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HomeMy WebLinkAbout1980-05-15-PCAC-rpt.pdf RE IM FINAL REPORT 110 SELECTMEN' MA( 1 6 1980 MOSQUITO CONTROL IN LEXINGTON PEST CONTROL ADVISORY COMMITTEE TO THE LEXINGTON BOARD OF SELECTMEN MAY 15, 1980 1. Findin8s 4 This report is the result of the review of mosquito control practices conducted by the Pest Control Advisory Committee in the Spring of 1980. It proposes a deliberate approach to the development of a mosquito control program in Lexington. The Committee feels that the ultimate form of the program must depend upon the information gathered and the knowledge derived from the initial phases of the effort. New products and technologies should also be exploited whenever they allow the program to be improved. Hence the core of this report is not the specification of a detailed final solution to mosquito control, but the definition of a process by which that soulution should be arrived at. The order of preference of the various mosquito control measures and the manner in which conflicting concerns are reconciled should be well understood by those charged with carrying out the program. 1.1 Mosquito Control Issues in Lexington The status of mosquitoes as nuisance insects in the Town of Lexington has created a continuing interest in finding means to reduce or nullify their nuisance potential. Town government became involved in mosquito control efforts 36 years ago through funding of the activities of the East Middlesex Mosquito Control Project (EMMCP) , a governmental trust operating under the State Bureau of Reclamation. In recent years, criticism of EMMCP activities with respect to effectiveness and pesticide use led to the Town withdrawing from the Project. This decision left unresolved the question of whether or not there were mosquito control activities which the Town should undertake which would be acceptable in terms of pesticide use and environmental impact. The Pest Control Advisory Committee (PCAC) was appointed to investigate the options in this regard. 1.2 Realistic Expectations Realistic expectations are important in evaluating mosquito control options. Pesticide effectiveness figures which have been quoted from mosquito control project reports have sometimes given citizens the impression that most if not all mosquitoes can be eliminated by a modest investment in pesticide spraying. This is `unfortunately far from the truth. The climate and topography of Lexington have made it impossible to impact more than a small fraction of the total mosquito population with control efforts. These limitations were obvious last Spring when mosquito population levels during a rainy season were extremely high despite an ongoing mosquito control program conducted by EMMCP. In the judgement of the PCAC, all programs which involve modest expenditures will, regardless of the techniques employed, yield only slight reductions in Town-wide mosquito densities. In years of repeated heavy rains, substantial numbers of mosquitoes will almost certainly appear despite control attempts. Some level of mosquito annoyance is inevitable for housing placed in moist forested areas. Nevertheless, a carefully planned mosquito control effort may solve spot problems (e.g. by eliminating an isolated mosquito breeding site near residences) . It may also be capable of effecting a modest reduction in mosquito numbers below those which would otherwise result from a given level of rainfall. 1.3 Mosquitoes and Public Health The focus of previous Town mosquito control efforts has been nuisance abatement and not public health. A survey of 22 Lexington physicians and examination of data on mosquito-borne diseases in Massachusetts tends to support the conclusion that there are no mosquito-related public health objectives which require expenditure of Town funds. 1.4 Pesticide Risks for Human Health Careful compliance with federal label requirements and other elements of "good practice" can provide substantial protection against known adverse effects of pesticides upon human health. But it must be acknowledged that significant gaps exist in the scientific knowledge concerning the effects of pesticides upon the human nervous system or upon particularly susceptible persons. Materials are sometimes widely used for years before harmful effects are recognized and sufficiently documented to prompt regulatory action. For these reasons, pesticide use must be viewed as a matter of calculated risk. The decision to employ pesticides should hinge upon whether or not the benefits -2- to be derived outweigh the risk involved. One consideration which may be relevant 0 is whether the use of pesticides in a public program can replace any less desirable private applications. When a consensus cannot be reached on the benefits of an action, alternatives which respect individual choices should be sought. _ _ _ Regardless of the benefit/risk evaluation, proper program design requires minimizing risk factors such as the number of persons exposed, the frequency of exposure, the dosage, and the number of different pesticides used. Alter- native control measures and substitutes for chemical pesticides should be used to maximum advantage in pursuing these goals. 1.5 Ecological Effects of Mosquito Control Techniques The effect of mosquito control efforts upon non-target species should be considered for several reasons. Use of broad-spectrum pesticides can destroy the natural enemies of mosquitoes in an area. As a result mosquito populations can recover to higher densities than would have existed without pesticide use. Populations of beneficial insects which are important in controlling pests other than mosquitoes can be injured by pesticide use. Many non-target species such as birds and fish are highly valued for reasons which are totally unrelated to mosquito control. The chemical pesticides which were previously used in mosquito control efforts in Lexington are broad-spectrum materials which are toxic to a wide variety of organisms. They possess both lethal and sub-lethal effects which may cause declines in populations of non-target species. These effects cannot be reliably predicted from laboratory studies, but require actual monitoring in the field for detection. No monitoring of non-target species has accompanied previous pesticide use in Lexington. 