that there may be a recur- rence of the epidemic. Chapter 14 of the Resolves of 1939 was approved on May 9, 1939. During the summer of 1938 there were 269 deaths from encephalomyelitis in horses, and 34 cases of encephalitis with 24 deaths among humans. This was the first time that the disease in humans was recognized as having been caused by the virus of encephalomyelitis of horses. While this disease was extremely prevalent in the summer of 1938, there were only 12 suspicious cases in horses in the summer of 1939 and only 8 in 1940, of which only 2 in 1939 and none in 1940 were proven. There was only 1 suspicious human case in 1939, while none have thus far been reported in 1940. Following the epidemic of encephalomyelitis in 1938 the Department, at its meeting on October 11, 1938, acting under the provisions of section 6 of chapter 111 of the Gen- eral Laws, as amended by chapter 265 of the Acts of 1938, changed the list of diseases declared dangerous to the pub- lic health by the removal of “Encephalitis Lethargica,” as it then appeared, and substituting in place thereof the term “Infectious Encephalitis,” and the Department also pro- vided that the minimum period of quarantine of the patient be one week after the onset of the disease in an insect-free room. While as complete an investigation as was practicable was made in 1939 of the prevalence and geographical dis- tribution of mosquitoes throughout the Commonwealth, conditions during the investigation were unfortunate be- cause the year 1939 was one of low rainfall and consequently one when mosquitoes were less prevalent than during the epidemic of 1938 and during years of normal rainfall. Dur- ing the year 1938 there was an excess of about 11.7 inches 1941.] HOUSE— No. 2260. 7 of rainfall above the normal throughout the State as a whole, or an excess of 26 per cent, while in 1939 there was a deficiency of some 5.5 inches of rainfall, or 13 per cent below the normal. With the co-operation of the Work Projects Adminis- tration, and with the use of certain rooms and consulting services of Harvard University, over 23,000 specimens of adult, biting mosquitoes were collected and over 249,000 specimens of larvae were collected. All of these specimens have been examined by entomologists and identified by species. Fifty-six different species of mosquitoes were col- lected, and of these, investigations have shown that six are known vectors of encephalomyelitis in animals. Of the various mosquitoes and larvae collected, 22.1 per cent of the adult mosquitoes and 2.9 per cent of the larvae were determined to have been of the species capable of trans- mitting this disease. Collections were made in all but two of the municipalities of the Commonwealth, and from those collections the distribution of the species capable of trans- mitting the disease was determined. One species, Aedes vexans, was found in practically every municipality in the State. The collections cannot be considered in any way an exact numerical measure of the prevalence of mosquitoes in any given portion of the State, but they do show where the different species are found. A definite numerical determi- nation of the prevalence of mosquitoes would be impracti- cable. The number of collections varied more in accord- ance with the interest and ability of the personnel engaged in the investigation than with the actual number of mos- quitoes and larvae present in a given territory. Compara- tively few collections were made in Suffolk and Hampshire counties. Large collections were made in Middlesex, Worces- ter, Berkshire, Plymouth and Essex counties. A very con- siderable number of mosquitoes were collected in Barnstable County and on the islands of Martha’s Vineyard and Nan- tucket, where rather complete work in mosquito control has been carried on under the direction of the State Reclama- 8 HOUSE —No. 2260. [Jan. tion Board, the results of which have been to enhance the real estate and recreational values of these regions. Some mosquito collections were made by the Depart- ment’s representatives, beginning the week of April 22, 1939, before the resolve was passed, but these collections were small in number and large scale collections were not started on a state-wide basis until the first week in July. They were continued through October, only scattered col- lections in certain areas being made thereafter. There was a very marked falling off in collections during the last week in October. The maximum collections of larvae occurred during the week ending October 7, while the maximum col- lections of adults occurred during the week ending Septem- ber 23. Following the week ending July 15 there was a falling off in the collections of adult mosquitoes, but an in- crease in the collections of larvae, due to more favorable breeding conditions. The investigation has shown that mosquitoes of the vari- eties known to transmit sleeping sickness are less likely to be found in barns or houses than are other species. A large proportion of the known vectors of this disease were found in the vicinity of swamps and standing water and in wooded areas. It may be concluded from this investigation that in times when there is danger of the occurrence of encephalomye- litis, children and adults should avoid swamps and wooded areas, and very young children should be kept in screened houses or other enclosures where they cannot be reached by mosquitoes. During such periods horses should be kept in barns rather than in the open. A very considerable amount of information has been ob- tained through the investigation, under the provisions of chapter 14 of the Resolves of 1939, by both the Depart- ment of Public Health and the Work Projects Administra- tion, relative to Massachusetts mosquitoes, and numerous reports have been mimeographed and distributed. It is impracticable to condense all of this information in a legis- lative report, but a considerable number of mimeographed 1941.] HOUSE No. 2260. 9 documents are available in the office of the Department of Public Health for distribution to members of the Legisla- ture and others upon request. Under the provisions of chapters 112 and 465 of the Acts of 1931, chapter 307 of the Acts of 1932, and chapters 89 and 371 of the Acts of 1933, a total of $600,000 was appro- priated by the Legislature to provide for the employment of persons in carrying out mosquito control projects under the direction of the State Reclamation Board, and under these appropriations a very considerable degree of mosquito control of the salt marsh species has been effected. These salt marsh species are among the six vectors found to be capable of spreading the virus of encephalomyelitis, and this control work may be the reason why the disease was less prevalent in the coastal areas in Massachusetts in 1938 than it would have been if the control work had not been carried out. However, very little work has been done by the State in mosquito control in fresh-water areas, as the work in such areas involves a greater variety of control problems than does the salt marsh work. The fresh-water varieties of mosquitoes generally do not migrate to such great distances as the salt marsh varieties. The recent epidemic of encephalomyelitis in Massachu- setts started in West Bridgewater, and a considerable num- ber of the cases occurred in the Taunton River Basin. About 70 per cent of the cases among horses occurred in a thirty-mile square extending from the mouth of the Taun- ton River in the south, to Boston in the north, and from the boundary of Rhode Island northeasterly to the coast line. The human cases were rather widely distributed in Plym- outh, Middlesex, Norfolk and Bristol counties, with six cases in Boston. The first cases in humans were in Brock- ton and Bridgewater. The municipalities in which about two thirds of the human cases occurred are known to contain swamp or marsh areas. The area referred to above includes a large variety of mosquito breeding places, among which is the large Hockamock or Great Cedar Swamp in 10 HOUSE —No. 2260. [Jan. Bridgewater, Easton, Raynham, Taunton and West Bridge- water, This swamp is located not far from the middle of the territory in which the bulk of the cases in horses oc- curred. It covers an area of more than 7,000 acres and is the largest fresh-water swamp in the State. There has been considerable interest from time to time in the drainage of this swamp, in the reclamation of the land, and in the pos- sibility of the establishment of a huge bird sanctuary. Col- lections of all of the known vectors of the disease were made in this area. Drainage of this swamp should be more ade- quately controlled. In view of the evidence that encephalomyelitis may be spread by mosquitoes, and in view of the natural objection to mosquitoes, the Department is of the opinion that more adequate facilities should be provided for draining inland swamps and marshlands, thus extending the control over the species of mosquitoes capable of spreading this disease and of the mosquito pest in general. Mosquito control facilities should be made available in all known mosquito breeding areas throughout the State as a whole. Such a program can be accomplished in two ways, viz.: 1. By the State Reclamation Board, through special acts of the Legislature. 2. By local projects organized under chapter 252 of the General Laws, as amended. The Department is of the opinion that any drainage works for mosquito control measures, including studies re- lating thereto, should be carried out by the State Reclama- tion Board, organized under General Laws, chapter 252. It is recognized that complete mosquito control is im- practical, and no further definite legislation is recommended by the Department in connection with its investigations under the provisions of chapter 14 of the Resolves of 1939, but with the approval of the State Reclamation Board suit- able legislation and funds might well be provided to per- mit that Board to carry on effective drainage of inland swamp and marsh areas, to apply larvicides, and to use other means for more adequate mosquito control in fresh- water areas, with a view primarily to preventing the further 1941.] HOUSE— No. 2260. 11 distribution of encephalitis. A basis of such legislation can be found in chapter 655 of the Acts of 1911 relative to the protection of the public health in the valley of the Nepon- set River, which provided for the dredging and deepening of the channel of that stream, and which provided for the construction of drains, trenches and ditches in the adjacent meadows. Respectfully submitted, PAUL J. JAKMAUH, M.D., Commissioner of Public Health. RICHARD P. STRONG, M.D. JAMES L. TIGHE. GORDON M. HUTCHINS. R. NELSON HATT, M.D. RICHARD M. SMITH, M.D. FRANCIS H. LALLY, M.D. 12 HOUSE No. 2260. [Jan. FINANCIAL STATEMENT. Appropriation 517,500 00 Expenditures: Personal services 54,818 09 Travel 9,048 81 Equipment and supplies . . . . 1,561 95 Rental of furniture and other equipment . 771 13 Stationery and office supplies . . . 517 40 Express, postage, telephone, etc. . . 