The Carlisle Mosquito Online

Friday, November 3, 2000


BOH hears options and risks of mosquito control project

With the new potential threat of mosquito-borne West Nile virus, the board of health is once again exploring whether Carlisle should join the Central Massachusetts Mosquito Control Project. At their October 24 meeting, Tim Deschamps, assistant superintendent of the project, explained the five stages of the project's mosquito control operation: larvaciding, water management, surveillance, public education and adulticiding for mosquito control. Twenty-nine towns have joined the project, excluding Carlisle, Concord, Westford and Acton and Deschamps pointed out that the other three towns are also considering mosquito control. The question of whether to participate in the project will be placed before Carlisle citizens at the Town Meeting on November 14 (Warrant Article 7).

Five stages of control

Stage 1 of mosquito control is directed at the larval stage, so that the need for spraying adult mosquitoes is reduced. Project workers place briquettes of Bacillus thuringiensis israelensis (BTI) in stagnant water where mosquitoes breed. BTI is a non-reproducing bacterium which, according to the Environmental Protection Agency, produces a substance that is toxic to mosquito larvae but has little or no effect on other aquatic life. Water management, Stage 2, consists of clearing ditches or culverts and man-made ponds to increase water flow, since mosquitoes need still, stagnant water to breed.

During Stage 3, monitoring mosquito populations in both the larval and adult stages helps to determine the appropriate methods to be employed. The project's program to educate the public about mosquitoes in Stage 4 is also an import part of the approach. There is a comprehensive website at with links to many related sites.

If larvaciding and water management measures are inadequate and populations of adult mosquitoes reach intolerable levels, spraying is the only remaining alternative and the most controversial part of the program. Hand-held or truck sprayers are used to reduce the adult mosquito levels in residential and recreational areas. The pesticide used is resmethrin, a synthetic pyrethroid. This presents a minimal risk to humans, pets and non-target species, according to literature found on the website. Deschamps stated that there is no evidence that it kills bees or birds. Spraying adult mosquitoes is done only when a town or townsperson requests it. The project determines if the mosquitoes are intolerable with a two bites per five-minute rule. The explanation brought some laughter from the audience of seven homeowners. Even if spraying is requested, it is sometimes denied if the project worker does not detect mosquitoes or if requests are received from the same person each week. Deschamp pointed out that any resident who desires exclusion from spraying can register with the project.

The project operates from March to September, surveying wet areas and doing the larvaciding. In response to a question about trespassing on private property, Deschamps explained that project workers, who have a two-year apprentice training and an average of 12 years of experience, are exempt from prosecution for trespassing under state law. The larvaciding is exempt from conservation commission actions, but Deschamps explained that the technicians do employ a 30-day notification. "Just because we are exempt, we don't run roughshod over neighborhoods," added Deschamps. Most work is done by hand and the project has only one tractor to service 29 towns. Deschamps pointed out that the Wetlands Protection Act would prohibit an untrained homeowner from placing larvacide in wetlands areas.

BOH considers risks

"I'm concerned that we've gone bare as long as we have," said Dr. Claudia Talland, the board of health physician. "We are being bad neighbors," she commented, adding that failing to join the project would be out of step with other communities.

"Is there a liability issue?" asked board of health chair Steve Opolski. Talland said that there might be, if we become the only town not participating.

"Are we trading one low risk event for another low risk event?" asked Opolski. Talland said that while there is no evidence of value in mosquito control for West Nile virus in Massachusetts, the discussion has to include Eastern Equine Encephalitis which has some presence. If the town does not join the project, it is also possible that the federal government, through the Center for Disease Control, may require us to do so.

Warrant Article 7 asks for the town to participate in the project at a cost of approximately $24,000 per year, which is funded by the state and deducted from the "cherry sheet" distributions to the town. The BOH will take a position on Article 7 before the Special Town Meeting.

2000 The Carlisle Mosquito