Larvicide Program

Mosquitoes generally lay eggs in shallow, standing water such as the edges of wetlands, flooded fields or floodplains, and even in stagnant water in gutters, old tires, or flowerpots.  Larvae appear when the eggs hatch, which can take from several days to several years depending on moisture and temperature conditions.  Four larval stages of development occur over the course of 8 to 10 days, after which adults emerge and fly.  After mating, adult females seek blood meals to nourish their eggs with protein, and that is when they become pests.  About 45 species of mosquitoes inhabit Vermont and each has its own favored habits and habitats. Through the course of a season, waves of different species will emerge, depending on conditions, making larval control all the more difficult.

The ideal situation is to control the mosquito life cycle in the larval stage.  This involves application to standing water of a biologic pesticide (Bacillus thuringiensis) that closely targets mosquito larvae with little to no environmental impact. The timing and location of application are critical as only larvae in the first three stages (which only last a few days) are affected.  But, when a larvicide treatment works, it works very well and is quite safe.  However, application location and timing are complex.  First, we need to know where there are dense populations of larvae.  That is determined by broad field surveys over the sixteen thousand acres of Class 2 wetlands in the district.  When locations with abundant 1st – 3rd stage larvae are identified, then larvicide treatment can be done, either via backpack sprayer carried on an all-terrain vehicle (if the area is small and accessible, i.e., not covered by dense vegetation) or via helicopter flying at low altitude and speed.  Because larval control is complex and not always successful, control of adults often is needed.  Please visit the Adulticide Program tab on this website for more information on that topic.

To view the OCW Larval count data sheets select any of the following links:

2019 BLSG Larvae Count Data Sheet

2018 BLSG Larvae Count Data Sheet

2017 BLSG Larvae Count Data Sheet

2016 BLSG Larvae Count Data Sheet

2015 BLSG Larvae Count Data Sheet

2014 BLSG Larvae Count Data Sheet

2013 BLSG Larvae Count Data Sheet

2012 BLSG Larvae Count Data Sheet