477 81 Books, maps, printing, etc 266 07 Drafting supplies 33 98 Total expenditure 17,495 24 Balance $4 76 1941.] HOUSE —No. 2260 13 REPORT OF THE DIRECTOR OF THE DIVISION OF COMMUNICABLE DISEASES OF THE DE- PARTMENT OF PUBLIC HEALTH RELATIVE TO THE PREVALENCE AND THE SEASONAL AND GEOGRAPHICAL DISTRIBUTION OF MOSQUITOES IN THE COMMONWEALTH. To Dr. Paul J. Jakmauh, Commissioner of Public Health. November 1, 1940. Dear Sir : Herewith is submitted a report relative to investigations made by the Department of Public Health in co-operation with the Federal Work Projects Adminis- tration, as authorized under the provisions of chapter 14 of the Resolves of 1939, relative to the prevalence and the seasonal and geographical distribution of mosquitoes throughout the Commonwealth. The resolve was passed and funds made available in response to the request of his Excellency the Governor, which reads as follows (House, No. 2181): The Commonwealth of Massachusetts, Executive Department, State House, Boston, April 12, 1939. To the Honorable Senate and House of Representatives. House Bill No. 399, a resolve providing for an investigation by the Department of Public Health, in co-operation with the Federal Works Progress Administration, relative to the varieties and prevalence of cer- tain kinds of mosquitoes in the Commonwealth of Massachusetts, calls for an appropriation in the aggregate of $17,500. This sum will be the Commonwealth’s contribution to the cost of the investigation, and will permit the Department of Public Health to investigate, in co-operation with the Federal Works Progress Administration, the prevalence and the seasonal and geographical distribution of mosquitoes throughout the Commonweal th. Last summer there was an epidemic of encephalomyelitis in certain parts of our Commonwealth. This is an extremely dangerous disease to young people, and there is considerable fear among the authorities that 14 HOUSE No. 2260. [Jan. there may be a recurrence of this epidemic in the coming summer months. Work with relation to mosquitoes, to be effective, must be done in the month of May. I therefore recommend this appropriation to be made in advance of the budget. Leverett Saltonstall, Governor of the Commonwealth. Equine Encephalomyelitis. The Mosquito Survey was organized as a result of the 1938 outbreak of horse-sleeping sickness (equine encepha- lomyelitis) among humans, animals and birds in south- eastern Massachusetts. This was the first time that the disease was recognized in this State; moreover, it was the first time that equine encephalomyelitis was demonstrated to infect species other than horses and mules. Equine en- cephalomyelitis is a newly recognized infectious virus dis- ease. Its economic importance is great, as it kills thousands of horses and mules every year and is now known to be fatal in humans. Laboratory experiments have demon- strated that many species of small mammals and birds are susceptible. With its recognition among humans, the dis- ease has become a problem which requires study to arrive at some method of control. The mosquito has been proved experimentally to be able to transmit the disease, and there is much evidence that certain species are the natural vectors. The objectives of the Mosquito Survey were: to collect and determine the various species of mosquitoes present in Massachusetts; to obtain data on the geographical distri- bution and the seasonal predominance of the different species; and to ascertain the possible relationship of such mosquitoes to certain diseases which are transmitted by these insects. Varieties of Equine Encephalomyelitis. Equine encephalomyelitis is a disease which may be due to one of four different varieties of virus. The clinical pic- ture produced by each variety ranges from a mild and sub- acute form to one which is fulminating and acute. Similarly,. 1941.] HOUSE —No. 2260. 15 the varieties may be separated by well-recognized labora- tory methods. In the United States only the western and eastern varie- ties are known to occur. The western is limited to the area west of the Appalachian Mountains; epizootics of this variety among horses have been characterized by a high attack rate, a low fatality rate, and a subacute form of this disease. The eastern variety, on the other hand, has been known to occur only along the Atlantic seaboard. In 1939 both the eastern and western varieties were reported from Alabama. Epizootics of the eastern variety are character- ized by a low attack rate, a high rate, and a more acute and fulminating type of disease. Both varieties have been demonstrated to affect humans. However, because only a few cases of the disease have been recognized, it is impossible to describe exactly the characteristics of infec- tion in man with these viruses. Nevertheless, with the in- formation on hand, it seems likely that the western variety of this disease in man may be in many instances subclinical or mild, whereas the eastern variety causes an acute and fulminating type of disease not unlike that in horses. Many investigators have experimented with the mosquito trans- mission of this disease. At first, these experiments were difficult to interpret, due to the varying conditions under which they were performed. At the present time there are seven species of mosquitoes which have been demonstrated experimentally to transmit the eastern virus to laboratory animals. Two of these carriers were added to the list in 1939 by a worker at the Harvard Medical school, using material supplied by the survey. The western virus has been transmitted by eight species of mosquitoes. In all instances of transmission, the mosquito concerned belonged to the genus Aedes. Transmission experiments with the other genera of mosquitoes, Culex, Anopheles, Theohaldia, Mansonia, Wyeomyia and Uranotaenia, have thus far been negative. Table I gives a summary of the transmission experiments. It is apparent that some mosquitoes have been shown to transmit one variety of the virus, but not the other. So 16 HOUSE No. 2260. [Jan. far as is known, there is no biological reason why any species of mosquitoes should be able to transmit one variety of equine encephalomyelitis virus and not the other. It is believed that eventually experiments will show that if a species can transmit one variety, it can also transmit the other. In all, there are ten species of Aedes mosquitoes which have transmitted the virus experimentally, but it is likely that they are not all of equal importance as vectors. Further investigation is needed to determine which species are actual vectors in nature and which are the most im- portant as carriers of the disease. Other Methods of Transmission. A discussion of the epidemiology of equine encephalomye- litis would not be complete without mention of other experi- mental and field data. Laboratory experiments repeated by various workers have demonstrated that equine encepha- Table I. Mosquitoes Known to Transmit Equine Encephalomyelitis to Laboratory Animals. Name of Mosquito. Western Variety. Eastern Variety. Occurrence in Massachusetts. Aedes aegypti X X 0 A. sollicitans X X X A. cantator X X X A. vexans ...... X X X A. triseriatus1 - X X A. atropalpus1 - X X A. taeniorhynchus .... X X X A. dorsalis X - X A. albopictus X - 0 A. nigromaculis X - 0 1 Work done at Harvard Medical School in 1939. lomyelitis is not transmitted by direct contact. Susceptible animals, which were caged with infected ones, failed to con- tract the disease in spite of the intimate contact when mos- 1941.] HOUSE —No. 2260. 17 quitoes were excluded. Field observations during epizootics revealed that multiple infections of horses in the same stable or on the same farm were rare. The evidence is therefore against infection by direct contact. In 1936 Syverton and Berry demonstrated that Derma- centor andersoni, the Rocky Mountain wood tick, was ca- pable of transmitting experimentally the western variety. The continuity of the virus through all stages in the develop- ment cycle of the tick, including survival through the egg stage, was definitely demonstrated. There is in ticks, there- fore, a potential vector and reservoir, especially during the winter months, "when cases of equine encephalomyelitis are rare and the ticks are hibernating. Besides ticks and mosquitoes, experiments on other poten- tial insect vectors have been made, especially on those that habitually bite horses and mules. Riley studied the insect transmission of disease due to filterable viruses, and con- cluded that the stable fly, Stomoxys calcitrans, the horsefly, Tabanus punctifer, and the horn fly, Haematobia serrata, were not capable of being vectors of equine encephalomyelitis. Possible Reservoirs of the Disease. In a disease with a broad host selectivity, such as equine encephalomyelitis, it is not unlikely that the reservoir of the disease may be found in one or more animals. Syverton and Berry suggested that small rodents, the gopher in par- ticular, which they found susceptible in experiments, may be the reservoir of the disease. Ten Broeck suggested that birds may be the reservoirs. Several investigators have carried out experiments on the susceptibility of birds and animals to equine encephalomyelitis. Recently, Davis has demonstrated that the eastern virus remains in the circulat- ing blood of birds for a period of three or four days. These birds rarely showed more than mild symptoms, and con- tinued their feeding as though they were perfectly well. These findings suggest that birds may be the natural host of the disease, and from them may have been transmitted 18 HOUSE— No. 2260. [Jan. in Massachusetts in 1938 to horses, which have no natural immunity to the disease. The recognition of the occur- rence of the disease in man is most recent. Thus far all infections of man have occurred during outbreaks of the disease in horses, indicating that man may be in danger only when the virus is unusually prevalent, as evidenced by the outbreak among horses. The Massachusetts Outbreak of Equine Encephalomyelitis. Epidemiology. In July, 1938, for the first time recorded in the State, equine encephalomyelitis occurred among horses in Massa- chusetts. In the course of about ten weeks, 269 deaths were reported. The geographical distribution of deaths in horses and cases in humans is given in Map I. The disease made its first appearance in the basin of the Taunton River, which drains into near-by Rhode Island. The outbreak spread mainly in a northeasterly direction into the upper parts of the Taunton River drainage area. There were rela- tively few cases to the south and southeast and none on Cape Cod, which is separated from this area by Buzzards Bay and the Cape Cod Canal. The outbreak also spread northward to metropolitan Boston, and isolated cases oc- curred in a thirty mile square, extending from the mouth of the Taunton River in the south to Boston on the north, and from the boundary of Rhode Island, northeastward to the coast of Massachusetts. Rhode Island to the west reported 55 cases and Connecticut 29. 1941.] HOUSE— No. 2260. 19 MAP I DISTRIBUTION OF EQUINE ENCEPHALOMYELITIS MASSACHUSETTS 1938 LEGEND CASES IN HUMANS DEATHS IN HORSES 20 HOUSE —No. 2260. [Jan. During the summer and early autumn of 1938 rainfall in southeastern Massachusetts and Rhode Island was unusu- ally heavy, and as a result mosquitoes were unusually prev- alent in these areas. The prevailing winds in that region are from the southwest; and since the outbreak spread mainly in a northeasterly direction, it would seem that infectious mosquitoes may have been carried by these winds and may have widened the spread of the disease. Horses which were apparently well were moved from one country fair to another; in one such instance a horse was moved thirty miles from an area where the disease was prevalent to the northeast to a town near the coast. Al- though without symptoms when moved, the horse became ill on the following day and a diagnosis of equine encepha- lomyelitis was proved by the isolation of the virus from its brain. Thus the movement of infectious horses may have been a factor in the spread of the disease. During the outbreak, Fothergill and Dingle isolated the eastern virus from the brains of a pigeon that died in southeastern Mas- sachusetts, and Tyzzer, Sellards and Bennett isolated the same virus from the brains of ring-necked pheasants from Connecticut. These findings suggested that birds may be the reservoirs of the disease and may be factors in its spread. Almost simultaneously, in the same area, a new type of encephalitis appeared in man, particularly among children. Investigations by the Department of Public Health in co- operation with the Rockefeller Institute and Harvard Medi- cal School revealed that human infections were due to the same virus causing disease in horses. The prevalence of the disease among horses and humans is given in Graph I. The median date of reported deaths among horses occurred during the week ending August 27, or two weeks in advance of the median date of onset for cases in humans. Appar- ently, the peak of the outbreak among horses preceded that of the outbreak among humans by an interval of over two weeks. Although the prevalence of the disease was much greater among horses than among humans, the rise and fall of the outbreak in these groups was the same. The outbreak among horses began slowly without increase 1941.] HOUSE —No. 2260. 