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HomeMy WebLinkAbout1980-03-31-PCAC-rpt.pdf MOSQUITO CONTROL IN LEXINGTON INTERIM REPORT OF THE PEST CONTROL ADVISORY COMMITTEE TO THE LEXINGTON BOARD OF SELECTMEN MARCH 31, 1980 COMMITTEE MEMBERS: John W. Andrews, Chairman Ann Bond Ray Gabler Barbara Green Paul Rif fin Martin white 1 28 March 1980 To: Lexington Board of Selectmen From. Pest Control Advisory Committee Subject: Interim Report on Mosquito Control in Lexington The Pest Control Advisory Committee has spent a productive few weeks examining previous mosquito control efforts in Lexington, looking at the results of mosquito control reviews in nearby towns, reviewing technical and scientific literature on pesticides, talking to personnel involved in organized mosquito control projects, and analyzing the options available to Lexington. Although several questions remain to be investigated before our final report will be complete, certain important initial conclusions are emerging and have formed the basis of this report. The final decision concerning the type of mosquito control program to be implemented in Lexington must be made by the Board of Selectmen in conjunction with the Lexington Town. Meeting. This Committee will make certain recommendations, but will present information which will be useful regardless of the ultimate decision. The Committee would appreciate inputs from any person concerning errors or omissions noted in this report or additional information which should be considered in preparation of our final report. John W. Andrews, Chairman Ann Bond Ray Gabler Barbara Green Paul Riff in Martin White Tr INTERIM REPORT OF Jai: PEST CONTROL ADVISORY COMMITTEE MOSQUITO CONTROL IN LEXINGTON CONTENTS Glossary of Terms Measurements Summary of Principal Findings Summary of Principal Recommendations 1.0 Discussion of Findings 2.0 Discussion of Program Options 3.0 Recommendations for 1980 4.0 Recommendations for the Future APPENDICES A. The Decision-making Process. Mosquito Control and Controversy B. Biology of Mosquitoes C. Mosquitoes and Public Health D. Risks Involved in Human Pesticide Exposure E. Pesticide Use Planning and Monitoring F. East Middlesex Mosquito Control Project G. Effectiveness of Organized Mosquito Control Efforts H. Mosquito Adulticiding Practices I. Effects of Pesticides on Non-target Organisms REFERENCES GLOSSARY OF TERMS acute effect - A toxic effect which appears, usually within hours, following a single exposure to a toxic substance adulticide - A material applied to control adult forms of mosquitoes. application - The introduction of a pesticide into an area in order to control pest species. benthic Living in the mud or sediment under a body of water. biological control - Pest control obtained by introducing biological agents (predators, parasites, or pathogens) into the environment broad-spectrum pesticide - A pesticide which has toxic effects on a wide range of pest species. carcinogenic - Capable of causing cancer. cholinesterase - An enzyme essential to the proper transmission of impulses in the nervous systems of many species. chronic - Resulting after exposures over an extended period of time (perhaps years) Eastern Equine Encephalitus (EEE)-A virus disease. transmitted by certain species of mosquitoes. EC„ - Effective concentration 50% : The concentration of a toxic substance which produces toxic effects in 50% of the organisms exposed. epidemiology - The study of the statistics of occurence of effects in a population of organisms and the means by which diseases spread. entomology - The study of insects. half-life - The time period in which one-half of a material degrades. heartworm - A parasite in dogs which is transmitted by mosquitoes. immune response - The response by which the body resists invasion by disease organisms or cancer cells. insecticide - A material used to kill insects. May be either chemical or biological in origin. integrated control - A control approach in which two or More control methods are used in a coordinated manner to reduce losses to: pest species. 1 GLOSSARY (continued) larvicide - A material employed to control larvae of mosquitoes - Lethal concentration 50% : The concentration of a toxic substance --Jv which is lethal to 50% of exposed organisms. LD 50 - Lethal dose 50% : The dosage of a toxic substance which is acutely lethal to 50% of exposed organisms. natural control - Control which results from agents or conditions which occur naturally in the environment non-target organisms - Organisms which share the environment with the pest species but which the application is not intended to control organochlorine insecticide - A synthetic organic insecticide whose chemical composition includes chlorine. Examples: Methoxychlor, DDT, Chlordane,etc. organophosphate insecticide - A synthetic organic insecticide whose chemical composition includes phosphorus. Examples include malathion, Dibrom, Abate, parathion, etc. parasite - A plant or animal which feeds in or on another living plant or animal in a manner which is detrimental to the host. 1 pesticide - A substance applied to kill a pest species. - A logarithmic measure of the acidity of water. pH values less than 7 correspond to acidic solutions. predator - An animal which feeds upon other animals. pre-hatch application -An application of pesticide applied before eggs of the pest species have hatched. residual effect - The ability of a pesticide to kill pests for some significant period of time after the application. selective pesticide - A pesticide which affects primarily target species and tends to do no harm to non-target species. target species - The pest species which a pest control measure is intended to control 2 a GLOSSARY (continued) teratogenic - Capable of causing birth defects.. Threshold Limit Value - An industrial exposure standard - the concentration considered-acceptable for daily exposure of nearly all workers. TLm - Mean tolerance level, approximately equivalent to LD50. toxic - Having chemical properties which are injurious to plants animals, or human beings ultra-low volume (ULV) - A method of applying a pesticide which involves application of a concentrated aerosol at low volumes. (rather than application of a dilute mixture at higher volumes) . MEASUREMENTS 1 fluid ounce = 29.6 ml = 1.805 cu. in. 1 cu. meter = 1000 liters = 106 cm. 1 gallon = 0. 1337 cu. ft. = 3.785 liters 1 meter = 39.37 in. 1 fluid ounce/acre = 0.00731 ml/m2 1 ppm in H2O = 1 mg/L 1 acre = 43560 sq ft. = .4047 hectare = 4047 m2 3 6 4 i_ SUMMARY OF PRINCIPAL FINDINGS 1. Mosquito control in Lexington is not required for public health reasons - the focus of the program has been and should continue to be nuisance abatement. 2. There are a variety of techniques which can be applied to reduce mosquito nuisance. Among these are elimination of breed- ing habitat, strengthening of natural controls, personal protection measures, use of larvicidal pesticides, and use of adulticidal pesticides. 3. A small but non-zero risk exists when people are exposed to pesticides in mosquito control operations. A well-designed program will seek to minimize or eliminate human exposure and to respect requests for non-exposure 4. There is no factual evidence that previous mosquito control efforts have had any significant impact upon mosquito densities in Lexington, although short-lived local reductions have been observed in adulticiding operations. In some cases a question exists as to whether pesticide use may have resulted in an increase in numbers of mosquitoes by destruction of natural checks upon mosquito numbers. 5. Additional planning and monitoring is advisable in pursuit of safe and effective use of pesticides in mosquito control operations. Currently neither the Town nor East Middlesex Mosquito Control Project are capable of implementing the required safeguards. 6 There are a number of nuisance abatement actions which can be taken through coordination of existing Town resources. 4 SUMMARY OF PRINCIPAL RECOMMENDATIONS 1. There should be a moratorium on the use of broad—spectrum chemical insecticides until better means of controlling and monitoring their effects can be devised. 2. The Town should pursue non-toxic nuisance abatement techniques which take full advantage of existing Town resources and the cooperation of private citizens. 3. Any future use of chemical pesticides should complement, not replace, non-toxic nuisance abatement measures. 5 1. Discussion of Interim Findings 1. 1 Mosquitoes as Nuisances The status of mosquitoes as nuisance insects in the Town of Lexington has engendered in many citizens a legitimate desire to find means to reduce or nullify their nuisance potential. Two avenues are open: to reduce the population density of mosquitoes in the environment and to reduce the potential for bites from mosquitoes which do occur. Both government and the individual must share responsibilities in pursuing these objectives. 1.2 Realistic Expectations Realistic expectations are important in evaluating mosquito control options. Effectiveness figures quoted from mosquito control project reports have given many residents the mistaken impression that most if not all mosquitoes can be eliminated by a modest investment in organized mosquito control. This is simply not the case. Last Spring the mosquito population levels in Lexington were extremely high and mosquito nuisance reports were received from all sections of Town. This occurred despite an ongoing, mosquito control program and an increase in the rate of adulticiding, spray operations in comparison with the previous year. Town investments in t:'osquito control must be made in the awareness that the results to be effected are limited and that in many cases individual efforts will prove more effective than government programs. 