Larvicide Program

Since April staff have been working nonstop surveying and treating for larva. July 5th-7th marked the largest aerial treatment BLSG has completed in 10 years. Total acreage covered was 5,496 in addition to the 2,408 acres treated on 5-12-17. Both treatments were a success with a 95% kill ratio. The weather has not been in our favor this season. It was an extremely wet spring, early summer and even now reaching the end of July. All prime conditions for mosquito breeding. As we move into the middle of summer, conditions are slightly improving as the flood plains are receding leaving vernal pools and drainage ditches full of anopheles larva. Recently the district has had a significant emergence of adult mosquitoes. This emergence was due to the excessive amount of rain we received in the last week. Adults were emerging from small puddles, wet lawns & fields. Conditions resembled a sponge, absorbing enough water to breed mosquitoes yet not enough to effectively treat.

Mosquitoes generally lay eggs in shallow, standing water such as the edges of wetlands, flooded fields or floodplains, and even stagnant water in gutters, old tires, or flower pots. When the eggs hatch (which can range from several days to several years later, as conditions dictate) larvae appear. Four larval stages of development occur, after which adults emerge and fly. 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 control all the more difficult.

The ideal situation is to control the life cycle in the larval stage. This involves application to water (by plane, helicopter, or backpack sprayer) of an organic pesticide (Bacillus thuringensis, or Bt) that closely targets mosquito larvae with little to no environmental impact. The timing and location of application are critical and when it works, it works very well and is quite safe. But it is complex. First, we need to know where there are dense populations of larvae, and that involves broad field surveys over thousands of acres. When prime locations are identified, a small plane or helicopter flying at low altitude and speed must drop controlled amounts of Bt over a narrow band of water that often is hidden by dense vegetation. The pilot works in concert with one or more ground observers and often has to follow very irregular water contours. Larval control is complex and not always successful and that is where control of adults is needed.


helicopter 1


BLSG Larvicide Coordinators Repot:


BLSG Mosquito Report

To view the 2016 BLSG Larval count data sheet select the following link:

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