21 seasonal incidence or EQUINE encephalomyelitis MASSACHUSETTS 1938 LEGEND HUMAN CASES DEATHS IN HORSES Graph I. HOUSE —No. 2260. 22 [Jan. for four weeks; and then rapidly reached its peak in two weeks. Remaining at this peak level for about a week, the outbreak subsided more slowly than it began. The last case was reported late in October, sixteen weeks after the beginning of the outbreak. There were no multiple cases among families, and mul- tiple cases on the same farm or in the same stable were rare among horses. These field observations confirmed ex- perimental evidence that the disease is not transmitted by contact. There were thirty-four human cases during the outbreak. Of this number, 25, or 73 per cent, proved fatal. This in- dicates the seriousness of the disease is that few of those affected recover, although it is not likely that the number of cases will ever assume large proportions. Other Mosquito-Borne Diseases. Although equine encephalomyelitis and malaria are the two most important mosquito-borne diseases which have occurred in Massachusetts, there are certain other diseases, some of which are, and some of which are suspected of be- ing, mosquito-borne and which either occur or may occur in this State. These diseases have been placed in three groups in Table 11. All of them have occurred in the United States, and are therefore considered as possible invaders of Massachusetts. Equine encephalomyelitis is included for the sake of completeness. Table 11. Diseases with Proved and Suspected Mosquito Transmission in the United States. Proved Mosquito Transmission. Laboratory Mosquito Transmission. Suspected Mosquito Transmission. Malaria.1 Yellow fever.2 Dengue.3 Filariasis.3 Equine encephalomyelitis.1 Lymphocytic choriomeningitis.1 Poliomyelitis.1 St. Louis encephalitis.3 1 Currently present in Massachusetts. 2 Formerly present in Massachusetts. 8 Not known to be indigenous in Massachusetts. 1941.] HOUSE— No. 2260. 23 Diseases with Proved Mosquito Transmission. Malaria is the most widely distributed mosquito-borne disease in the world. It has caused more suffering and death than any other single insect-borne disease. There have been cases of malaria in Massachusetts from early colonial times, and it is apparent that there have been at least three epidemic waves of malaria in the State. Since 1890 malaria has continued to decrease, and during the past ten years only eleven reported cases were acquired inside of Massachusetts. In colonial times yellow fever appeared in New England. It was brought to port cities by sailing vessels which came from areas in the tropics and subtropics, where yellow fever was endemic. The mosquito, Aedes aegypti, carrier of the disease, was able to survive on board these ships, breeding in water casks. Under favorable meteorological conditions and a temperature of over 72° F., Aedes aegypti were able to survive, breed and transmit the virus in northern climates until the arrival of colder weather. Yellow fever may reappear in Massachusetts only if infected Aedes aegypti are imported; if these mosquitoes breed in large enough numbers to be temporarily established; and if the infected mosquitoes bite people, who, in turn, become ill, and infect Aedes aegypti. However, the importation of yellow fever is highly improbable, not only because of the lack of breeding places on modern steamships, but chiefly because of the efforts of the United States Public Health Service, which quarantines all vessels and airplanes which come from areas where the disease is endemic, or takes such measures as to ensure the destruction of Aedes aegypti on board ships or planes. Dengue has never been known to exist in Massachusetts, although it has spread in epidemic waves through several of the Southern States. Filariasis is, in the main, restricted to tropical and subtropical regions. However, indigenous cases have occurred in South Carolina. This disease has not shown any evidence of extending to neighboring areas, and the chance of this disease reaching Massachusetts is very small. 24 HOUSE— No. 2260. [Jan. Diseases with Suspected Mosquito Transmission. Observations in Massachusetts indicate that there is no correlation between the prevalence of mosquitoes and the existence of poliomyelitis. Evidence supports the theory that poliomyelitis is not transmitted by mosquitoes. To date, St. Louis encephalitis has not been reported in Massa- chusetts. However, its recognition in such widely separated areas as Indiana and California indicates that the disease has involved hitherto unsuspected areas. The problem of mosquito transmission of St. Louis encephalitis remains unsolved. Further investigation must determine the role of the mosquito in this disease. Its seasonal distribution and the epidemiological observation indicate that St. Louis encephalitis may be mosquito-borne. The control of any mosquito-borne disease is based on one or more of the following procedures: The Control of Mosquito-Borne Diseases. I. Control of the mosquito vector. 11. Protection of man and animal from the bite of infected mosquitoes. 111. Immunization of susceptibles. IV. Removal of sources of infection of mosquito vectors by (a) Isolation of cases. (ib) Treatment of carriers. V. Prevention of entry of the mosquito vector and possible sources of infection into areas as unaffected by the disease. All these methods are not applicable to every mosquito- borne disease. The decision as to which methods are to be employed must be based on an ultimate knowledge of the disease in question and the habits and prevalence of the mosquito-carrier of the disease. Certain conditions are necessary before a mosquito-borne disease can become prevalent in any area. One of these conditions is the existence of a certain numerical relation- ship between the hosts, vectors and susceptibles. When this numerical relationship becomes upset by a reduction of the number of vectors, the disease ceases to be epidemic and rapidly declines. 1941.] HOUSE— No. 2260. 25 The life history and habits of mosquitoes are such that control measures may be designed to eliminate or control either the larvae or the adults. The measures which are most effective in any area depend upon the local factors and upon the genus and species of any mosquitoes concerned. It is impractical and uneconomical to attempt to control all mosquitoes. The control measures must be directed against that species which it is desired to reduce below the critical level. Mosquito control has been effective in malaria and yel- low fever. There has been considerably less experience in the effectiveness of this method in dengue, but since the principal vector of this disease is the same as for yellow fever, there is every reason to believe that mosquito con- trol will prove just as effective. Protection from the bites of mosquitoes can be accomplished only under very limited conditions. Screening and avoidance of unnecessary ex- posure are the methods most effective. Spraying in houses, the application of mosquito repellants and swatting of adults are adjuvants. Specific immunization appears to be of value in yellow fever. In equine encephalomyelitis a vaccine produced from formolized virus grown in chick embryos has proved effective in the protection of horses. As yet, this vaccine is not applicable to man, except for laboratory workers, due to severe reactions which have been encountered. Moreover, the risk of exposure to the disease has been so small that community immunization has not been indicated. Vaccination of horses must be repeated annually, as immunity is temporary. Mohler at- tributes the decreased incidence of this disease in 1939, in part, to the vaccination of horses. Malaria and filariasis are often spread by infected per- sons who are not known to have the disease. In modern civilization and rapid transportation it is practically im- possible to eliminate the travel of such individuals. In summary it may be said that when control methods are dependent upon control of man, only limited success may be expected, as some individuals are unco-operative. The most effective method in the control of mosquito-borne dis- 26 HOUSE No. 2260. [Jan. eases has been the reduction of vectors to below the critical level. The choice as to what method is to be used in the control of a disease depends upon the peculiarities of that disease, and upon the available means for carrying out the necessary procedures. Personnel and Methods. In addition to the co-operation of the Work Projects Administration, various Federal, state and private organ- izations participated in the activities of the survey. Ex- clusive of the technical director and the entomologists, the regular personnel of the survey were all Work Projects Administration employees. As it was desired to make regular periodic collections at prescribed points throughout the Commonwealth, such places as were thought likely to be permanent collection points were marked on topographical maps. A collection point was defined as an area 100 yards in radius about some permanent landmark as a center. Such a collection point may have been in the woods, meadow or at the edge of a large pond. In the last instance the center chosen was a prominent, easily identified landmark on the shore, and the collection point area extended 100 yards in either direc- tion along the shore and 100 yards inland. During the first two weeks of the survey, while the field personnel was being trained, collections were small in num- ber. Collections were started on a state-wide basis during the first week of July. Toward the end of July the crews were familiar with their districts, and collection points were established in most of the towns. By the end of July, with few exceptions, collections were being made from most of the towns in the Commonwealth. Thereafter the number of collections continued to increase and reached a maxi- mum late in September. The months of May, June and July, 1939, were exceptionally dry. The normal rainfall for these months is 10.25 inches. In 1939 only 6.53 inches of rain fell during the period, or about two thirds of the normal. Many marshes, small ponds and streams dried up, others decreased in size, and puddles and small collec- tions of water were practically non-existent. 1941.] HOUSE —No. 2260. 