1.3 Mosquitoes as a Public Health Problem The only mosquito-borne disease which is considered to be a significant public health problem in Massachusetts is Eastern Equine .Encephalitus (EEE). This disease is largely confined to Bristol .and Plymouth Counties, and even 6 b there years may pass without a human case being recorded. There is no evidence that the disease has ever occurred in Lexington or in nearby towns without organized mosquito control programs. Hence the expenditure of Town funds for prevention of EEE in Lexington does net appear to be warranted. Should any health-related expenditures be made in the future, the nature of the program should be determined in conjunction with the Massachusetts Department of Public Health since they have responsibility in this area. In general, nuisance abatement programs are not conducted according to sound principals of medical entomology. See Appendix C for further discussion. 1.4 Pesticide Risks for Human Health Pesticide use in mosquito control in Lexington has conformedto government standards for the materials employed. These standards provide a certain measure of protection against known adverse effects of materials upon human health. However many gaps exist in the scientific knowledge concerning effects of even the best known pesticides. It is quite possible that subtle, rare, or unrecognized injuries are occurring now or will appear in the future. Rather than viewing a given instance of pesticide use as simply "safe" or "unsafe" , it is more realistic to view pestice use as a matter of calculated risk. If the benefits to be derived from pesticide. use outweigh the risk involved, then the use is justified. The probability of pesticide-related injury increases with the number of persons exposed, the frequency of exposure, the dosage, and the number of different pesticides used. Proper program design requires minimizing the above risk factors. Unmonitored pesticide use or pesticide overuse due to failure to consider alternative control techniques is to be avoided. See Appendix D for further discussion. 7 0 1.5 Ecological Effects of Mosquito Control Techniques The pesticides of choice in mosquito control project efforts are broad-spectrum materials which are toxic to a wide variety of organisms. Both lethal and sub-lethal effects may cause declines in natural populations of animals. Effects are likely to be limited to the area of application or to aquatic environments directly downstream. Beneficial insects (bees, ladybeetles, praying mantis, mite predators, etc.) are likely to be injured. This can result in secondary pest outbreaks. Fish are highly susceptible to injury. Bird populations are not likely to suffer from most pesticides currently in use unless the total insect population is suppressed while nestlings are being fed. Certain larvicidal materials (such as Altosid, Flit MLO,. and Bacillus thuringiensis) appear to have much less potential for ecological disruption. So far,however,their use in organized mosquito control work in Massachusetts has been quite limited. See Appendix I for further discussion. 1.6 Effectiveness of Previous Pesticide Use in Lexington Substantial questions have arisen concerning the level of benefits derived from previous pesticide use in Lexington by the East Middlesex Mosquito Control Project (EMMCP) Only a small fraction of potential mosquito breeding areas have been subjected to even a single treatment with larviciding agents. Adulticiding operations have covered only small areas of Town and, due to their short-lived effectiveness, have had little impact upon the average number of mosquitoes Counterproductive results are also of concern when pesticides are applied in a manner which allows mosquito populations to recover between applications. Because the materials used are toxic to natural control agents, the recovery of the pest population may exceed the level which would have existed without pesticide use. The question of the role of natural controls should be resolved in order to determine the actual level 8 rt, of benefits resulting from pesticide applications. Better measures and means for evaluating program effectiveness are also desirable so that the Town can know exactly what level of nuisance abatement it is getting for its money. - Further discussion of the effectiveness of mosquito control techniques can be found in Appendix G and Appendix H. 9 ct, 2 0 Discussion of Mosquito Control Program Options 2. 1 Informal Programs One obvious option available to the Town is to have no formal mosquito control program. Certain nearby towns (such as Concord and. Lincoln) have chosen this route. In such cases some nuisance abatement actions are undoubtedly undertaken by individuals or Town agencies. The efficiency of these actions probably varies widely depending upon the individuals involved and the extent to which they are aware of the nuisance abatement actions which are within their power. Control actions which require significant expense or planning are unlikely to be undertaken. This option involves little expense or pesticide problems for the town, but it may mean that certain nuisance problems which could be resolved will persist due to lack of attention. 2.2 Formal Program Options In considering options for establishment of a formal mosquito nuisance abatement program, it is helpful to divide the abatement techniques into four categories as described below. Category A: Baseline Nuisance Abatement. This category includes those non-pesticide techniques which provide a constant suppression of the base number of mosquitoes in the environment or which provide continual protection against the nuisance potential of existing mosquitoes. Among such techniques are source reduction (ditching and draining, removal of water containers, etc.) , strengthening of natural controls, water quality management, and personal protection. These approaches are discussed further in section 3. Category B: Preferred Substance Larviciding. There are currently available certain larvicidal materials which are essentially free of hazard to human and are unlikely to significantly affect non-target populations. Among such products are Altosid (methoprene) , Flit MLO (larvicidal oil) , and bacterial larvicides. An increasing number of biological agents are appearing which 10 !!Z will be added to this list in the future. Category C: Chemical Larviciding These techniques involve the use of chemical pesticides (such as organophosphates or organochlorines) in the aquatic environment. These materials can affect a wide range of non—target organisms and may have degradation products which are themselves toxic in various ways. The ecological impact and the potential for human exposure are dependent upon exactly where the materials are applied and upon the hydrology of the target area. Category D: Chemical Adulticiding. These techniques involve the spraying of insecticide (usually organophosphates) into the air in order to kill adult mosquitoes. These techniques generally result in unavoidable impact upon non-target organisms and in unavoidable exposure of humans to the pesticide. Techniques in categories C and D raise many more questions concerning potential unintentional effects than do categories A and B. The level of planning and monitoring required for the chemical approaches is therefore much greater. Appendix E to this report discusses some advisable safeguards and Appendix I discusses ecological effects which should be monitored. Currently it appears that neither the Town nor the Mosquito Control Project have the personnel, resources, or program structure necessary to adequately address concerns resulting from the use of broad-spectrum chemical pesticides. 2.3 Benefits to Be Derived from Nuisance Abatement Programs In the judgement of the Committee, all programs which involve modest expenditures will, regardless of the techniques employed,yield only slight 1 For instance, East Middlesex Mosquito Control Program has no public education program, does no pesticide residue monitoring, does not monitor non-target organisms, provides no special medical examinations to employees, handling pesticides, and is not subject to any detailed professional progarm review. They have no professional staff member available for summer biological surveys (their superintendent must devote his time primarily to supervising pesticide applications) . 11 reductions in Town-wide mosquito densities. In years of repeated heavy rains, substantial numbers of mosquitoes will almost certainly appear despite control attempts. Furthermore some level of mosquito nuisance is inevitable for housing placed in moist forested areas. However nuisance abatement measures can solve spot problems (e.g. by eliminating mosquito breeding at an isolated site near residences) . Measures may also result in a modest reduction in mosquito numbers below those which would otherwise result from a given level of rainfall. A program can also provide guidance to citizens in avoiding bites from existing mosquitoes and in avoiding the inadvertent creation of mosquito breeding sites. 