SALT MARSH AERIAL LARVICIDING
General: There are approximately 23,000 acres of salt marsh on the North Shore of Massachusetts stretching from Boston north to the New Hampshire border. In our district, two species of salt marsh mosquitoes lay their eggs in the moist muddy areas associated with pans and depressions on the salt marsh and in stagnant ditches along the upper edges of the salt marsh. High run tides that typically occur once a month, as well as storm or rain events flood these areas and trigger the hatching of the eggs and emergence of mosquito larvae. The larvae then progress through 5 aquatic stages and can emerge as adult mosquitoes in a little as four days. Salt marsh mosquitoes are known for their aggressive biting behavior, even in the heat of daylight hours. If not controlled, they can be present in large numbers from June through September.
Notification: A Legal Notice will be published in February of each year giving general information about the applications and contact information for questions. The actual dates and times of applications are determined by surveillance data. Local health departments and the Massachusetts Pesticide Bureau will be notified by phone or fax prior to each application and a press release may be issued.
Pre-treatment
Surveillance: Salt marsh flooding events are monitored throughout the
summer. When a flooding event occurs larval surveillance is intensified.
Random dip samples are taken to determine specific locations of mosquito
breeding and population densities. Ideally, aerial applications are
scheduled immediately upon finding uniformed distribution of early larval
stages, as applications are most effective at that time and the window of
opportunity is short. Dip samples will also be taken from numerous
permanent stations, recorded and compared with post-treatment survey data
to determine the efficacy of the application.
Application: When pre-treatment surveillance data indicate an application is necessary, helicopters equipped with 80 gallon spray tanks and 250-300 micro rain drop nozzles mounted on a spray boom, capable of an 80 foot swath are employed for the application. The District's material of choice is Bti (Bacillus thuringiensis var. israelensis). Bti is a very selective, naturally occurring biological larvicide that is nontoxic to people, birds, fish, bees, and virtually all other insect species. Bti only effects mosquito larva and a few other closely related aquatic insects in the fly family.