27 This lack of rainfall was reflected in the diminution in the number of mosquitoes. In 1938 mosquitoes were unu- sually prevalent, due to the heavy rainfall throughout the summer and early autumn and the flood in many river val- leys in July; in 1939 mosquitoes were comparatively scarce. Although there are no established data on the prevalence of mosquitoes in 1938, the observations of mosquito control personnel may be taken as a measure. These workers, as well as residents, observed that during 1938 mosquitoes were unusually prevalent throughout Massachusetts. In 1939, on the other hand, mosquitoes were so scarce that vacationists reported they were able to sleep in the open without screens or netting. Because of these meteorological conditions in 1939, col- lections of mosquitoes were quite difficult during July. Due to the fact that many ponds, marshes and streams practi- cally dried up, new collection points had to be established. In August increased rainfall was reflected in the increased prevalence of mosquitoes. The number of collections in August increased, and in September reached a maximum. However, there was not enough rain to compensate for the three preceding dry months, and water collections be- gan to decrease again in size and number. At no time dur- ing the summer and autumn of 1939 was there a normal prevalence of mosquitoes. At the beginning of the survey identifications were based upon Tulloch’s key, which was published in 1930. When about one hundred thousand specimens had been identified, enough data were collected to revise this key, and, as one of the objectives of the survey, a new key was used through- out the remainder of the project. It is adaptable to use in New England and perhaps in New York as well. In a survey of this type only a relatively small sample of the entire mosquito population can be studied. Therefore, in order to be in a position to generalize about the whole, the sample has to be representative of the population. In this survey the selection of samples has been carefully avoided. For the purpose of this analysis, a mosquito collection is defined as the finding of either one or more adults or one 28 HOUSE No. 2260. [Jan. or more larvae of one species of mosquitoes in one location. If, in a single sample, there are more than one species of larvae, this sample is counted as a separate collection for each of the species represented. By definition, it is im- possible to have both adults and larvae in the same collec- tion, as the former are collected from a different location than the latter. Of the total (47,232) collections of biting mosquitoes, 83.1 per cent, or 39,254 collections were lar- vae. The proportion of adults to larvae varied in the vari- ous counties. In Barnstable County adult collections were the largest, both in number and in per cent, representing 32,5 per cent of the total in that county. In Hampshire County, adult collections comprised only 5.3 per cent of the total. Table 111. —Summary of Mosquito Collections, 1939. County. Adults. Larvae. Total. Barnstable 1,371 2,843 4,214 Berkshire ....... 466 4,312 4,778 Bristol 202 1,842 2,044 Dukes and Nantucket 614 1,546 2,160 Essex 1,024 3,644 4,668 Franklin 405 2,369 2,774 Hampden 209 2,976 3,185 Hampshire 84 1,488 1,572 Middlesex 1,195 6,109 7,304 Norfolk 457 2,441 2,898 Plymouth 803 3,818 4,621 Suffolk 155 382 537 Worcester 993 5,484 6,477 Total 7,978 39,254 47,232 The number of collections as determined by punch card analysis is summarized in Table IV. The totals for adults and larvae and the per cent distribution of each are given by weeks. There was a peak in the number of adults dur- ing the weeks of June 11 to the 24th, inclusive, and a grad- ual decline thereafter throughout the duration of the sur- vey. The explanation for this distribution of the adult collections rests on the fact that, subsequent to the week 1941.] HOUSE— No. 2260. 29 of July 9 to 15, there was a disproportionate increase in the number of larvae, due to improved breeding condi- tions, and hence adults formed a relatively smaller pro- portion as more larvae were collected. Collections per Square Mile. The plan of the survey was made on the basis of the city or town constituting the area unit. The number of collec- tions per square mile varied from community to commu- nity. Collections were made in all the cities and towns except two. The number of collections per square mile averaged 9 (8.93). Those communities in which the head- quarters of the crews were located invariably had larger collections —in some cases 30 or more per square mile. The response of volunteer collectors varied greatly in differ- ent communities, and was responsible for unusually high coverage in the communities of Brookline and those in Barnstable County, where a large proportion of the collec- tions was made by mosquito control workers. Lastly, it must be borne in mind that the towns vary greatly in area. This is a factor which cannot be practically evaluated. When a community was large, attempts were made to in- crease proportionately the amount of time devoted to col- lecting each week. Table IV. Mos 17.0 83.0 1 Collections prior to June 24 were made by departmental personnel and volunteers. 2 Collections after October 28 were largely on Martha’s Vineyard, where the season is late. A few scattered collections were made by volunteers. 3 These figures were obtained from the punch card analysis by interpolation from serial group- ing. The actual total was 47,232. 1941.] HOUSE —No. 2260. 31 Influence of Meteorological Conditions on Mosquitoes. Rain. It was confirmed by field observations that there is an increase in mosquito breeding after heavy rains. However, the ponds and streams were so low in the summer of 1939 that many remained below normal levels throughout the season. The association of rain and mosquitoes becomes more apparent on comparison of the 1938 and 1939 precipi- tation data. During 1938 there was an accumulation of 11.7 inches of rain above normal, an excess of 26 per cent. That year mosquitoes were unusually prevalent throughout the State. In 1939 there was a deficit of 5.5 inches of rain, 13 per cent below normal. Mosquitoes were at no time as prevalent as in other years. The 1938 rainfall was far above normal in June, July and September; in 1939 rain- fall was below normal during the mosquito season. (See Graph II.) HOUSE No. 2260. [Jan, PRECIPITATION MASSACHUSETTS 1938 & 1939 Graph 11. 1941.] HOUSE —No. 2260. 33 Temperature. During 1939 the temperature showed little deviation from normal. A deficit in Fahrenheit degree-days devel- oped in April and remained unchanged through July. In August an excess accumulated which lasted through Octo- ber. Warm weather is conducive to increased mosquito breeding. However, the slight excess which accumulated at the end of the summer had little effect because of the lack of standing water. Again we contrast 1939 with 1938, and find that 1938 was a more favorable year for mosqui- toes. The summer of 1938 was not only wetter but warmer, and mosquito breedimg conditicns were nearer the opti- mum. Wind. Adult mosquitoes, when borne by winds, will be dissemi- nated over a large area in the direction taken by the wind. The direction of prevailing winds for the towns in which collections were made by the Standard United States Weather Bureau Method. Table V lists the direction of the prevailing winds in the towns in which collections were made: Table V. Direction of Prevailing Winds. Week ending — Direction. Week ending — Direction. July 1 SW Sept. 2 W July 8 SW Sept. 9 SW July 15 SW Sept. 16 SW July 22 SW Sept. 23 SW July 29 SW Sept. 30 SW Aug. 5 ..... w Oct. 7 NW Aug. 12 ..... w Oct. 14 NW Aug. 19 w Oct. 21 NW Aug. 26 w Oct. 28 NW As the prevailing winds throughout the middle and early parts of the summer are from the west and southwest, the carrying of mosquitoes by the wind is chiefly to the east and northeast. Salt marsh mosquitoes were therefore carried in a northeasterly direction. In those areas of the State 34 HOUSE No. 2260. [Jan. which are northeast of salt water, adults of salt marsh mosquitoes may be expected to be found farther inland than where salt water is to the northeast. The dissemina- tion of a mosquito-borne disease would be more extensive in the direction taken by the prevailing winds. Table VI was compiled by punch card analysis from the data recorded in these surveys. Samples were not taken from identical sources in an area less than 100 yards in radius. There were twenty different types of breeding Mosquito Breeding Places. Table VI. Mosquito Breeding Places at Regular Collection Points. Type of Breeding Places. Number of Breed- ing Places. Number of Species Collected. Number of Collections.1 Average Number of Collections Per Breed- ing Place. 1. Artificial pool .... 46 7 435 9.5 2. Barrel 82 10 789 9.6 3. Bird bath, flower pot . 6 4 63 10.5 4. Cesspool or overflow . 14 7 128 9.1 5. Cistern 9 5 62 6.9 6. Dump 92 13 1,064 11.6 7. Watering trough .... 27 9 273 10.1 8. Cranberry bog . . . 88 18 1,352 15.4 9. Excavation 19 11 185 9.7 10. Quarry 2 5 27 13.5 11. Sand pit 7 6 47 6.7 12. Root hole 22 9 175 7.9 13. Tree hole 15 8 187 12.5 14. Well 13 11 169 13.0 15. Marsh or swamp .... 637 15 7,781 12.2 16. Pond or lake .... 468 15 5,025 10.7 17. Puddle 110 14 1,012 9.2 18. River or stream .... 1,173 17 10,519 9.0 19. Rocky crevice .... 9 8 69 7.6 20. Running and still water combined 382 18 3,805 9.9 Total 3,221 - 33,167 10.3 1 Does not include specimens collected by volunteers 1941.] HOUSE —No. 2260. 35 places included in our analysis. Streams, marshes, swamps, ponds and lakes were most frequent. Dumps and barrels were the two most common man-made breeding places. Lastly, not all species were found in the same collection point. Certain species were found in the same water collec- tion with a greater frequency than others. The association of certain vectors of equine encephalomyelitis with other species are summarized in Table VII. Aedes atropalpus was found to be most frequently associated with Culex pipiens. All other vectors were associated with Culex apicalis and Culex pipiens to about the same degree. It is to be noted that these associations are between species collected in a collection point 100 yards in diameter throughout the entire season. The species may not have been collected at the same time nor from the same water collection. However, in the majority of the cases there was only one water body at a collection point, and therefore the associations hold as to place better than as to time. There is very little positive association between the various salt marsh mosquitoes. This observation may be explained in part by the fact that Aedes cantator may breed in water containing less salt than that in which Aedes sollici- tans breed. The fresh water Aedes vectors are significantly associated with Culex territans which was collected in much smaller numbers than other species of Culex. In all these tables only a few attempts have been made to interpret the data. Too many factors are concerned in the ecology and bionomics of mosquitoes to assign any one observation to a peculiar circumstance without due con- sideration of all other factors. 36 HOUSE No. 2260. [Jan Table VII. Association of Larvae at Collection Points.1 Number of Collections. Species. Aedes. Atropalpus. Cantator. Sollicitans. Triseriatus. Vexans. Aedes atropalpus - - - - 41 A. canadensis . - 12 1 - 6 A. cantator - - 50 1 80 A. cinereus - 15 4 - 31 A. excruoians . - - - - 3 A. fitchii .... - - - - - A. intrudens 1 - - - 3 A. sollicitans . - 83 - - - A. stimulans - - - - - A. taeniorhynchus . - 15 16 - - A. triseriatus . - 1 - - 2 A. vexans 13 45 11 2 - Anopheles punotipennis . 30 13 8 10 382 A. quadrimaculatus 2 9 14 - 82 Culex apicalis . 34 449 123 43 1,088 C. pipiens 89 368 135 43 844 C. salinarius 3 215 91 - 109 C. territans 47 63 15 42 438 Theobaldia melanura - 47 8 1 42 T. morsitans - - - - 1 Total . 219 1,335 476 142 3,152 i Number of collections of larvae of other species at were found some time during the season. collection points where certain vectors 1941.] HOUSE No. 2260. 37 Table VII. Association of Larvae at Collection Points1 Concluded. Per Cent of Collections. Species. Aedes. Atropalpus. Cantator. Sollicitans. Triseriatus. Vexans. Aedes atropalpus - - - - 1.3 A. canadensis . - .9 .1 - 2 A. cantator - - 10.5 .7 2.5 A. cinereus - 1.1 .8 - 1.0 A. excrucians . - - - - .1 A. fitchii .... - - - - - A. intrudens .5 - - - .1 A. sollicitans - 6.2 - - - A. stimulans - - - - - A. taeniorhynchus . - 1.1 3.4 - - A. triseriatus . - .1 - - .1 A. vexans .... 5.9 3.4 2.3 1.4 - Anopheles punctipennis . 13.7 1.0 1.7 7.0 12.1 A. quadrimaculatus .9 .7 2.9 - 2.6 Culex apicalis . 15.5 33.6 25.8 30.3 34.5 C. pipiens 40.6 27.6 28.4 30.3 26.8 C. salinarius 1.4 16.1 19.1 - 3.5 C. territans 21.5 4.7 3.2 29.6 13.9 Theobaldia melanura - 3.5 1.7 .7 1.3 T. morsitans - - - - - Total .... 100.0 100.0 100.0 100.0 100.0 1 Number of collections of larvae of other species at collection points where certain vectors were found some time during the season. 