12 3.0 Recommendations for 1980 The planning, monitoring, and biological knowledge required to ensure the safe and effective use of broad-spectrum chemical pesticides in mosquito control efforts in Lexington does not now exist. Hence the Committee recommends that a moratorium be placed upon the use of such materials until such time as a suitable program structure for their use can be demonstrated. It should be noted that this moratorium will serve a useful incidental purpose in allowing the populations of natural biological control agents to recover from the effects of previous pesticide use. The Committee recommends that for the coming year that non-pesticide "baseline" nuisance abatement techniques be pursued. using Town resources. A part of this effort would be research to determine if effective use can be made of preferred larviciding materials ( Category B) . The following program elements are suitable for inclusion in the recorrended program: a) Public education efforts should increase awareness of the need to eliminate mosquito breeding sites existing on private property. Several troublesome mosquito species seldom travel more than a few hundred feet from the larval habitat, so the nearer the breeding site to residences, the greater the nuisance potential. Clogged gutters provide highly adequate breeding sites. Flower pots which collect water and bird baths are also likely to be used. Unused swimming pools or ornamental ponds can create significant local problems if they are neglected.. b) The public should be made aware of the need to keep brooks and drainage channels free of trash, leaves, and grass clippings. Such debris not only creates pools of stagnant water, but provides organic material which mosquito larvae feed upon. A Town bylaw is available to enforce this item, but social pressure alone would probably be adequate if the connection between such dumping and mosquito breeding became common knowledge- 13 c) Water flow in brooks should be checked, improved, and protected. The Massachusetts training manual for commercial pesticide applicators states that "many streams in Massachusetts are burdened with erosion products (silt, mud, etc.) or log jams that have resulted from past land use patterns that were destructive. Cleaning these materials from streams restores them to a condition closer to their original status and. . . reduces mosquito breeding." The Town should remove obstructions which interfere with the flow of brooks. The Lexington Conservation Commission should exercise great care to make sure measures are taken to prevent siltation during construction activities. d) Every effort should be made to maintain and improve water quality in brooks and wetlands. The training manual for commercial pesticide applicators notes that most mosquito larvae are "indiscriminate and omnivorous and will feed on all kinds of minute organisms. These food organisms flourish in water polluted with garbage and human and animal wastes. Such polluted water will support amazingly large populations of certain mos— quitoes compared to equal amounts of clean water. Cleaning up water can reduce a big mosquito problem to a small one. Also clean water will support the predators of mosquito larvae". e) The public should be made aware of the effectiveness of mosquito repellents, suitable clothing, proper toiletry, and screening in providing protection against mosquitoes which are present in the environment. Personal protection is more effective than any government program in reducing the number of mosquito bites which are suffered in outdoor activities. 14 f) A survey should be made of mosquito natural enemies and competitors which occur or should occur in Lexington. Their habitat requirements should be determined and habitat manipulation considered as a means of increasing their numbers. Certain areas of Lexington, such as Tophet Swamp, 'have no swallows due to an apparent lack of nesting sites. Local conservation groups should be asked to assist in the erection of nesting boxes in the area. In areas where fish kills have occurred, fish should be restocked and their populations checked periodically g) Existing drainage channels and ditches in wet areas where mosquitoes. might breed should be mapped and maintained. New drainage or ditching should be attempted only as part of an overall pest control program and only under a letter of agreement with the Lexington Conservation Commission. h) Breeding containers (such as old tires or bottles.) along roaasides and on public land should be removed by Town work crews con a regular basis. i) If sufficient funds are available, a summer employee should be sought to investigate mosquito nuisance problems in. LexAngton and to coordinate Town resources in resolving particular problems. This employee should be capable of surveying areas where mosquito nuisance exists, mapping mosquito breeding areas, and identifying the particular species of mosquitoes causing problems (Since different species breed in slightly different habitats and travel different distances, such 4ata provides important clues concerning how problems might be. resolved). 15 + 4.0 Recommendations for the Future 4. 1 Future Use of Chemical Pesticides The baseline nuisance abatement techniques exert a constant suppresive force upon the mosquito population in contrast to pesticides, which have only temporary effect. Hence baseline techniques provide the foundation for a control program and pesticides must be integrated carefully into the overall effort. The following five issues should be addressed in planning future use of pesticides: 1) Need. Do problems remain which the program does not, now resolve? Exactly what is the nature of the problem and what level of control is required to resolve it? 2) Alternatives. What are the alternatives for resolving the problem? Are non-chemical approaches applicable? Have they been tried? 3) Effectiveness. Exactly what level of net reduction in mosquito nuisance is expected from the pesticide use being considered? 4) Compatibility. Is the pesticide use compatible. with the other. control efforts? Does the pesticide use complement or replace natural controls? 5) Safeguards. Do sufficient program safeguards exist to reduce risks of human exposure to acceptable levels? Do sufficient safeguards exist to ensure that no significant ecological damage will result? 4.2 Future Membership in the East Middlesex Mosquito. Control Project In theory at least, membership in a regional mosquito control project can offer certain advantages - It allows more than one town to share personnel and expensive equipment. - It allows control efforts to be carried out by personnel with more specialized experience in pesticide application and mosquito control. 16 - It encourages cooperation in control efforts among towns which share common borders. Certain disadvantages may also result: - The seasonal nature of mosquito control may result in the full-time work force having little to do at certain times of the year and being, overloaded during the summer. - Mosquito control may become a single-minded pursuit in which conflicting interests and concerns are not properly considered. - Programsmust be planned on an area-wide basis and often cannot be tailored to a particular town's needs or wishes. - Since responsibility is transferred to an outsideagency, private citizens and Town governments are inclined to neglect their own responsibilities in dealing with mosquito nuisance problems. The management objective of the E.R1CP program appears to be to provide as much impact upon mosquito numbers as possible given a very small. (often totally inadequate) amount of funding. During the summer, this objective is viewed in terms of applying as much pesticide as possible given the available resources. Monitoring of pesticides, safety precautions beyond those legally required, coordination of town resources, and public education efforts are viewed as diversions of scarce resources from the top priority. Hence EMMCP is primarily valuable as an agency for applying pesticides, but is not well suited for providing the other program elements identified in this report. If Lexington chooses to pursue a no-pesticide or nthdhut -pesticide program, then a role for EMMCP becomes somewhat-difficult to define. Reconsideration of EMMCP membership might, however, be desirable if EMMCP were to offer a formal program option in which planning and monitoring activities were more suitable for the type of materials to be employed. This would probably be contingent upon the willingness of other towns in the E1T'CP service area to share in the funding of improved EMMCP capabilities in program planning, pesticide monitoring, and the use of non-toxic control techniques. Any decision 17 to transfer program responsibilities to an outside agency should be made only after full specifics have been worked out and made available for review by both Town boards and the public. These ideas will be more fully developed in the final report of the Pest Control Advisory Committee. 