Wetland management strategies that enhance waterfowl habitats can also control mosquitoes

Two studies in California wetlands and a third in Minnesota wetlands indicate that management practices designed to enhance habitat quality for waterfowl can concurrently reduce mosquito problems. In a seasonally flooded pickleweed wetland in Suisun Marsh, Solano Co., CA, we demonstrated that reducing plant-cover by 50% increased benthic densities of chironomid midge and dytiscid beetle larvae; these insects can be important in waterfowl diets. This manipulation also concentrated Aedes melanimon and Culiseta inornata mosquito larvae along wetland perimeters; thus, the need for control measures was greatly restricted spatially. A study in 9 experimental ponds in Suisun Marsh demonstrated that higher water levels could enhance populations of the macroinvertebrates important in waterfowl diets; general macroinvertebrate densities were higher at 60 cm depths than 20 cm or 40 cm depths. In contrast, Cs. inornata densities were lowest at 60 cm depths and highest at 20 cm depths. A study conducted in a perennial-water cattail wetland in Minneapolis-St. Paul, MN, demonstrated that a temporary water-level drawdown, designed to enhance waterfowl habitat quality of perennial-water wetlands, also reduced densities of Coquillettidia perturbans mosquito larvae. These mosquitoes disappeared immediately after the drawdown, but even after water depths were restored to pre-drawdown levels, significant numbers did not reappear until 4 years post-drawdown. Studies in 202 other Minnesota wetlands also demonstrated the susceptibility of Cq. perturbans populations to drawdown, but the impact of drawdown was greater in stands of emergent cattail than in floating cattail.