38 HOUSE No. 2260. [Jan. The Collection of Adult Mosquitoes. Adult mosquitoes were collected by two methods. The most important of these was the capture of specimens by the killing tube, which was placed directly over the resting mosquito. The second method was sweeping with nets. As the collectors were novices in using the net, and since some experience is required in its manipulation, this method was less productive than the former. There were 23,484 specimens in 7,978 collections. Adults represented 16.9 per cent of the total collections. Although 75 per cent or more of the adults were collected by the personnel of the survey, and hence represented collections of those adults with diurnal habits, the remainder of the collections were made by volunteers and contain a higher proportion of mosquitoes with nocturnal habits. Biting Habits. These data are summarized in the following series of tables. In Table VIII are listed those mosquitoes which were collected by placing the killing tube over a mosquito which was resting on a person’s body. Although the mos- quito may not have been biting, it presumably was attracted to man in the anticipation of obtaining blood. Aedes sollicitans is the most numerous offender. Mansonia per- turbans is a ferocious biter, but ceases to be a nuisance about the time that the disease may be expected to increase in prevalence. Aedes sollicitans was more numerous towards the middle and end of the mosquito season. Aedes cantator and Aedes vexans were more prevalent during the middle of the season. These last three are vectors of equine encephalomyelitis and were the three most numerous biters. There was much variation in the relative percentages of the mosquitoes which were collected inside houses and those which were collected on man. Those which were collected inside houses were contributed by volunteers who were interested in finding out what mosquitoes interrupted their slumbers. Those in Table IX, therefore, represent mos- quitoes with greater nocturnal biting habits as contrasted 1941.] HOUSE No. 2260. 39 Table VIII. Adult Mosquitoes Caught on Man. Species. Number of Specimens. Per Cent. Aedes sollicitans 738 37.3 Mansonia periurban s 511 25.8 Aedes cantator 311 15.7 Aedes vexans ...» 120 6.0 Aedes aurifer 52 2.6 Aedes canadensis 50 2.5 Aedes cinereus 47 2.4 Culex pipiens 42 2.1 Aedes excrucians 20 1.1 Aedes intrudens 19 0.9 Culex salinarius 14 0.7 Aedes taeniorhynchus 12 0.6 Culex territans . 10 0.5 Anopheles punctipennis 7 0.4 Culex apicalis 6 0.3 Aedes fitchii 4 0.2 Aedes triseriatus 3 0.2 Theobaldia melanura 3 0.2 Aedes species unidentified 3 0.2 Aedes stimulans 2 0.1 Anopheles quadrimaculatus 2 0.1 Aedes dorsalis 1 0.0 Total 99.9 with those in Table VIII, where diurnal activity predomi- nated. Culex pipiens and Mansonia perturbans are the most frequent invaders. Anopheles quadrimaoulatus, the malaria vector, is third. Culex apicalis, which is described as a biter of cold-blooded animals, was fourth in this series. The Aedes mosquitoes were infrequent invaders of homes, and were not a serious menace inside buildings. This observa- tion indicates that the greatest danger from vectors of equine encephalomyelitis is outdoors. In evaluating the data above, it is necessary to point out that all mosquitoes do not enter houses with the intent to bite. Although most mosquitoes are attracted indoors with 40 HOUSE No. 2260. [Jan. the prospect of a blood meal, some species, such as Culex apicalis, enter buildings principally to hibernate. With the approach of cold weather mosquitoes are more likely to seek warm winter quarters. When the mosquitoes caught in houses are added to those which are caught on man, a better index of the biting mosquitoes can be obtained. These data are compiled in Table X. Table IX. Adult Mosquitoes Caught in Houses. Species. Number of Specimens. Per Cent. Culex pipiens 973 31.1 Mansonia perturbans 911 29.1 Anopheles quadrimaculatus 407 13.0 Culex apicalis 189 6.0 Culex territans 165 5.3 Culex salinarius 85 2.7 Aedes cantator 56 1.8 Aedes sollicitans . 56 1.8 Anopheles punctipennis 46 1.5 Aedes vexans 44 1.4 Anopheles maculipennis ........ 27 .9 Culex species unidentified 26 .8 Anopheles walkeri 23 .7 Aedes triseriatus 19 .6 Aedes canadensis 17 .5 Theobaldia melanura ........ 14 .4 Aedes atropalpus 12 .4 Aedes excrucians 12 .4 Aedes aurifer 11 .3- Aedes cinereus 10 .3 Aedes trivittatus 9 .3 Aedes fitchii 6 .2 Aedes intrudens 3 .1 Aedes species unidentified 3 .L Chaoborinae species unidentified 3 .1 Aedes stimulans 1 0.0 Aedes punctor 1 0.0 Theobaldia morsitans 1 0.0 Total 3,130 99.8 1941.] HOUSE —No. 2260. 41 Table X. Adult Mosquitoes Caught on Man and in Houses. Species. Number of Specimens. Per Cent. Mansonia perturbans 1,422 27.8 Culex pipiens 1,015 19.8 Aedes sollicitans 794 15.5 Anopheles quadrimaculatus 409 8.0 Aedes cantator . 367 7.1 Culex apicalis . 195 3.8 Culex territans . 175 3.4 Aedes vexans 164 3.2 Culex salinarius 99 1.9 Aedes canadensis 67 1.3 Aedes aurifer 63 1.2 Aedes cinereus . 57 1.1 Anopheles punctipennis . 53 1.0 Aedes excrucians 32 ,6 Anopheles maeulipennis . 27 .5 Culex species unidentified 26 .5 Anopheles walkeri 23 .5 Aedes triseriatus 22 .4 Aedes intrudens 22 .4 Theobaldia melanura 17 .3 Aedes atropalpus 12 .2 Aedes taeniorhynchus 12 .2 Aedes fitchii 10 .2 Aedes trivittatus 9 ,2 Aedes species unidentified 6 .1 Chaoborinae species unidentified 3 .1 Aedes stimulans 3 .1 Aedes dorsalis 1 0.0 Aedes punotor . 1 0.0 Theobaldia moraitans 1 0.0 5,107 99.4 Here the species are rearranged as to their numerical importance: Mansonia perturbans heads the list, Culex pipiens is second, Aedes sollicitans is third, and Anopheles quadrimaculatus, fourth. Among the species captured in 42 HOUSE No. 2260. [Jan. houses, the vectors of equine encephalomyelitis represent about one fourth of the total number of specimens. Table XI lists the mosquitoes caught in barns and stables. Presumably, the main attraction was the prospect of a blood meal. Here, however, the blood was not from man, but from horses, cattle and other domestic animals. A second urge which became effective with the onset of cold weather was the seeking of a warm place in which to hibernate. Culex pipiens was by far the most frequent invader of the barn and stable. Mansonia perturhans was the second in numerical importance, and Aedes vexans, third. Aedes sollicitans, which is a ferocious biter of man, was caught only once inside a barn or stable. Table XL Adult Mosquitoes Caught in Barn and Stable. Species. Number of Specimens. Per Cent. Culex pipiens 98 46.4 Mansonia perturbans 35 16.6 Aedes vexans 18 8.5 Aedes cantator 14 6.6 Culex salinarius 13 6.2 Culex apicalis 8 3.8 Anopheles quadrimaculatus 4 1.9 Culex territans 4 1.9 Culex species unidentified 4 1.9 Aedes cinereus 3 1.4 Aedes excrucians 3 1.4 Anopheles punctipennis 3 1.4 Aedes atropalpus 1 .5 Aedes fitchii 1 .5 Aedes sollicitans 1 .5 Aedes stimulans 1 .5 Total 211 100.0 Environment. The collection of those species of adult mosquitoes which are of public health importance in different types of terrain is summarized in Table XII. These data are based on 1941.] HOUSE No. 2260. 43 adults caught at regular collection points. It is to be ex- pected that collections were made more often in certain types of terrain in preference to others. Cultivated fields were seldom trespassed upon, and hence only a few collec- tions were made here. The description of the collection point area as given in this table is the chief character of the land included in the 100-yard radius of the collection point. In many instances other types of terrain were also present, but represented only a small portion of the collec- tion point area. The totals on the left of Table XII fur- nish a base against which the species data can be compared. Aedes cantator and Aedes sollicitans were caught with about equal frequency in meadows and in woods. Aedes vexans was captured most frequently in the woods. The prefer- ence of this mosquito for the woods is an important factor in any control-program that may be instituted against equine encephalomyelitis. Horses should be removed from pastures that are in close proximity to woods, and people should refrain from entering woods during outbreaks of this disease. In this way exposure to Aedes vexans, which may be infectious, will be greatly reduced. In applying the data collected by this survey, it seems apparent that perhaps one half of the exposures to Aedes vexans would be eliminated simply by keeping away from the woods. These facts seem to apply to Aedes triseriatus and to Anopheles quadrimaculatus, the principal vector of malaria; however, the number of collections in both these instances is smaller and statistically this conclusion is less certain. Aedes atropalpus and Aedes taeniorhynchus were captured in too small a number to permit any significant inference. 44 HOUSE No. 2260. [Jan. Nattjbb of Terrain. Aedes. Anopheles. Totals. Atropalpus. Cantator. Sollicitana. Taeniorhy nchus. Triseriatus, Vexans. Quadrimaculatus. Cultivated fields - 7 10 - - 7 3 27 Meadow — pastured - 11 32 1 4 1 2 51 Meadow — unpastured .... - 102 177 8 2 16 10 315 Rocky - - - - - 1 3 4 Woods - 67 92 3 16 56 14 248 Meadow and woods - 70 99 1 5 24 5 204 Meadows and cultivated fields . 1 11 20 - 2 4 2 40 Total 1 268 430 13 29 109 39 889 Per Cent of Collections. Cultivated fields - 2.6 2.6 - - 6.4 7.7 3.0 Meadow — pastured - 4.1 7.4 7.7 13.8 0.9 5.1 5.7 Meadow — unpastured .... - 38.1 41.1 61.5 6.8 14.6 25.6 35.5 Rocky - - - - - .9 7.7 .4 Woods - 25.0 21.3 23.1 55.6 51.3 35.9 27.9 Meadow and woods - 26.1 23 1 7.7 17.2 22.0 12.8 23.0 Meadows and cultivated fields 100 4.1 4.6 - 6.8 3.7 5.1 4.S Total 100 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Table XII. Association of Vector Adults ivith Different Types of Terrain. Number of Collections. 1941.] HOUSE —No. 2260. Vectors of Equine Encephalomyelitis. Numerical Importance of Vectors. There are six mosquitoes in Massachusetts which have been demonstrated in the laboratory to transmit the east- ern vims. These are all Aedes mosquitoes. Their numeri- cal importance in relation to other species, both vectors and non-vectors, is discussed in this section. The geo- graphical and seasonal distribution, the life habits, and public health importance of such species are discussed in a later section. Table XIII. Numerical Importance of Vectors of Equine Encephalo- myelitis, by Specimens. Species. Adults . Labvae. Speci- mens. Numerical Importance in Per Cent. Number. Per Cent. Number, Per Cent. Aedes atropalpus 60 5.7 993 94.3 1,053 7.8 A. cantator 1,329 33.0 2,701 67.0 4,030 29.7 A. sollicitans 2,548 70.7 1,054 29.3 3,602 26.6 A. taeniorhynchus . 20 15.2 112 84.8 132 1.0 A. triseriatus . 228 71.3 92 29.7 320 2.4 A. vexans . 1,052 24.0 3,358 76.0 4,410 32.5 Total . 5,237 38.7 8,310 61.3 13,547 100.0 In Table XIII the vectors are evaluated on the basis of the number of specimens collected, A. vexans was the most numerous, A. cantator and A. sollicitans were second and third, respectively, in numerical importance. The other three vectors were far below these in numbers. The per cent of adult specimens was highest in A. sollicitans and in A. triseriatus; the latter, however, was caught in much smaller numbers. The number of vectors collected varied from one section of the State to another. Collections of larvae and adults combined are tabulated by counties in Table XIV. A. atropalpus larvae were collected in five counties, three in the Connecticut River Valley, one in the northeastern part 46 HOUSE No. 2260. [Jan. of the State, and one on Cape Cod. A. cantator and A. sollicitans were collected only in the counties along the coast, and A. taeniorhynchus only in Dukes County. A. tri- seriatus was collected in small numbers in most of the counties. A. vexans was the most numerous species and was collected in all counties. Of the specimens collected in Dukes and Nantucket counties, 23.2 per cent were vec- tors, and of those collected in Barnstable County 13.7 per cent were vectors. Equine encephalomyelitis, however, has not been reported from these areas. In the remainder of the counties there was no significant difference in the per cent of larvae of vector species. Considering adult specimens only, the per cent which were vectors varied more markedly from county to county. Table XV summarizes these data. A. atropalpus adults were collected in small numbers in the Connecticut River Valley and in northeastern Massachusetts and on Cape Cod. A. cantator and A. sollicitans adults were collected in the coastal regions, and, occasionally, further inland. A. triseriatus and A. vexans adults were captured in all counties, the latter being found in far greater numbers. In Dukes and Nantucket counties 76.3 per cent of the adult specimens were vectors. This figure is much higher than elsewhere in the State. In Essex and Barnstable counties the vectors represented 30.8 per cent and 27.9 per cent, respectively. Bristol County vectors made up 15.3 per cent of the adult specimens. Vectors comprised 9.6 per cent to 21.8 per cent in Franklin, Hampden, Hamp- shire, Norfolk and Suffolk counties. In Berkshire, Middle- sex and Worcester counties vectors comprised 3.9 per cent, 6.0 per cent and 6.5 per cent, respectively, a statistical significant difference. 