18 APPENDIX A The Decision-maLing Process. Mosquito Control and Controversy The following paragraphs are taken from the"Training Manual for Commercial Pesticide Applicator Certification in Massachusetts in Cat. 8 : Public Health". The title of the section is "Mosquito Control and Controversy" " Nothing is free. Every gain is coupled with a loss in some sort of trade off. Whether a given trade off is seen as good or bad depends on how priorities and values are assigned to the things gained and the things lost. Only if the gains are major, the losses small or seen-as-small, and the values of the community relatively uniform-only then will an action. be viewed not as a trade off, but as pure gain. Specifically, with respect to mosquito control, the gains are disease control through vector reduction and nuisance abatement (less biting) . In the northeastern U.S . only en- cephalitis and heartworm are diseases prevalent enough to be considered with respect to mosquito control policy . Even they are minor, or rare problems Certainly no disease-control justification exists in MASS comparable to tropical areas where malaria and other mosquito-borne ,;diseases have the potential to devastate the human population. The value of nuisance abatement must be considered for three different types of areas built-up residential zones, outdoor recreation areas that receive heavy use (such as beaches and perhaps park campgrounds) , and the general outdoors environ- ment . Nuisance abatement in heavily used recreational areas has economic importance through its effect on tourism in that people would be less likely to seek out mosquito-infested areas to vacation . Nuisance abatement in residential areas and the general outdoors environment has less economic importance and more importance in regard to comfort of local residents.. Nui- sance abatement for the general outdoor environment has the least importance of these three 19 The losses from mosquito control vary in intensity depend- ing on the methods used, the chemical employed and the intensity of control attempted But some losses occur with all control programs (i e nothing is free) Some of the losses (or costs) are 1 The cost of the cortrol program itself. 2. Impacts on living creatures , such as a) Death of related aquatic insects and crustaceans in control areas , and perhaps eggs and/or fry of fish b) Interference with biological control agents on ornamentals in regularly-fogged suburban environ- ments 3 The potential for unwanted surprises from chemicals irtroduced into the environment (Our knowledge is always incomplete Although our ability to prejudge and evaluate the potentially troublesome attributes of the chemicals we use, is improving, it would be presumptious to assume the future will not reveal to us areas in which we are today ignorant .) With these potential gains and losses in mind, different people evaluate mosquito control practices and come up with different conclusions This is due to two reasons: 1 Each has a slightly , or perhaps greatly, different set of information and experience available to him to judge with 2. Different people set different values on the gains and losses . The decision to attempt to control or not to control mos- quitoes in a given area is essentially a political decision. " 20 4 APPENDIX B BIOLOGY OF MOSQUITOES Certain facts concerning the biology of mosquitoes are important in understanding the reasons for their prevalence in New England and the relative effectiveness of various mosquito control measures. Mosquitoes are members of the insect order Diptera which includes flies and midges. Only adult female mosquitoes "bite" (actually they suck, but it would not occur to most people to complain of being sucked by mosquitoes). The nourishment provided by the blood meal is used by the female mosquito in the production of eggs. There are over 40 species of mosquitoes in Massachusetts. Some species bite only amphibians or only birds. Only about half a dozen species are significant pests for human beings in our area. Mosquitoes have four stages in their life cycle: egg, larva, pupa, and adult. Larvae are aquatic and require stagnant water in which to develop. They feed almost exclusively upon small particles of organic matter floating in water. The time. required for development from egg to adult averages about 10 days - but can be as short as five days. Water with high organic content supports more larvae and allows them to develop in a shorter span of time. Different species have different larval habitat preferences. Some breed. mostly in small containers and temporary pools. Others will breed in permanent water. One group of pest mosquitoes, known as the reflood group, lay eggs just above the water line, of quiet pools. When rainfall causes water levels to rise, the eggs are covered and soon hatch. Other species lay eggs directly in the water. Some species have only a single breed in early spring - others breed continuously during the warmer months of the year. Mosquito larvae have no gills - they must swim to the surface of the water to obtain air. For this reason, a larvicidal oil which creates a temporary thin film on the water surface will kill mosquito larvae. 21 Some nuisance species do not travel more than a few hundred feet from the larval habitat. Others will disperse several miles from the breeding site. Life spans of adults range from a few days to two or three weeks. Dehydration (loss of body moisture) is a problem for adult mosquitoes. For this reason they shun dry sunny areas and are most active in subdued light. Among the natural enemies of mosquito larvae are dragonfly nymphs, parasitic nematode worms, and small fish. Nematode worms and fish (especially Gambusia , the "Mosquito Fish") have been successfully used as biological control agents. Among the natural enemies of adult mosquitoes are frogs, spiders, insectivorous birds (especially swallows), the praying mantis, and bats 22 APPENDIX C MOSQUITOES AND PUBLIC HEALTH • The training manual for public health pesticide applicators in Massachusetts (Reference 1) states that "in the northeastern U.S. only encephalitis and heartworm are diseases prevalent enough to be considered with respect to mosquito control policy. Even they are minor, or rare problems. Certainly no disease-control justification exists in Massachusetts comparable to tropical areas where malaria and other mosquito-borne diseases have the potential to devastate the human population." The transmission of human disease by mosquitoes is not a significant concern with respect to mosquito control in Lexington. Equine encephalitus, the only mosquito-borne disease of significance in New England, has never been reported in Lexington. In Massachusetts it is confined primarily to. Bristol and Plymouth Counties where the topography is more suitable for the known carrier of EEE, the mosquito species Culiseta melanura. State agencies monitor the presence and prevalence of equine encephalitus and implement control measures if they are needed. Nuisance abatement programs such as those carried out in previous years in Lexington are inadequate for disease control and fail to meet basic standards of medical entomology.. Although not a concern for human health, heartworm is a debilitating and potentially fatal disease in dogs. It is transmitted from one infected dog to another by several species of mosquitoes. The occurrence of heartworm in Massachusetts is apparently rising although it is relatively unusual in Lexington. Medication is available which provides essentially complete protection against transmission. One local veterinarian. has estimated that approximately 60% of Lexington dog owners now give their pets such medication as a matter of course. Board of Public Health rabies clinics provide literature to dog owners which recommends medication. Unmedicated pets are not only potential victims of the disease, but are potential carriers capable of infecting other unmedicated dogs Mosquito control programs such as have 23 been carried out in the past would appear to have contributed littleto the enhancement of canine health in Lexington. The effective barrier to transmission resulting from medication appears to be the most effect means of suppressing heartworm. A recent survey of Lexington physicians (March 1980) provided information upon the relationship of mosquitoes to human health in Lexington. Responses were received from 22 of 29 physicians polled. The responses revealed the following 1) None had seen any serious illness due to mosquito bites in Lexington in experiences ranging from 5 to 46 years of practice. 2) Half had seen cases of infected mosquito bites (due to scratching). These occurred in the range of 2 to 8 cases per summer. 3) A few reported cases of allergy to bites (extreme local reaction). 4) 17 (77%) felt that mosquitoes did not represent a significant medical problem in Lexington 5) Fourteen of the 22 (64%) considered mosquitoes to be enough of a nuisance to justify some type of nuisance abatement effort. Although admittedly, the rhvc;rians were not especially knowledgeable concerning mosquito control techniques, they were asked what type of mosquito nuisance abatement measures they would favor. The results were general spraying of adulticides. 2 (9%) very limited use of adulticides 7 (32%) larvicides 6 (27%) ditching and draining 10 (45%) Eight physicians (36%) were definitely opposed to any pesticide use in the abatement program. 7) No reports were received of toxic injuries associatedwith past use of pesticides in Town programs. 