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