1941.] HOUSE —No. 2269 47 County. Abdes. Total Vectors. Total Aedes. Per Cent Vectors. Total All Genera. Per Cent Vectors. Atropalpus. Cantator. Sollicitans. Taeniorhyn- chus. Triseriatus. Vexans. Barnstable .... 12 1,780 1,198 0 7 1,751 4,748 6,561 72.4 34,653 13.7 Berkshire .... 0 0 0 0 45 341 386 447 86.2 25,948 1.6 Bristol 0 281 10 0 12 223 526 615 85.5 14,095 3,7 Dukes1 0 975 1,337 131 3 246 2,692 2,811 95.7 11,623 23.2 Essex 12 414 658 0 15 87 1,186 1,452 81.7 30,535 3.9 Franklin 183 0 0 0 46 192 421 471 89.3 12,724 3.3 Hampden .... 810 0 0 0 34 395 1,239 1,338 92.6 17,964 6.9 Hampshire .... 34 0 0 0 13 226 273 303 90 0 8,948 3.1 Middlesex .... 1 100 98 0 10 188 397 577 68.8 45,915 .9 Norfolk ..... 0 159 140 0 58 66 423 902 46.9 16,210 2.6 Plymouth .... 0 291 126 1 9 411 838 1,316 63.7 18,663 4.5 Suffolk 0 30 35 0 10 11 86 118 72.9 5,459 1.6 Worcester .... 1 0 0 0 58 273 332 717 46.3 30,350 1.1 Total .... 1,053 4,030 3,602 132 320 4,410 13,547 17,628 76.8 273,087 5.0 • 1 Including Nantucket. Table XIV. Numerical Importance of Vectors, by counties. Combined Total of Adults and Larvae, Massachusetts, 1939. 48 HOUSE No. 2260. [Jan. Adult Specimens, Aedes. Per Cent of Collections which were Vectors. Atropalpus. Cantator. Sollicitans. Taeniorhyn- chus. Triseriatus. Vexans. Vectors. All Species. Barnstable 12 439 823 0 7 413 1,694 6,052 27.9 Berkshire 0 0 0 0 39 15 54 1,381 3.9 Bristol 0 33 8 0 2 54 97 632 15.3 Dukes and Nantucket .... 0 367 730 19 3 61 1,180 1,546 76.3 Essex 2 206 648 0 15 48 919 2,982 30.8 Franklin 35 0 0 0 40 35 110 583 18.9 Hampden 5 3 0 0 19 47 74 403 18.4 Hampshire 4 0 0 0 9 7 20 208 9.6 Middlesex 1 6 83 0 9 95 194 3,210 6.0 Norfolk 0 86 136 0 21 46 289 1,326 21.8 Plymouth 0 175 86 1 4 134 400 2,415 16.6 Suffolk 0 14 34 0 10 9 67 580 11.6 Worcester 1 0 0 0 50 88 139 2,166 16.5 Total 60 1,329 2,548 20 228 1,052 5,237 23,484 22.3 Table XV. Vectors of Equine Encephalomyelitis Per Cent of Adult Specimens which were Vectors. 49 1941.] HOUSE —No. 2260. Biting Habits. Table VIII, above, lists the adult mosquitoes captured on man. The vectors were represented as follows: Number. Per Cent. Aedes sollicitans 738 37.3 A. cantator 311 15.7 A. vexans 120 6.0 A. taeniorhynchus 12 0.7 A. triseriatus 3 0.2 A. atropalpus . . 0 0.0 Total vectors 1,184 59.9 Other aedes 198 10.0 All other genera 595 30.1 Total 1,977 100.0 Table IX, above, lists the adult mosquitoes caught in houses. Here the vectors were represented as follows: Number. Per Cent. Aedes cantator 66 1.8 A. sollicitans 56 1.8 A. vexans 44 1.4 A. triseriatus 19 0.6 A. atropalpus 12 0.4 A. taeniorhynchus 0 0.0 Total vectors 187 6.0 Other aedes 73 2.2 All other genera 2,870 91.8 Total 3,130 100.0 Of the 1,977 adults captured on man, 1,184, or 59.9 per cent, were vectors. Of the 3,130 adults caught in houses, only 187, or 6.0 per cent, were vectors. It has already been pointed out that the vast majority of the mosquitoes cap- tured on man are collected outdoors. Therefore it is at once apparent that the chances of a vector biting man are 50 HOUSE No. 2260. [Jan. about ten times as great outdoors as indoors. This informa- tion is important in protecting animals and man from un- necessary exposure to vectors during the outbreaks of the disease. Measures should be directed toward the removal of horses and mules from pastures and into screened stables. Children and infants, as well as adults, should be kept be- hind screens as much as possible, and not permitted to remain unprotected when outdoors where mosquitoes are prevalent. Unfortunately, the collections of mosquitoes on animals were so small that they are of no value. The 211 speci- mens which were captured in barns and stables may be an indication of the attraction of the vectors to horses and cattle. There were 33 vectors captured in barns; these were A. vexans 18, A. cantator 14 and A. sollicitans 1, form- ing 8.5 per cent, 6.6 per cent, 0.5 per cent of all mosqui- toes captured in these buildings. These numbers are too small to be conclusive. If the situation is analogous to man, then we may assume that whereas only 15.5 per cent of the mosquitoes captured in barns and stables were vec- tors, the vectors comprise a much larger per cent of the mosquitoes which bite animals outdoors. Vectors of Malaria. Numerical Importance. All of the Anopheles of Massachusetts may act as vectors of malaria. However, A. quadrimaculatus is the only im- portant one. A. maculipennis may transmit the plasmodia with greater effectiveness than A. punctipennis, but the latter is much more numerous and hence may play a greater r6le. A. crucians and A. walkeri are rare and hence are of no importance. The collection data on these vectors are summarized in Table XVI: 1941.] HOUSE No. 2260. 51 County. Anopheles. Total. CRUCIANS. MACULIPENNIS, PUNCTIPENNIS. 1 QUADRIMACULATU8. WALKERI. A. L. A. L. A. L. A. L. A. L. A. L. Barnstable - 5 0 0 2 41 4 21 1 - 7 67 Berkshire - - 0 11 42 830 29 57 1 8 72 906 Bristol - - 1 2 12 244 11 152 1 2 25 400 Dukes and Nantucket - - 0 0 0 5 0 0 0 - - 5 Essex . - 1 2 1 15 292 60 619 12 6 89 919 Franklin - - - 4 16 544 2 28 0 1 18 577 Hampden - - - 5 21 1,343 4 189 0 4 25 1,641 Hampshire - - - 2 3 146 5 9 - 1 8 158 Middlesex - - - 4 22 448 14 178 - 3 36 633 Norfolk - - - 2 2 129 20 117 2 2 24 250 Plymouth - 1 - 5 5 392 14 241 4 - 23 639 Suffolk - - - - 2 3 1 2 - - 3 5 Worcester - - 2 21 50 1,341 18 116 7 4 77 1,482 Total 0 7 5 57 192 5,758 182 1,729 28 31 407 7,582 Table XVI. Vectors of Malaria Distribution of Species by Counties (Collections). [A. = Adults; L. = Larvae.] 52 HOUSE —No. 2260. [Jan. The Anopheles comprised 16.9 per cent of the total col- lections, 19.3 per cent of the larvae, and 5.1 per cent of the adults. The largest numbers of collections of Anophe- les, 1,541 and 1,482, were made, respectively, in Hampden and Worcester counties. Since Worcester is a much larger county than Hampden, the Anopheles were more prevalent in the latter county. Very few collections were made in Dukes, Nantucket and Suffolk Counties. The small num- ber found in Suffolk County is easily explained because this county comprises the city of Boston and three other densely populated communities where mosquitoes are less likely to breed. Dukes and Nantucket Counties, on the other hand, are quite rural, and why Anopheles were collected in such small numbers has not been explained. Biting Habits. Anopheles were rarely captured on man outdoors. There were only 7 A. punctipennis and 2 A. quadrimaculatus among a total of 1,977 mosquitoes captured on man. It seems that these species are not serious offenders in the open. Of 3,130 mosquitoes captured in houses, A. quadri- maculatus comprised 13.0 per cent, A. punctipennis 1.5 per cent, A. maculipennis 0.9 per cent and A. walkeri 0.7 per cent, a total of 16.1 per cent. Anopheles prefer to bite man indoors, apparently. This observation may be con- trasted with the Aedes vectors of equine encephalomyelitis where the situation is reversed. Of a total of 211 mosqui- toes captured in barns and stables, 7 specimens (3.3 per cent) were Anopheles. Collections of mosquitoes on ani- mals were not attempted. It is therefore impossible to say that Anopheles are not attracted to animals, but the larger proportion of specimens captured in houses indicate that Anopheles prefer to bite man. Mosquitoes of Massachusetts. Genera. The order of Diptera is subdivided into a number of families; the particular family of flies to which all mos- quitoes belong is termed Culicidae. This family is composed 1941.] HOUSE —No. 2260. 53 of two subfamilies, the Culicinae and Chaoborinae. The members of the first subfamily are readily distinguished from the other by the presence in the female of a conspicu- ous proboscis adapted for bloodsucking. The Culicinae, or biting mosquitoes, are divided into two tribes, the Anoph- elini and the Culicini. The tribes, in turn, are divided into genera, and genera into species. The tribe Anophelini contains only one genus, the Anopheles. All the other genera of biting mosquitoes belong to the tribe Culicini. The name of a mosquito, as it is generally used, consists of the name of the genus and that of the species. Table XVII. —Relative Importance of the Genera of Massachusetts Mos- quitoes Per Cent of Adults and Larvae, by Specimens. Genus. Adults. Labvab. Total Relative Importance by Per Cent. Number. Per Cent. Number. Per Cent. Specimens. Aedea 8,124 46.1 9,504 53.9 17,628 6.6 Anopheles 1,177 4.1 27,423 95.9 28,600 10.6 Culex 7,401 3.4 207,650 96.6 215,051 78.7 Mansonia . 6,665 90.9 662 9.1 7,327 2.7 Psorophora 4 44.4 5 55.6 9 .0 Theobaldia 85 4.0 2,022 96.0 2,107 .8 Uranotaenia 19 .8 2,318 99.2 2,337 .8 Wyeomyia 9 36.0 16 64.0 25 0.0 Orthopodomyia 0 0.0 3 100.0 3 0.0 Total . 23,484 8.6 249,603 91.4 273,087 100.0 The relative numerical importance of these genera is determined by two methods. Table XVII lists the genera and the relative numerical per cent of the total mosquito fauna in Massachusetts. This per cent distribution is calculated on the basis of the specimens collected. In this evaluation the genus Culex represents 78.7 per cent of the mosquitoes, the genus Anopheles 10.5 per cent, and the genus Aedes only 6.5 per cent. The genera are broken down further into the number of larvae and adults collected, and the proportion of each to the total of the genus is expressed as a per cent. Among the specimens of Anopheles and Culex, larvae represented 54 HOUSE —No. 2260. [Jan. the vast majority. Among Aedes, however, adult speci- mens comprised almost a half of the total. The other genera were collected in much smaller numbers. Mansonia larvae, because of their peculiar adaptation in attaching themselves to plants, were collected very infrequently. The number of specimens per collection of adults and larvae is summarized in Table XVIII. The larvae aver- aged 6.35 specimens per collection, wdiich is more than twice the 2.94 average for adults. This difference in size of collections is due to two factors. The capture of a single adult often constituted a collection, while the larvae, usu- ally found in larger aggregates, afforded the gathering of a larger number of specimens in a single collection. Table XVIII. Average Number of Specimens per Collection. Genus. Larvae. Adults. Aedes 6.39 2.39 Anopheles 3.61 2.88 Culex 7.12 2.70 Mansonia 9.59 5.04 Psorophora 1.0 1.0 Theobaldia 7.17 1.35 Uranotaenia 3.34 1.5 Wyeomyia 8.0 9.0 Orthopodomyia 3.0 0.0 All genera 6.35 2.94 Seasonal Distribution Aedes mosquito collections were the most numerous when the survey began in July. Thereafter they con- tinued to decrease as the season progressed. Aedes com- prised over 50 per cent of all collections early in July, and less than 2 per cent late in August. Anopheles were most prevalent between the thirty-first and the forty-second week, that is, during August, September and early October, when this genus comprised 20 to 25 per cent of the col- lections. Culex continued to increase with the progress of the season, beginning with an initial 43 per cent in|'July and ending with 84 per cent in August. The seasonal curves are plotted in Graph 111. 1941.] HOUSE —No. 2260. 55 SEASONAL PREVALENCE OF GENERA MASSACHUSETTS 1939 CULEX ANOPHELES AEDES OTHERS Graph 111. 