24 6 APPENDIX D RISKS INVOLVED IN HUMAN PESTICIDE EXPOSURE The evaluation of potential risks from human pesticide exposure. is not a straightforward task. Some of the most obvious and basic questions concerning the effect of pesticide exposure upon human beings have never been answered.1 One reason for this is that experimentation with human subjects is difficult to organize and is constrained by ethical considerations. Another is that answering some questions requires greater knowledge of biochemistry and toxicology than now exists. There are a wide variety of toxic effects upon human health which could potentially result from exposure to pesticides. Many of these effects are quite independent of the particular toxic mechanism which gives the pesticide its economic value against the pest species. Complete testing of all possible avenues of injury would be economically infeasible, even if the scientific basis for such testing existed. The process of evaluating pesticide risk involves taking available information into account and developing an appropriate respect for the potential pitfalls resulting from incomplete knowledge. Organophosphate Insecticides The organophosphate insecticides used in mosquito control adulticiding -(malathion and Dibrom) function by interference with the nervous system. Their principal means of action is through inhibition ofan enzyme known as cholinesterase which is critical to the proper transmission of nervous impulses from one cell to another. This substance is common to both man and insect. Mammals are somewhat tolerant of organophosphates such as malathion since their blood contains certain enzymes which attack and detoxify the malathion which enters the body. Insects, lacking such enzymes, receive the full force of the malathion poisoning action. In. mosquito control operations the insecticide is applied at concentrations which kill insects but are many times less than the concentrations at which symptoms 1 For instance, a pregnant woman asks if her exposure. to an insecticide which acts through attack upon the nervous system could have any effect upon the rapidly growing nervous system of her unborn child. She is almost certain to find that no one has ever investigated the question. 25 of organophosphate poisoning normally appear in human beings. Thus insects should be controlled without poisoning human beings. Individual Variation. The above picture is somewhat complicated by the fact that individuals vary widely in their ability to resist the organophos- phate action. The elderly, infants, and chronically-ill persons are known to be more susceptible to exposure. Malathion is also known to create synergistic effects when individuals are simultaneously exposed toother compounds (including other pesticides) which are themselves not expecially toxic, but which interfere with the ability of the body to detoxify malathion. Organophosphates are also believed to modify the actions of psychotropic medications (Reference 4 ) . Hence there may be a small number of individuals in a community who are unusually susceptible to injury from the pesticide Safe exposure levels can be defined in terms of averages, but it is essentially impossible to find a scientific basis for guaranteeing safety for area-wide applications in a community of varied individuals. Other nervous system effects. Exposure to organophosphates is known to produce abnormal electroencephalograph readings for months after any signs of cholinesterase inhibition have disappeared.(References 5 and 6 ) These abnormal readings may be accompanied by complaints of insomnia,. anxiety, sexual problems, etc. One pair of medical researchers reported an increased incidence ofRppsych tic aberrations in workers exposed to organo- phosphate insecticides.,,?Xbrkers in an insecticide factory in Texas began. to exhibit symptoms which were initially ascribed to multiple sclerosis. Further investigation revealed that the organophosphate insecticide being produced possessed "delayed neurotoxic" action which led to disintegration of axons in the nervous system. (Reference 8 ). Low doses of organophosphate pesticides have been found to produce changes in the central nervous system which interfere with visual performance.. This discovery was made by aviation medicine researchers who were concerned that pilots involved in aerial pesticide applications might suffer effects which endangered flight safety. One report warns that: 26 0 " the effects may be subtle and not immediately apparent to the exposed person, his co-workers, or his physician. . . no sense of dysfunction need be present. Nevertheless, under some cond- itions, reflex responses to visual signals will be inappropriate and a crash can be the result." (Reference 9 ) " OP's (organophosphates) , atropine, and other drugs affecting cholinergic functions can be hazardous to aerial applicator per- sonnel and other exposed persons, even at doses too small to have grossly detectable sequelae." (Reference 10 ) These effects are not of obvious concern for the average person, but may be of concern for persons performing tasks requiring high levels of visual coordination. Exposure level. The primary means of exposure to individuals during mosquito adulticiding operations is probably through direct inhalation of the aerosol. Ingestion through eating sprayed food articles and absorption of insecticide through the skin are other routes of exposure. Double exposure is likely if location is near the intersection of two treated streets. Some feel for concentrations in air is given in Figure D.1. It can be surmised that exposure resulting from mosquito control would be at levels which would have some effect upon body chemistry, but which would be well below exposure levels of industrial workers. Because the level of exposure is low, the likelihood of injury is decreased. Variations in individual susceptibility and the possibility of subtle5as-yet-undetected effects must, however, be acknowledged. 2.7 FIGURE D. 1. Data on concentrations of malathion in air. 10. — 1. 4— Measured worker exposure (high) 4.b •ri . 1 <--Threshold Limit Value (industrial, standard) EH—Cholinesterase fluctuations in humans after repeated exposures .0 1 - Z 0 1:4 4—IApproximatemosquito adulticiding concentrationf r.4 oz .001 — C-) < Effects on conditioned reflexes of cats r--: <--- USSR Industrial hygiene standard .0001 — < Found in air sample in Florida community .00001 -- 28 Conclusions Pesticide use in mosquito control seems to conform to current safety standards for industrial, agricultural, and public health operations. These standards provide some protection against known adverse effects. Concern over safety persists in the area of subtle, rare, or as—yet-undocumented injury. Scientific knowledge is incomplete in many significant areas. Since the effects of exposure depend upon individual susceptibility, the probability of injury increases with the number of persons exposed. It also increases with the frequency of exposure, thedosage, and the number of different pesticides used. The desire of some persons not to be exposed to pesticidesappears to be a legitimate request In pesticide applications, the principle of informed consent should be applied insofar as possible. Currently the material to be used in mosquito control project work is sometimes determined by price or availability. Butwhenever human exposure is possible, safety considerations should be given priority. A mosquito control program should utilize an integrated control approach which minimizes or eliminates human exposure to chemical pesticides whenever possible. Suitable monitoring and health protection measures shouldaccompany any introduction of pesticides into the environment. If such measures cannot be implemented for some reason, serious consideration should be given to methods of avoiding pesticide use. 29 APPENDIX E PESTICIDE USE PLANNING AND MONITORING There are several measures which are advisable to enhance safety and effectiveness of pesticide use in suburban environments. Such measures are often omitted by pesticide applicators due to a lack of trained personnel, lack of funding, or lack of concern for inadvertent effects. Lack of safeguards sometimes leads to significant levels of pesticide contamination, pesticide overuse, or environmental damage before affected persons become aware of the problems. The following list suggests measures which are advisable in a program which introduces chemical pesticides over a significant area. a) There should be periodic testing for pesticide residues in air, water, and soil. This testing should look for degradation products as well as the original compound since such products are often toxic and stable, hence subject to accumulation. Because pesticide residues may be flushed out of wetlands and enter flowing water, testing downstream of the tea of application is advisable. b) There should be special periodic medical examinations and medical h story follow-up for personnel involved in the application of pesticides. This is not just "their problem" since effects detected in workers often provide the early warning signs that effects may be occurring in the general population c) In the case of aerosol applications, there should be some type of medical monitoring of the community for pesticide-related effects. This might involve establishment of contact with local physicians or checking unexplained absences from school after spraying operations. Because in many cases pesticide effects upon the nervous system are not recognized as such, even by physicians, lack of a reporting/alerting system can readily result in such effects being ascribed to other causes. 