SALT MARSH AERIAL LARVICIDING

General:  There are approximately 23,000 acres of salt marsh on the North Shore of Massachusetts, stretching from Boston to the New Hampshire border.  Two species of salt marsh mosquitoes lay their eggs in moist muddy areas of pans, depressions, and 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  triggering the hatch of eggs and emergence of mosquito larvae. Larvae progress through aquatic stages and can emerge as adult mosquitoes in as little as four days. Salt marsh mosquitoes are known for there 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 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 sample dips are taken to determine specific locations of mosquito breeding and population densities.  Ideally, aerial applications are scheduled immediately upon finding uniform distribution of early larval stages as applications are most effective at that time and the window of opportunity is short.  Sample dips will also be taken from numerous permanent stations,  recorded, and compared with post-treatment surveys to determine efficacy off the application.

Application:  When pre-treatment surveillance indicates 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 Bacillus thuringiensis var. israelensis (Bti).  Bti is a selective, naturally occurring, biological larvicide and is non toxic to people, birds, fish, bees, and nearly all other insect species.  Bti only effects mosquito larva and a few other closely related aquatic insects in the fly family.

Post-treatment Surveillance:  Mosquito breeding areas that have been sprayed will be surveyed 24 hours after the application.   Numerous random sample dips will be taken as is necessary to determine the overall efficacy of the application.  Sample dips will be taken from  numerous permanent stations and recorded for comparison with pre-treatment survey.