1_ r. 2. Recommendations The following recommendations follow the general principle that those mosquito control measures which exert continual suppression upon mosquito numbers with the fewest controversial side effects should be implemented first and that other control measures should be utilized only as needed and only if provisions can be made for their safe and compatible use. 2.1 Baseline Nuisance Abatement. The Town should give first priority to 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 maintainance, and personal protection measures. Enlisting citizen cooperation through a public education program is an important part of these efforts. More detailed suggestions for program elements can be found in the working papers of the Committee. 2.2 Non-chemical Larvicides There are currently available certain larvicidal materials which are essentially free of hazard to humans and are unlikely to affect most non-target populations. Among such products are Altosid (methoprene) and Flit MLO larvicidal oil. Bacterial larvicides are under development which should be added to this list in the near future. Because these materials do not raise the concerns associated with chemical larvicides, they are preferred wherever use of larvicides is indicated. As with all pesticides, their worth will depend upon the coverage achieved and the timeliness of reapplications. Larviciding may not be worthwhile unless a significant fraction of the breeding sites which are causing a problem can be treated. Therefore the effective use of -4- A 6 these materials requires an understanding of which breeding sites are contributing to the nuisance problems in particular areas of Town. It is recommended that i ---cog the Town -tregurseer compile data which can be used to determine where such materials might be effectively used. If such areas are ti'auLLC_ found, provision for treatment should be made and the effectiveness of the treatment monitored. 2.3 Chemical Larvicides Use of chemical larvicides raises several of the previously discussed concerns for ecological impacts and human exposure. Alleviation of many of these concerns may be possible, but would require certain safeguards and monitoring capabilities which are currently unavailable. Therefore the PfAf: it is recommended that the use of chemical larvicides be deferred until after other control means have been implemented. If a role for chemical applications is then identified for which no alternative material is suitable, efforts can be directed toward creating a program structure which is suitable for the chemical use proposed. See section 2.5 for recommendations concerning such a strtictur'. 2.4 Chemical Adulticiding Adulticiding (spraying of pesticide into the air in order to kill adult mosquitoes) is Ole motn.vis blelement of mosquito controlAgilmgcEften the only e of which the public is aware. Yet authorities seem to agree that it is one of the 48-e least effective control measures in the Iu1ae r ui► and should receive lowest priority in most control programs. Adulticiding operations eem provide nuisance relief for only about two days following spraying. This is due to the fact that adult mosquitoes infiltrate from outside the sprayed area and continue to emerge from bredding sites within sprayed areas. STERNr Adulticiding is also one of the most controversial elements of mosquito control since it results in 0 inevitable impact upon non-target species (both terrestrial and aquatic) and results in unavoidable human exposure. No suitable alternative pesticides are apparent which could resolve these problems. In view of these considerations, it is recommended that Lexington's -5- - - r 2.5 Program Structure -3 1 Many legitimate interests affected by the decision to spray a chemical pesticide into the environment or alter a wetland for mosquito control purposes. The regional organization of mosquito control projects and their exemption from the Massachusetts Wetlands Protection Act has sometimes resulted in a feeling that mosquito control is being pursued with a single-mindedness which fails to adequately reconcile conflicting concerns. Hence any future decision to employ chemical pesticides or to transfer any significant program responsibility to a mosquito control project should be preceeded by development of a formal mechanism for public input and review of the program. It is impossible for a single town board or appointed commissioner to be aware of all the interests and concerns which should be included in the program planning process. The program should instead be planned by an appointed committee who would conduct a public hearing prior to approving any measures of broad environmental impact. This hearing would allow all concerned citizens to comment upon the proposed actions and would require the proponent of the actions to explain the benefits to be achieved and the safeguards to be employed in the work. Separate hearings should be conducted for each location and type of activity. 2.6 Initiating the Program In order to initiate the program outlined above the Selectmen should consider obtaining a summer employee who could be assigned the following responsibilities: 1) To initiate a public education program to enlist public support in nuisance abatement efforts. 2) To collect and map mosquito nuisance complaints received from residents. 3) To survey areas of complaints and to locate any mosquito breeding sources which may be causing the problem. A record should be made of each instance of mosquito breeding found. 4) Where indicated, to make a recommendation to the appropriate Town department or Board concerning specific actions to be taken to deal with specific problem sites. A mechanism for communicating with the appropriate persons and obtaining assistance should be developed. All data collected during the summer should he mapped or bound and filed for future reference.