30 + W 4 d) Areas where spraying of insecticides is to be allowed should be designated with public participation and with full knowledge of Town boards. It is impossible for a mosquito control project or a single Town board to to be aware of all the legitimate interests which may be affected by spraying a particular area. The procedure to be used is thus to declare the whole Town "no spray" and then proceed, with full public participation, to designate exceptions. e) There should be an effective means for respecting "no spray" areas. The current procedure which requires telephone request fromthe affected parties and cut-off of the aerosol generator at the property line does not prevent exposure. House lots in Lexington are small and aerosols, even in the absence of wind, drift over 300 feet. f) Special consideration should be given to preventing pesticide exposures resulting from recreational activities in areas treated with larvicidal materials. One concern is exposure of winter recreationists in areas treated with "pre-hatch" dusts. Another is the possibility that materials placed in wetlands will be flushed into recreational waters. g) Before pesticides are introduced into an area there should be a biological survey to quantify the fauna of the site. Special attention should be given to any natural enemies of mosquitoes which may be present.. Competitors of mosquitoes (such as non-biting midges) which may slow mosquito production in certain locations should be identified. The control program should be tailored to complement, not destroy, any natural controls which are present. Non-target populations should be checked periodically if pesticides are used.. The net impact of the pesticide use upon the mosquito population of the site should be estimated taking all relevant ecological effects into account. h) There should be a periodic detailed professional review of the control program by persons without direct connections with the program. At these reviews the question of the balance between pesticide use and other control techniques should be considered. The adequacy of planning, monitoring, and coordination should be considered. The Town should also be given an objective evaluation of the level of benefits which they are receiving for their expenditure. 31 1 APPENDIX F EAST MIDDLESEX MOSQUITO CONTROL PROJECT Background For the past 35 years mosquito control work in Lexington has been planned and executed by the East Middlesex Mosquito Control Project (EMMCP). Based in Waltham, the EMMCP is a public trust operating under the State Reclamation Board. Their funding comes not from the state, but from the 15 cities and towns which they serve. Currently they are active in the towns of Arlington, Belmont, Brookline, Burlington, Cambridge, Framingham, Maynard, Newton, Sudbury, Waltham, Watertown, Wayland, Wellesley and Weston. Mosquito control activities in Lexington terminated on June 30, 1979 and Lexington is considered to have formally withdrawn from the Project. The work force of the Project consists of 4 permanent field men, 2 foremen, and 2 laborers. Additional part time personnel may also be used. The EMMCP is governed by a 15 person commission which is composed of one representative from each town served. Budget Some idea of the budget of the E!MCP can be obtained from the following breakdown of 1979 expenditures charged to Lexington: Labor (water management and spraying) $2093.81 Insecticide 477.29 Insurance 549.85 Retirement 207.85 Utilities 163.80 Rent 181.24 Office & Adm. 814.85 Shop & Supv 250.36 Fd. Eq. & Oper. 614.97 Other Services 66.63 Ratio Adj . 3.86 Total $ 5424.51 32 Control Techniques There are basically five control techniques employed by EMMCP. They are pre-hatch larviciding, summer larviciding, adulticiding, water management, and catch basin treatment. The project will carry out activities in all or some of these areas, subject to manpower limitations. Pre-hatch larviciding. Methoxychlor dust is applied to frozen swamps in late winter as a treatment for the spring brood of Aedes mosquitoes. Application is at the rate of 1 pound of active ingredient per acre. The dust may blow around somewhat before becoming stable on the surface of the ice or snow. The effectiveness of the larvicide may persist for several weeks in early spring while the water is cold.. It seldom has any effect after the end of May. Cost of this treatment is modest (about $3 per acre treated) . In a typical year about 200 acres in Lexington. =ere treated in this manner. Summer larviciding. The principal insecticide used for summer larviciding is Abate (temephos) , an organophosphate Summer larviciding is directed mostly toward mosquitoes which appear following summer rains. Visual inspection of sites to verify the presence of temporary pools of water and mosquito larvae are used to direct the effort Abate has very little residual effect (only a couple of days) and hence interrupts only one brood of mosquitoes. Summer larviciding is fairly expensive (about $70.00 per acre) . In 1979 about 4 acres were treated in this manner in Lexington during April and May. Adulticiding Adulticiding operations utilize truck-mounted ultra-low volume aerosol dispensers The insecticides used are either Cythion (malathion) or Dibrom (naled) . Both of these materials are organophosphates. In 1978 about 29.5 gallons of L'LV spray were applied - enough to cover about 2700 acres once. In the spring of 1979, 22 gallons were applied. Typically, spraying takes place 7 or 8 times during the year with a few hundred acres being treated on each visit. See Appendix H for further discussion of adulticiding techniques and effectiveness. Water Management. Water management work is done with picks, shovels, and other hand tools. The objective is to drain pools in which mosquitoes breed. In 1979 about 1500 feet of drainage channels (more than normal) were cleared or re-dug in Lexington. 33 4 Catch Basin Treatment. Methoxychlor or Baytex are sprayed into catch basins to kill both adult and larval mosquitoes. Pesticide Selection. Pesticides, to be used are selected on the basis of effectiveness, safety, price, and availability from the supplier. An additional reason for changing pesticides occasionally is to decrease the likelihood of pesticide resistance among the mosquito population (no resistance has been observed to date) . Other Program Elements EM4CP conducts no public education program. There is no organized effort to enlist the aid of town resources in reducing the level of mosquito nuisance. No effort is directed toward enhancement of populations of natural enemies of mosquitoes. Pesticide Monitoring EMICP does not attempt to monitor the effects of pesticides upon non-target organisms. No biological survey is carried out prior to introducing pesticides into an area. There is no testing for pesticide residues in air, water, or soil. There is no active effort made to contact. physicians, nursing homes, or hospitals concerning possible health effcts of pesticide spraying. There are no medical exams aimed at detecting possible pesticide effects among workers handling pesticides. Precautions Associated with Pesticide Use Pesticides are applied in accordance with the label approved by the Federal Government and subject to any additional restrictions imposed by the state. Employees are provided with gloves to be worn during the work, although some employees choose tot to wear them. There is no testing. of tha particular batch of pesticide being applied except for the tests which may be done at the factory before shipping There is no procedure for general warning of the public concerning areas to be treated or times of treatment. 34 Individuals who so request may be notified by telephone of spraying operations. Such requests may come from persons with respiratory problems or from. pregnant women. "No spray" requests are honored by turning off the aerosol generator at the property line. Research and Experimentation Although no money is explicitly set aside for research, some experimentation with different pesticides is carried out, especially when the manufacturer provides free products for testing. The experiment generally consists of applying a material to a small test plot and observing the effects upon the mosquitoes present. A recent experiment with a larvicide consisting of a strain of Bacillus thuringiensis supplied by Abbot Labs was highly successful. 35 APPENDIX G EFFECTIVENESS OF ORGANIZED MOSQUITO CONTROL EFFORTS Previous mosquito control efforts in Lexington have failed to prevent considerable numbers of mosquitoes from persisting in the environment. Similar observations have been made in other towns. A review of Lexington's past program has indicated that several factors have limited and will continue to limit the results to be obtained: a) Only a small fraction of the existing mosquito breeding sites have been treated with larvicidal materials. Less than 200 acres have been subjected to pre-hatch dusting and .only a fraction of this acreage to summer larviciding. Effort has been concentrated in a few of the larger wetland areas. Many smaller areas near residences have been missed. b) Only limited areas have been treated with truck-mounted aerosol dispensers. The effect of the aerosol extends less than 300 feet from the street. Mosquitoes from untreated areas are able to infiltrate. into the treated areas (see discussion of adulticiding in separate section) . Typically, the amount of insecticide used in ULV applications in a year is sufficient to cover only about 2700 acres (the area of Lexington is 10,650 acres) . In practice, 7 or 8 visits to the Town are made and a few hundred acres are treated on each visit. c) The insecticides used largely lack. residual action. Adulticiding materials in particular are lethal to mosquitoes for only a few hours after application. Although pre-hatch larvicides can be more persistent (sometimes halting mosquito breeding for several weeks in May) , summer larvicides are lethal