Friday, October 10, 2008
Is Carlisle ready for mosquito control?
David Henley of the East Middlesex Mosquito Control Project (EMMCP) visited the Board of Health (BOH) on Thursday, October 2, to describe possible measures that could reduce mosquito populations in town. Currently, Carlisle is the only district municipality not using any project services. In late August, the Massachusetts Department of Public Health announced that two dead birds carrying West Nile Virus (WNV) had been found in Carlisle (see Mosquito, August 29). Several members of the public joined the meeting Thursday, missing the vice-presidential debate to learn more about active mosquito reduction.
A Carlisle Special Town Meeting in November 2000 overwhelmingly defeated a bid to join in mosquito control. At that time, concerns were raised that children and pets might be impacted, and that populations of insects that prey on mosquitoes could be reduced, leading to more mosquitoes. But according to Henley, mosquito control methods exist that do not impact humans, pets, or predator insects. With the risk of mosquito-borne disease on the rise, the BOH has decided to consider once again whether to bring a proposal to Town Meeting.
Higher West Nile risk this year
Everyone knows this has been a very long mosquito season with cool temperatures and plenty of rain. According to Henley, “There is a tremendous risk of West Nile. We’re seeing more [WNV]in mosquitoes than in any other year.” Two-thirds of Massachusetts communities have identified WNV in birds, and although there have been no human cases this year, the coast is not yet clear, as outbreaks typically occur in the fall.
The EMMCP, established in 1945, provides mosquito control to 25 participating communities located west and northwest of Boston. It offers a range of services for both larval and adult mosquito control, including sampling and testing, dispersion of controls from helicopters or roads, ditch and culvert maintenance, and public education. Member towns can choose which services to contract for, and payment is by the service, with a yearly $5,000 administrative charge. The project is 100% funded by its members.
Many types of mosquitoes
Massachusetts harbors 51 species of mosquito, and “most have some ability to transmit disease,” said Henley. For control purposes, mosquitoes are classified as those that develop in the spring wet season; those that develop in summer in wet areas such as river flood plains; marsh mosquitoes which incubate amidst cattails and emerge in June or July; and the eastern equine encephalitis (EEE) mosquito which over-winters in the larval state in cedar swamps. Henley notes there is a cedar swamp in Bedford, and a Bedford resident died of EEE in the 1980s. Fortunately, no significant outbreak of EEE is likely this late in the year.
Variety carrying West Nile common throughout region
The culex mosquito that carries WNV over-winters in the adult state in heated garages, barns, culverts, tunnels, and other areas that do not freeze. As a result, it is common even in urban areas. While some mosquitoes can travel for several miles, the culex typically stays within about ¼ mile of where it hatches. Larvae require 10 to 14 days of wet conditions to develop. It is not a buzzy, active mosquito, so victims are often unaware they are being bitten and may not think to apply repellants.
Areas close to the Concord and Sudbury Rivers have been pinpointed as especially mosquito-infested, and Henley notes that Bedford holds the district record of over 15,000 mosquitoes collected in one trap. The traps use light and dry ice or water to attract mosquitoes. Other insects are also monitored, as are larvae populations.
Bacteria pellets used against mosquito larvae
According to Henley, a large data base has been built over time, providing evidence for the safety and effectiveness of various control methods. Results have been obtained with helicopter dispersion of Bti (Bacillus thuringiensis israelensis), a bacterial larvicide that has been used on over 3,800 acres of wetlands in 15 communities within the district. “It is very specific to mosquitoes,” said Henley. “There is no harm to fish, amphibians, or other insects.” It is dropped in corn cob granules from helicopters using mapped data from mosquito collections to ensure maximum impact. There are no restrictions on usage as it is non-toxic to humans. On smaller wetlands it can be distributed from a truck.
Other programs treat catch basins and adult mosquitoes. Catch basins can contain tens of thousands of mosquito eggs and larvae. Bacillus sphaericus is the preferred agent because it remains in the water over several generations, whereas Bti breaks down in 24 to 48 hours.
Adult mosquitoes controlled with pyrethroids
Control of adult mosquitoes is typically through a pyrethroid aerosol sprayed from trucks or aircraft. The pyrethroids can be toxic to other animals so are used lightly and sprayed after dusk. One possibility for Carlisle would be spot application on vegetation around playing fields, but Henley said the town would not be a good candidate for wider control because of limited road access. Only nine communities in the district use adult mosquito controls.
Ditches and culverts cleaned
Other services of EMMCP include ditch maintenance and culvert clearing. The project is released from some of the regulations governing wetlands invasion, but Henley noted his group will coordinate with local conservation commissions and limit work areas if requested. Public education is also offered, including press releases, notices of spraying, programs for schools and speakers on various topics.
Costs are $15,000 to $25,000
Henley presented two sample proposals for Carlisle. The first would provide surveillance, catch basin treatment, and wetland surveys for $15,000 to plan for future active control. For an additional $10,000, the town could begin helicopter Bti application over 500 acres to kill larval mosquitoes. The applications are most effective if undertaken in early- to mid-spring, and BOH Chair Jeff Brem raised a concern that if the town chose to pursue that option, funding might not be in place in time for the coming spring.
Katherine Fink of Daniels Lane questioned how long the surveillance would be required. Henley explained that Bti application would be most cost-effective if a year of information on mosquito populations and water depths were available. While Carlisle has 1,060 acres of wetland, only half might provide the right environment for breeding. He added, “Bti is the right pesticide for Carlisle. It costs money to use a helicopter, but it’s the only way in an area with a lot of wetlands.”
Nancy Weiss of Brook Street asked whether mosquitofish, a fresh water fish that eats mosquito larvae, could be introduced, or other natural controls used. Henley said that Mass. Fish and Wildlife would not allow a non-native fish species to be released into any interconnected waterway. Henley said that introduced dragonflies are ineffective because they cannot be maintained in sufficient density to make an impact. Others asked about backyard products, and were told that foggers might have some use for short-term perimeter control, but mosquito magnets emit a carbon dioxide plume which can attract more mosquitoes than are killed.
Mosquito control does not affect Lyme disease
As for Lyme disease, Henley reported that mosquitoes are his bailiwick, not ticks. “Nobody (in state government) is really doing deer tick control” because no good methods currently exist. “It’s a huge problem,” he added, “not least for my crew” which has found Lyme disease to be an occupational hazard.
Weiss urged the BOH to move ahead quickly, “We know mosquitoes are a problem in our town. We named the paper after them.” Eric Richards of East Street agreed, noting he has three young children and “we’ve seen what carnage mosquitoes have done on outside activities.” BOH Chair Jeff Brem pointed to the defeat of the last mosquito initiative eight years ago and suggested, “If we go to Town Meeting, please speak on our behalf.” He added, “It looks like prevention and larval spray is the way to go” and said that further discussion will take place at a BOH meeting in November. ∆
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