56 HOUSE —No. 2260. [Jan. Species. There are 56 species of mosquitoes in Massachusetts; 41 of these belong to the Culicinae, or biting mosquitoes. During the survey, 4 Culicinae and 2 Chaoborinae were col- lected in Massachusetts for the first time. Three species previously collected in the State were not included in the survey’s findings. The total collections, as well as the number of specimens of adults and larvae, are summarized in Table XIX. Table XIX is the presentation of data on the geographical distribution of the Culicinae. The figures indicate the number of collections made during the duration of the survey. Under each species the adults and larvae are considered separately. Dukes and Nantucket Counties are combined; these twro counties are islands off the south coast of Cape Cod, are small in size and have similar char- acteristics. 1941.] HOUSE —No. 2260. 57 Table XIX. Summary of Mosquitoes of Massachusetts. Larvae. Adults. Number of Specimens. Number of Collections. Number of Specimens. Number of Collections. Subfamily Culicinae. Aedes atropalpus 993 77 60 41 A. aurifer .... 0 0 642 186 A. canadensis . 495 122 770 301 A. cantator 2,704 399 1,326 600 A. cinereus 482 117 471 256 A. communis1 . 0 0 0 0 A. dorsalis 79 14 4 4 A. excmcians . 41 15 485 269 A. fitchii .... • 21 5 196 95 A. hirsuteron . 4 4 7 4 A. implacabilis 10 3 29 16 A. impiger1 0 0 0 0 A. intrudens 48 8 295 131 A. punctor 0 0 6 5 A. sollicitans 1,054 146 2,548 856 A. stimulans 8 2 59 38 A. taeniorhynchus . 112 17 20 8 A. trichurus 2 2 20 8 A. triseriatus . 92 33 228 158 A. trivittatus . 1 1 6 3 A. vexans .... 3,358 519 1,052 464 Total Aedes 9,504 1,484 8,124 3,433 Anopheles crucians 2 20 7 0 0 A. maculipennis 113 58 30 5 A. punctipennis 20,396 5,757 300 192 A, quadrimaculatus 6,810 1,729 790 182 A. walkeri 84 31 57 28 Total Anopheles 27,423 7,582 1,177 407 Culex apicalis . 78,944 13,051 1,746 688 C. pipiens 103,138 11,640 3,880 1,313 C. salinarius 2,215 922 832 339 C. territans 23,353 3,624 943 398 Total Culex 207,650 29,137 7,401 2,738 Mansonia perturbans 662 69 6,665 1,320 Orthopodomyia signifera2 3 0 0 0 Psorophora ciliata . 2 2 4 4 1 Not collected by survey. 2 Recorded by survey for the first time in Massachusetts. 58 HOUSE— No. 2260. [Jan. Labvae. Adults. Number of Specimens. Number of Collections. Number of Specimens. Number of Collections. Subfamily Culicinae. — Con. P. columbine1 3 3 0 0 P. posticata2 0 0 0 0 Total Psorophora 5 5 4 4 Tbeobaldia impatiens1 0 0 2 2 T. inornata 0 0 6 3 T. melanura 1,971 265 70 52 T. morsitans 51 17 7 6 Total Tbeobaldia 2,022 282 85 63 Uranotaenia sapphirina . 2,318 693 > 19 12 Wyeomyia smithii .... 16 2 9 1 Total culicinae .... 249,603 39,254 23,484 7,978 Subfamily Chaoborinae.3 Chaoborus 37 20 41 16 C. albatus - - - - C. albipes 5 2 0 0 C. americanus - - - - C. punctipennis .... - - - - C. trivittatus - - - - Total Chaoborus 42 22 41 16 Corethrella brakeleyi3 14 5 0 0 Dixa 195 84 11 6 D. centralis - - - - D. clavata - - - - D. cornuta - - - - D. modesta - - - - D. notata - - - - Total Dixa .... 195 84 11 6 Eucorethra underwoodi1 . 3 3 0 0 Mochlonyx 24 11 0 0 M. cinotipes - - - - M. fuliginosus - - - - M. karnerensis ..... - - - - Total Mochlonyx 24 11 0 0 Total Chaoborinae 278 125 52 22 Grand total .... 249,881 39,379 23,536 8,000 1 Recorded by survey for the first time in Massachusetts. 2 Not collected by survey. 3 Species not routinely identified by survey. Table XIX. Summary of Mosquitoes of Massachusetts Concluded. 1941.] HOUSE— No. 2260 59 Aedes. County. ATRO- PALPUS. AURIFER. CANA- DENSIS. CANTATOR. CINEREU8. DORSALIS. EXCRU- CIANS. FITCHII, HIR- 8UTERON. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. Barnstable 6 - 64 - 92 21 163 184 41 50 2 10 87 3 58 5 2 1 3 - 4 3 - - 9 3 - - 1 - 2 - - - Bristol - - 5 - 5 7 14 39 13 - - - 1 1 - - - - Dukes1 - - 1 - 8 3 168 112 10 17 - 1 4 - 2 - - 2 Essex 2 8 10 - 23 2 129 11 39 1 - 1 42 - 12 - - - Franklin 26 29 1 - 8 1 - - 2 - - 1 2 - 1 - - - Hampden 4 35 5 - 15 2 1 - 6 - - - 7 1 1 - - - Hampshire 1 10 4 - 2 - - - 3 - - - 4 1 1 - - - Middlesex 1 - 12 - 14 2 4 12 20 4 - - 24 1 3 - 1 - Norfolk - - 10 - 26 73 14 6 15 20 1 - 23 5 4 - 1 1 Plymouth 63 - 57 6 100 28 28 8 1 1 37 2 9 - - - Suffolk 1 - 1 1 7 7 3 1 - - 1 - - - - - Worcester 1 - 7 - 46 1 - - 67 13 - - 36 1 2 - - - Total 41 77 186 0 301 122 600 399 256 117 4 14 269 15 95 5 4 4 1 Includes Nantucket. Table XX. Mosquitoes of Massachusetts, by Counties'—Collections. (A. = Adults; L. = Larvae.] 60 HOUSE —No. 2260 [Jan, County. Aedbs. IMPLAC- ABILI8. INTRU- DEN9. FUNCTOR. SOLLICI- TANS. 8TIMULAN8. TAENIOR- HTNCHUS, TRICH- URUS. TRI- 8ERIATU9. TRI- VITTATU8. VEXANS. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. Barnstable 7 - 51 3 4 - 196 48 19 2 - - 6 - 5 - 1 - 126 167 Berkshire - - 3 - - - - - - - - - - - 12 2 - - 12 69 Bristol - - - - - - 7 2 - - - - - - 2 2 - - 35 21 Dukes1 - - 1 - - - 290 70 1 - 7 17 - - 3 - - - 31 30 Essex 1 1 11 - - - 260 3 5 - - - - - 14 - - - 31 11 Franklin - - 2 2 - - - - 1 - - - - - 33 2 - 1 21 24 Hampden - - 3 - - - - - 1 - - - - 1 13 7 - - 23 40 Hampshire - - 3 - - - - - 1 - - - - - 9 1 - - 0 39 Middlesex - - 7 - - - 16 4 1 - - - - - 8 1 - - 27 17 Norfolk 1 - 8 1 - - 30 4 - - - - - - 13 9 - - 26 7 Plymouth 1 - 22 - 1 - 46 14 4 - 1 - 1 1 4 3 1 - 60 60 Suffolk - 1 2 - - - 10 1 1 - - - - - 6 - - - 8 2 Worcester 6 1 18 2 - - 1 - 4 - - - 1 - 36 6 1 - 48 42 Total 16 3 131 8 5 - 856 146 38 2 8 17 8 2 158 33 3 1 454 519 1 Includes Nantucket. Table XX. Mosquitoes of Massachusetts, by Counties Collections Continued. [A.“Adults; L.“Larvae.] 1941.] HOUSE— No. 2260. 61 County. Anopheles. CuLEX. CRUCIANS. MACULI- PENNIS. PUNCTI- PENNIS. QUADRI- MACULATUS. WALKER I. APICALIS. PIPIEN8. 8ALINA- RIUS. TERRITANS. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. Barnstable - 5 - - 2 41 4 21 1 - 17 1,542 44 353 24 92 6 80 Berkshire - - - 11 42 830 29 57 1 8 61 1,013 143 1,087 31 32 76 1,168 Bristol - - 1 2 12 244 11 152 1 2 12 577 33 688 19 75 6 98 Dukes1 - - - - - 6 - - - - 7 393 26 470 12 251 10 101 Essex - 1 2 1 16 292 60 619 12 6 24 654 63 1,435 22 137 29 409 Franklin - - - 4 16 544 2 28 - 1 68 601 139 794 36 38 31 295 Hampden - - - 5 21 1,343 4 189 - 4 8 821 33 325 2 7 9 130 Hampshire - - - 2 3 146 5 9 - 1 6 540 13 464 3 5 7 236 Middlesex - - - 4 22 447 14 178 - 3 347 1,536 391 3,188 96 105 103 476 Norfolk - - - 2 2 129 20 117 2 2 4 404 69 1,230 12 79 25 271 Plymouth - 1 - 6 5 392 14 241 4 - 38 2,203 50 515 12 57 9 54 Suffolk - - - - 2 3 1 2 - - 5 8 61 340 12 7 15 8 Worcester - - 2 21 50 1,341 18 116 7 4 91 2,759 248 871 58 37 72 198 Total 0 7 5 68 192 5,757 182 1,729 28 31 688 13,051 1,313 11,640 339 922 398 3,524 1 Includes Nantucket. Table XX. Mosquitoes of Massachusetts, by Counties Collections Continued. [A. = Adults; L. = Larvae.) 62 HOUSE— No. 2260. [Jan, Mansonia. PsOROPHORA. Theobaldia. Urano- TAENIA. Wybomyia. County. PER- TURBANS. CILIATA. COLUMBIAE. IMPATIENS. INORNATA. MELANURA. MOR- SITANS. SAP- PHIRINIA. SMITHII. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. A. L. Barnstable . 337 61 5 99 - 4 1 49 _ 2 Berkshire 34 - - - - - - - - - - - 1 _ 1 39 1 _ Bristol 25 - - - - - - - - - - 10 _ _ - 42 _ _ Dukes1 31 - 1 - - - - - - - 1 71 _ 2 _ 1 _ _ Essex . 209 - - - - - 1 - - - 5 1 3 1 _ 55 - - Franklin 11 - 1 - - - - - - - 4 1 - _ - 3 - _ Hampden . 49 1 2 - - 1 - - - - 2 4 _ - _ 60 - Hampshire . 12 - - 2 - 2 - - 1 - - - _ - _ 30 _ _ Middlesex . 71 - - - - - - - - - 8 5 - 6 5 120 - - Norfolk 146 4 - - - - - - - - 5 12 - 1 - 64 _ _ Plymouth . 224 1 - - - - - - - - 7 50 2 2 2 173 _ - Suffolk 18 - - - - - - - - - 1 1 - _ - _ _ _ Worcester . 153 2 - - - - 1 - 2 - 14 11 - 1 3 57 - - Total 1,320 69 4 2 - 3 2 - 3 - 52 265 6 17 12 693 1 2 1 Includes Nantucket, Table XX. Mosquitoes of Massachusetts, by Counties Collections Concluded. [A, = Adults; L. = Larvae.] 1941.] HOUSE No. 2260. 63 Public Health Importance of Aedes Species. This survey was instituted because of the possible future recurrence of equine encephalomyelitis in the State. Since only Aedes mosquitoes apparently transmit the virus of the disease, a short resume of the possible public health impor- tance of each species of the genus is given below. Only 6 of the 23 have as yet been shown to transmit the virus, but others will undoubtedly be added to the list. Aedes atropal-pus. This species has been demonstrated to transmit equine encephalomyelitis in the laboratory. Of the six vectors known to exist in Massachusetts, it is about fourth in numerical importance, comprising 7.77 per cent of the specimens of vectors. It was collected from three portions of the State, the Connecticut Valley, Essex County and Cape Cod. In favorable years its distribution may be more widespread. The mosquito breeds principally in clear water accumu- lated in rock formations, as in rivers, streams, ponds, lakes, marshes and swamps. It prefers sparsely populated areas. A few adults, not avid biters, were collected in houses and stables. The adults are prevalent during August and September. However, due to the peculiar geographical distribution, and to the small number of A. atropalpus, this species could not have played a large role in the 1938 outbreak of equine encephalomyelitis. It is probably not an important natural vector of the disease. Aedes aurifer. This species may be of no public health importance, as it has not yet been proven to be a vector of disease. However, it is one of the species which bites man freely. Its distribution was widespread throughout the State. All collections consisted of adults, and no larvae were found. Matheson has had the same experience in Central New York, where adults are abundant and larvae have not been collected. The adults are apt to bite in the open and do not enter buildings as frequently as many of the other species. The adults are most prevalent early in the summer, and by August and September are comparatively rare. 64 HOUSE —No. 2260. [Jan. Aedes canadensis. This mosquito is not a proven vector of disease, but is important as a nuisance. The species is widely distributed throughout the State. Larvae were collected in small numbers, mainly in ponds and lakes, running and still water, and marshes and swamps in thinly settled regions. Although not übiquitous, the larvae are found in many different types of breeding places. The adult bites man in the open, but does enter houses at times. The species is most numerous in the early summer; by July it is decreasing in number, and in August and September becomes rare. Aedes cantator. As a vector of equine encephalomyelitis, this species may be of great public health importance. Numerically, it is in first place among the vectors of equine encephalomyelitis in number of collections, and in second place in number of specimens. It is a salt marsh mosquito and limited, in geographical distribution, to the coast and adjacent regions. Usually the adults were within ten miles of the nearest salt water; rarely were they found fifteen miles from their breeding places. The larvae were collected in largest numbers from coastal marshes and swamps, and streams and rivers. Dumps, cranberry bogs and barrels were the most frequent man-made breeding places. The adults bite man principally in the open, but enter houses as well, although in much smaller numbers than certain other mosquitoes. They have been collected in houses, barns and stables, and in the vicinity of horses and birds which are known to be susceptible to equine encephalomye- litis. The species was most numerous in September and October, when these adults represented 15 per cent of the total adult collections. This mosquito is one of the three most numerous vectors of the virus of equine encephalomyelitis. Its seasonal distri- bution coincides with that of the disease. Although the geographical distribution is not entirely the same, the mosquito was collected from some parts of the area where the outbreak occurred, namely, in Bristol and Plymouth Counties. Aedes cinereus. This Aedes mosquito is not a proven 1941.] HOUSE —No. 2260. 