for only one or two days. Note: more persistent materials are generally not usable due to problems of accumulation, contamination, and biological concentration in food chains.. d) The frequency with which materials have been applied has often allowed mosquito populations to recover between applications. e) Because the materials used are toxic to natural enemies of mosquitoes, they may sometimes remove natural checks upon mosquito densities. This allows mosquitoes to recover, after the effect of the insecticide disappears, to a level higher than would otherwise have existed. Hence widely spaced applications of insecticide can actually result in a higher average level of mosquitoes than would exist without insecticide use. 36 P • f) Ditching and drainage to eliminate breeding pools is a permanent and highly effective solution for some breeding sites. However the draining of many breeding locations is impossible without the use of heavy machinery and/or destruction of wetland values. It may also be very expensive. Since mosquito control projects are exempt from compliance with the Massachusetts Wetlands Protection Act, special local control mechanisms would be advisable before approving such operations. g) No significant source elimination effort has been directed toward breeding sites located on private property. The proximity of these sites to residences makes them of genuine concern in terms of nuisance reduction. Often residents inadvertently create breeding opportunities for mosquitoes by providing water containers, dumping trash in drainage channels, etc. A possible response to the pesticide effectiveness problems discussed above would be to increase the frequency of pesticide applications and to attempt to cover a much larger area. But it should be understood that such escalation could be very expensive1 and ultimately frustrating. It could largely destroy the natural biological checks upon the mosquito population. It would inflict greater damage upon beneficial and innocuous non—target species. The risk of injury to human health due to pesticide exposure would be substantially increased. Such actions would also increase the likelihood that mosquitoes would evolve resistance to the pesticides being used. Resistance would require heavier pesticide use or switching to more expensive or hazardous products 1 A single larvicidal application during the summer costs approximately $70 per acre treated. Repeated treatments are necessary for continued effect. 37 APPENDIX H ANALYSIS OF MOSQUITO ADULTICIDING OPERATIONS In recent years the East Middlesex Mosquito Control. Project has. conducted periodic mosquito adulticiding operations in Lexington using ultra-low volume (ULV) aerosol generators mounted on trucks. The insect- icides employed have been malathion (Cythion) and naled (Dibrom). These are broad-spectrum organophosphate materials. They have little or no residual effect since mosquitoes must be struck by the aerosol to be killed and are not controlled after the aerosol has settled. Larvae and pupae in the vicinity are not controlled by the application. The area to be treated is determined by nuisance complaints and by knowledge of where adulticiding was required in. previous years. In some cases a landing count is taken prior to spraying. This involves counting (and collecting) the number of mosquitoes which land upon a person's exposed arm in a ten minute period. In the absence of wind the effect of the application extends to about 300 feet on either side. of the street. Since the aerosol will drift with the wind, a cross breeze makes it impossible to cover one side of the street unless it can be covered from a nearby parallel street located upwind. In some cases the effectiveness of the operation is determined by taking a second landing count one or two days after the spraying. The effectiveness thus determined varies from about 35% to 95% with an average of approximately 66%. Effectiveness varies with the season (less effective early in season) , location with respect to cross streets (double coverage occurs near intersections) , and time of application (most effective at dusk and near dawn). The mosquito population begins to recover soon after the application. Recovery can occur in two ways. First, adult mosquitoes from. outside the sprayed area can infiltrate as soon as the aerosol has settled. They supplement the mosquitoes within the sprayed area which survived the application. Secondly, continued emergence of mosquitoes from breeding sites in the area provides new recruits into the pest population. 38 4 Recovery Time The time required for the mosquito population to recover to normal levels following a pesticide application is an important consideration in the eval- uation of adulticiding effectiveness. The effectiveness numbers quoted in mosquito control project reports reflect the drop in mosquito numbers which follow immediately after the application Since these numbers represent only a temporary condition, they can be misleading when applied to the evaluation of the effectiveness of the application over an entire. season. A more appropriate measure would be the average decrease in the mosquito population when averaged over the mosquito season (or over one spray/recovery cycle) . In order to obtain some insight into the recovery time, a plot of 1979 landing count data collected by East 'fiddlesex Mosquito Control Project was constructed (see Figure H. 1) Each data point corresponds to a separate before/after landing count check of adulticiding applications at various locations within the ENNCP service area (only two of the checks were made in Lexington) From this data it appears that the mosquito population substantially recovers by about the third day after the application. Unless applications take place approximately every three days, the average effectiveness of the operations may be mLch less than the "knock-down' effectiveness. Need for Control Areas In a complaint-directed spraying program, applications tend to be made when mosquito populations are at a peak in the target area. At such times there is a statistical tendency for populations to decline toward normal levels This can result in data showing apparent long-term effects of the application when, in reality, declines in the mosquito population took place due to natural factors independent of the pesticide. The standard method of resolving this question is to establish control plots which are 39 not sprayed. If the mosquito population declines on the unsprayed plots in a manner comparable to the decline on the sprayed plots, then the decline is not credited to the pesticide use. Benefits are defined in terms of the differences between the treated and untreated areas. The use of control plots is not standard practice in mosquito control project operations, hence the impact of natural fluctuations in mosquito numbers is difficult. to determine. 1.0 I I I I oo 0.9 — — 0.8 — a 0.•7- — • El 40 • 0.6 — • 9. 0.5 — — 0.4 • c 0.3 ! H 0 2 -- ® ® — o • 01 — — • 0.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 DAYS AFTER SPRAYING FIGURE H. 1 Mosquito landing count expressed as a fraction. of the pre-spray landing count for 1979 ULV adulticiding operations by the East Middlesex Mosquito Control Project (Reference 12). 40 t Adulticiding Coverage in Lexington In order to evaluate the impact of adulticiding in Lexington upon mosquito numbers some simple mathematical realtionships between insecticide use arid coverage were worked out (see Table H.1) . It can be. seen that each gallon of ULV insecticide covers approximately 90 acres or approxfirately 1.8 street miles. The following data on EMMCP activities is available: - In 1978, 29.5 gallons of ULV insecticide was applied. - In 1979, 22 gallons of ULV insecticide was applied (before June 30) . - Typically, EMMCP trucks were in Lexington 7 or 8 times per year.. If use of 30 gallons is considered typical, then: - By area, 30 gallons ULV covers approximately 2700 acres. The area of Lexington is 10,650 acres. - By street miles, 30 gallons ULV covers approximately 53 miles.. 'There are approximately 130 miles of street in Lexington. - EMMCP trucks visited Lexington on an average of about once every 17 days during the mosquito season. - Only a few hundred acres were sprayed on each visit. From the above data it can be seen that most areas of Town. did not receive even a single treatment. The time between treatment for any given area is on the order of weeks. This spacing appears to be much greater than the recovery time. Counterproductive Effects If pesticide applications destroy natural biological controls (see Appendix I) then the mosquito population may rebuild after the application to a level higher than would have existed without the application. In order to prevent this, the pesticide must be re-applied in a period which is comparable with the recovery time. In Lexington the re-application period appears to have been much greater than the recovery time. Hence if there is any interference with natural controls, there may be significant intervals 41 ; 1) TABLE H.1 ADULTICIU)1, G COVERAGE RELATIONSHIPS STML DEFINITION NOMINAL VALUE V Speed of truck while spraying 7 mph w Lateral distance to which spray is effective 300 feet c Efficiency of routing. Equals time spent spraying 0.70 divided by total time in area. Allows for dead-end streets, back-tracking, etc. ; k Overlap factor. Equals area covered divided 0.70 by area which would have been covered in absence of any overlap. p Basic rate of application (fluid oz./acre) assuming 1.0 fl. oz./acrei no overlap. p' Average rate of application allowing for overlap. 1.4 fl. oz /acrei Q Quantity of insecticide applied. A Area covered by the application S Street miles covered by the application Time devoted to the application -a a Area subjected to double coverage due to overlap. 14 RELATIONSHIPS A = 2 w V c k TN Nominally, A = (249.5 acres/hr) Ta S = V c Ta Nominally, S = (4.9 mi/hr) Ta. p' = p/k Nominally, p' = 1.4 p If triple overlap is ignored k = A/(A+a) or a = A (1-k)/k Nominally, a = 0.43 A where 0.5 -‹ k 5. 1.0 A = Qk / p Nominall A = (89.6 acres) 0. gal S = Q / (2 w p) Nominally, S = (1.76 mi ) Q gal 42 ft of time in which the mosquito population is worse than it would have been without pesticide use. Because the pesticide application may be trading natural controls which work constantly against pesticide control which works briefly, it is important to average the effect over the spray/recovery period in order to fairly evaluate benefits. When this is done a modest but. constant reduction by natural controls may well prove more beneficial than a dramatic but brief reduction produced by pesticide applications. Due to the lack of control plot comparisons and lack of monitoring of non-target species it is not now possible to judge the level of control being provided by biological agents or the extent to which pesticide use has interfered with such control. Conclusions Adulticiding in Lexington has been restricted to a small fraction of the To from which complaints have been most persistent. The pesticide application usually results in a drop in the number of mosquitoes to less than one-third the pre-spray numbers. The mosquito population substantially recovers in one to three days. The time period between spraying operations is several weeks. If the spraying injures natural control agents this may result in several weeks in which the mosquito population is higher than it would have been without pesticide use. A better understanding of natural control is required to fully evaluate the benefits (or damages) of adulticiding. 43 [APPENDIX I EFFECTS OF PESTICIDES ON NON-TARGET ORGANISMS The pesticides most cOmmonly used in mosquito control. efforts are "broad-spectrum" materials which affect a wide range of organisms. In terms of marketing strategy, this is a desirable property since it means that the same material can be sold to control a variety of pests. However it also means that unintentional ecological impact can result more. easily. Reasons for Monitoring Non-target Organisms Pesticide effects on non-target organisms should be considered in planning a mosquito control program. The following, reasons are relevant: 1) Pesticides can injure the natural enemies of mosquitoes and. hence result in increased production of mosquitoes after the pesticide effect wears off. In general, mosquito predators require much longer than mos- quitoes to complete their life cycle and hence recover much more slowly than the pests, 2) If pesticides are more destructive to competitors of the nuisance species (such as non-biting midges or mosquito species which bite only amphibians) than to the pests, then they may alter the competitive balance of nature in an undesirable way. 3) Fish and wildlife are a valuable resourcefor educational, aesthetic, and recreational reasons. Town and state funds are spent to preserve wildlife populations and habitat. Mosquito control should not needlessly destroy these resources. 4) Secondary pest outbreaks (of mites, scale insects, etc.) can occur if mosquito adulticiding destroys beneficial predatory insects. Without monitoring, the connection between such outbreaks and the mosquito control applications may go unnoticed. Ideally, a survey of the natural populations of organisms would be conducted prior to pesticide use in an area. Unfortunately, this was not done in Lexington since pesticide use began in the 1940's when the full ecological consequences of pesticides was not understood. 44 Type of Effects Which Might Result Several types of effects might occur which would impact the populations of non-target organisms They include 1) Direct kills. This involves immediate poisoning. 2) Interdependency Effects. This involves effects upon one species which occur indirectly by affecting species upon which it is dependent. For instance, nesting failure among birds may be produced by a sudden pesticide-induced drop in the insect food supply while nestlings are being fed. 3) Sublethal effects. Included here are those effects which do not directly result in death but which make the species more susceptible to predation, disease, or other natural hazards. Included here are effects which interfere with reproduction. This class of effects generally occurs at much lower dosages than the preceeding two effects and can be extremely difficult to verify. Reported Effects Associated with Malathion The application of malathion using L'LV techniques is intended to kill adult mosquitoes, but insecticide from such applications will enter the aquatic environment as well. Figure I.1 indicates the effects which have been reported for various concentrations of malathion in water. Data is taken from Reference 2 unless otherwise noted. It can be seen that concentrations lethal to fish, amphibians, and other aquatic organisms may result. Reference 11 points out that interference with the temperature selection ability of fish can lead to reproductive failure since spawning may occur in water which is too cold for proper development of eggs or young. The actual results observed from a particular application of malathion may depend upon the manner in which the material degrades. Some breakdown products are thought to be more toxic to fish than the original parent. compound The degradation pathway which is favored depends upon the temperature and acidity of the water - as well as the presence of othPi- chemicals or microorganisms The half-life of malathion in water varies with acidity and with the amount of biological activity. Half-life values between 2 days and 2 weeks. have been reported. Malathion degrades more slowly in acidic water. 45 FIGURE 1. 1 OBSERVED EFFECTS OF MALATHION IN AQUATIC ENVIRONMENTS 100 — 4--- lethal to fathead minnow (TL ) 10 _ 1 _ 1:1? lethal to tadpoles 4.3 r-I < concentration resulting from mosquito adulticiding — measured maximum for 3 fl. oz. /acre E tac, _ lethal to bluegill (TLm) fl. oz. /acre over water 0.5 meters deep 1 lethal to Caddisflies (LC50) reduces population of aquatic insects F1' .01 C.) reduces population of benthic organisms .001 affects growth rate of fish -< affects temperature selection of fish(Reference 11) < lethal to some zooplankton (EC50) .0001 _ 46 4 * Testing of water in Lexington by Kay Roop has shown that the water is almost always acidic (below pH 6) which should slow the degradation process If the frequency of application is comparable to the half—life, then concentrations in water can build up. Degradation products such as the malathion monoacids may be about 18 times more stable than malathion (Reference 2 p. 43) and hence may accumulate when the parent compound does not. 4 \\\ 47 REFERENCES 1. "Training Manual for Commercial Pesticide Applicator Certification in Massachusetts in Cat. 8: Public Health" In addition to guidance on pesticide use, this manual provides information on the biology of mosquitoes and on non-pesticide mosquito control techniques. Available for $4 50 from Bulletin Center, Cottage A - Thatcher Way, Univ. of Massachusetts, Amherst, Mass. 01003 2. U.S. Environmental Protection Agency, Initial Scientific and Minieconomic Review of Malathion, EPA-540/1-75-005, March 1975, 251 p. A comprehensive review of scientific literature on the chemistry of malathion and its effects upon humans, animals, and the environment. 3 U.S. Environmental Protection Agency, The Movement and Impact of Pesticide Used for Vector Control on the Aquatic Environment in the Northeast, Pesticide Study Series - 9, July 1972 A study of pesticide use for mosquito control in southeastern. Massachusetts. Contains an evaluation of the adequacy of state regulation of pesticides. 4. Weiss, B. and Laties, V.G. (ed.) , Behavioural Toxicology, Plenum Press, New York, 1975 5. Drenth, H.J. , Ensberg, Ivan F.G. , Roberts, D.V., Wilson, A. , "Neuromuscular Function in Agricultural Workers Using Pesticides", Archives of Environmental Health, vol. 25, No. 6, December 1972 6. "Pesticides Can Alter Human Brain Activity", Science News, vol. 114, No. 25, 16 December 1978 7, Gershon, S. and Shaw, F.H. , "Psychiatric Sequelae of Chronic Exposure to Organophosphorus Insecticides", Lancet, 1961, I: 1371-1374 48 I, ft, ; 11 ! • REFERENCES (continued) 8. Abou-Donia, Mohamed B. , "Delayed Neurotixicit of Phenylphosphono— thioate Esters", Science, Vol. 205, 17 August 1979 9. Revzin, Alvin M. , "Effects of Organophosphate Pesticides and Other Drugs on Subcortical Mechanisms of Visual Integration", Aviation, Space, and Environmental Medicine, Vol. 47, No. 6, June 1976 10. Revzin, Alvin M. , "Effects of Mevinphos (PHOSBRINR) on Unit Discharge Patterns in Avian Nippocampus", Aviation, Space and Environmental Medicine, Vol. 47, No. 6, June 1976 11. Domanik, Andrea M. , and Zar, Jerrold H. , "The Effect of Malathion on the Temperature Selection Response of the Common Shiner, Notropis cornutus (Mitchill)", Arch. of Environmental Contamination and Toxicology, Vol. 7, No. 2, 1978 • 12. East Middlesex 'iosquito Control Project, Annual Report of Activities, 1979 49