65 vector of disease, but it is a fierce biter. It is distributed throughout the State, but largest collections were made in the eastern portion. The larvae were found most fre- quently in marshes and swamps and in running and still water, in less thickly settled areas. Although the adults bite man in the open, the mosquito has been collected in houses, barns and stables. Some adults were collected from a horse, and still others were caught in the vicinity of cattle, horses and mules. The adults were caught in largest num- bers early in the season, and gradually decreased throughout the summer and autumn. Larvae were collected as late as September, although not to a great extent. This species may be a nuisance early in the spring, but is probably of no importance as a vector. Aedes communis. This species was reported by John- son in 1925 as found in Massachusetts. However, it was not collected during the survey. Matheson states that the adults appear early in spring and persist until late in the season. He collected the larvae from spring pools, swamps and marshes. This species is probably very unimportant, as it was not picked up in the 49,000 collections made dur- ing the survey. Aedes dorsalis. This species is one of the rarer Aedes mosquitoes. It is not an important biter and is not known to transmit the eastern virus, though it does transmit the western virus of equine encephalomyelitis. Scattered col- lections were made in Franklin County in the west, and along the coastal region in the east. Insufficient collections of larvae were made to ascertain the typical breeding places of this species, and the adults were collected even less fre- quently. One collection of this species was made on man. The species is apparently most abundant early in spring, becomes rare in July, and remains so for the rest of the season. Aedes excrucians. This mosquito is of little importance as a biter. It was found to be state wide in distribution. The larvae were collected in small numbers; two collec- tions were made in cranberry bogs and one in a dump. The adults bite man and were collected in houses, barns and 66 HOUSE —No. 2260. [Jan. stables. The adults appeared early in spring and were rare by September. In spring this species may be a nui- sance outdoors in certain districts. Aedes fitchii. Little concern is expressed over this mos- quito, as it is not a fierce biter and probably plays no role in the spread of disease. This species was collected in scat- tered areas throughout the State. Adults, wdiich were col- lected on man and in houses and barns, were found only during the early part of the season. Larvae were found in very small numbers. The species is definitely a spring and early summer mosquito. Aedes hirsuteron. This species is quite rare in Massa- chusetts. Small collections were made along the coastal regions. Aedes hirsuteron is of no public health importance, as it seldom bites man and occurs in small numbers. The seasonal prevalence of this species cannot be determined from the collections made during the survey. Aedes impiger. This species was not collected by the survey. Johnson reported it from Massachusetts in 1925. It is rare and little is known about its habits. It is, there- fore, an unimportant mosquito. Aedes implacabilis. This is another rare species of Aedes. The adults were collected during July and August, and the larvae were found in small numbers throughout the season. It is an early mosquito, with a spring and early summer predominance. The mosquito is unimpor- tant, as it is a rare species, is not a fierce biter, and is not known to transmit disease. Aedes intrudens. Since this species bites man in the open it may be important as a nuisance. It was distrib- uted throughout the State. Larvae were collected in small numbers from cranberry bogs, cesspool overflows and dumps. The adults were captured in houses and on man. The mosquito was most numerous in the early summer and became rare in August and September. Aedes punctor. This is a rare species of which only adults were collected. These collections were made in Plymouth and Barnstable Counties. One collection of adults was made in a house. It is an unimportant mosquito. 1941.] HOUSE No. 2260. 67 Aedes sollicitans. This salt marsh mosquito, a fierce biter, is one of the most numerous of the vectors of the virus of equine encephalomyelitis. Geographically, it is limited to the vicinity of salt or brackish water. The adults were rarely collected more than fifteen miles from the nearest salt water. Larvae were collected in largest num- bers from marshes and swamps. Of all species, Aedes solli- citans was captured most frequently on man. It was col- lected in houses with the same frequency as Aedes cantator, but less frequently in barns and stables. Collections of adults were made in the vicinity of horses, mules, cattle and birds which are susceptible to equine encephalomyelitis. This species was most numerous in August and Septem- ber. This seasonal prevalence coincides with that of the disease. As in the case of Aedes cantator, the geographical limitation of this mosquito was not the same as that of the disease in 1938. However, mosquitoes were much more prevalent during the outbreak, and this species may have been present in 1938 in areas in which it was not found in 1939. Aedes stimulans. This mosquito is not known to transmit disease; it is not a fierce biter and is numerically unimportant. Larvae were collected in scattered areas throughout the State. Adults were captured on man in two instances; a collection was made in a stable and in a house. This species predominates in the spring and by August is quite rare. Aedes taeniorhynchus. This southern salt marsh mos- quito is a vector of equine encephalomyelitis. It is a fierce biter, but occurs in such small numbers and is so limited in geographical distribution that it is not of any great public health importance. Its collection was limited to the island of Martha’s Vineyard and to the Buzzard’s Bay region of southern Massachusetts. Larvae were found in marshes and swamps. Since most of the adults were captured on man outdoors, this species probably does not frequent houses. The adults were captured in August and Septem- ber, and it is apparent that the species is most numerous at this time. 68 HOUSE —No. 2260. [Jan. It is very unlikely that Aedes taeniorhynchus played a role in the 1938 outbreak of equine encephalomyelitis, unless its distribution extended farther northward in 1938 than it did in 1939. Aedes trichurus. This is a rare species which is un- important as a nuisance and as a public health menace. This mosquito was collected so infrequently that no con- clusions concerning its life habits can be made. It is prob- ably an early mosquito with a spring predominance. Aedes triseriatus. Laboratory experiments have demon- strated that this species can transmit equine encephalo- myelitis. It was found to be state wide in distribution, but was less numerous than Aedes vexans which is another vector of this disease. The larvae were collected from barrels, wells, dumps and water troughs. Adults were captured in houses more frequently than on man. Collec- tions were made as frequently in thickly settled areas as in rural sections. The species was most numerous in Au- gust and the first three weeks of September, but decreased rapidly during the last week of September. Aedes trivittatus. This is a rare species of very little importance; Aedes trivittatus larvae were collected in two towns and adults in three. Since collections were so few it is impossible to draw any conclusions as to the life habits or seasonal predominance. Nine adult specimens were collected in houses; one collection was made in the vicinity of cattle and two in the vicinity of horses. Aedes vexans. This species, a demonstrated vector of equine encephalomyelitis, is state wide in distribution and one of the most numerous of the vectors. The larvae are übiquitous in their breeding habits; collections were made from marshes, swamps, ponds, lakes, streams, rivers, cran- berry bogs, puddles, dumps, barrels, a water trough, a well and a rocky crevice. The adults are fierce biters and were frequently collected on man, in stables, barns and in houses. Although more collections were made in rural areas, urban communities were not without this mosquito. This species was collected more frequently in barns and stables than any other Aedes. It was also captured in the 1941.] HOUSE— No. 2260. 69 vicinity of horses, mules, cattle and many kinds of birds. Aedes vexans was the most prevalent in August and Septem- ber. It was present in large numbers in July, and probably would have been present in larger numbers were it not for the drought in June and July. It is conceivable that this species was involved in the 1938 outbreak of equine encephalomyelitis. It is the only numerous vector that was found in all areas where the disease occurred. In fact, its distribution was far more extensive than the area involved in the outbreak. It was the most numerous of the vectors if the number of speci- mens is considered, and second most numerous on the basis of collections. It is not unlikely that Aedes vexans may prove to be the most important natural vector of equine encephalomyelitis. Summary and Conclusions. 1. The information regarding mosquito breeding col- lected in this survey should be valid for many years. Breeding habits of these insects are well stabilized, and changes develop very slowly. There is likewise little pros- pect that large works which will affect mosquito breeding, such as the development of the Quabbin Reservoir in the Swift River Valley, will be undertaken in the near future. 2. While this survey was made in a dry year, it is be- lieved that differences which result in wet years will be largely quantitative rather than qualitative. The available places for breeding will be both larger and more numerous, and water collections will persist for periods long enough for larvae to develop into the adult stage. 3. The difficulty experienced in collecting larvae in the salt marsh areas, where control work under the supervision of the Reclamation Board is being done, gives assurance that this control work is proving effective where the ditches are well laid out and maintained. 4. There is reason to believe that horse sleeping sickness might have been more prevalent in the salt marsh areas in 1938 if these salt marsh mosquitoes, most of which have been shown to be able to transmit the virus, had been as 70 HOUSE— No. 2260. [Jan. 1941. numerous as they were previous to 1930 when the control work was begun. 5. The problem of the control of fresh-water mosquitoes is much more difficult than the control of salt-marsh mos- quitoes. The breeding places are not only more numerous, but there is a great diversity in the types of water collec- tions. Control measures are both more difficult to plan and carry out and more costly to execute. Because of the expense, it will not be feasible to undertake extensive con- trol except when some disease, such as horse sleeping sick- ness, is being spread by fresh-water mosquitoes. In such cases the control measures should be aimed at the species known to be responsible for the spread. This survey was undertaken to collect information to form the basis for directing such efforts when and if the need arises. 6. Because no large scale control measures of fresh-water mosquitoes have ever been undertaken in this State, and because it seems likely that Aedes vexans, a fresh-water mosquito, was responsible for the spread of horse sleeping sickness (equine encephalomyelitis) in 1938, control work on an experimental basis should be undertaken in selected areas to discover what methods will prove most effective for the types of breeding places in this region. Such work might well be undertaken, under the supervision of the Reclamation Board, in areas where mosquitoes have been pests, such as the Charles River Valley, or in areas where the control works may be partly justified by land reclama- tion or other reasons, such as the draining of the Hocka- mock or Great Cedar Swamp in Easton, Taunton and surrounding towns. Respectfully submitted, ROY F. FEEMSTER, M.D., De.P.H., Director, Division of Communicable Diseases. VLADO A. GETTING, M.D., Dr.P.H., Technical Director of Mosquito Survey.