Effects of sustained-release methoprene and a combined formulation of liquid methoprene and Bacillus thuringiensis israelensis on insects in salt marshes

Aquatic insects are an important component of the food web in salt marshes, therefore it is necessary to test whether pesticides used to control mosqu itoes in salt marshes are safe for nontarget insects. We tested the nontarg et effects of a combined formulation (duplex) of Bacillus thuringiensis isr aelensis (B.t.i.) and liquid methoprene (an insect development regulator) o r sustained-release methoprene pellets (Altosid(R) pellets) by applying the se materials to replicated salt marsh ponds at maximum label rates. Untreat ed ponds served as controls. We measured effects of the pesticides by reari ng immature mosquitoes (Aedes dorsalis) and water boatmen (Trichocorixa ret iculata) in predator-exclusion cages and by monitoring uncaged populations of invertebrates using replicated sweep-net samples. Both pesticides killed caged mosquitoes, and the activity of the Altosid(R) pellets continued thr ough 99 days. There were no detectable effects of either pesticide on the s urvival or maturation of T. reticulata, or on abundances of uncaged inverte brates. The long-term activity of the pellets could help minimize mosquito abatement activity in salt marshes where there are breeding birds or endang ered species. However, other studies suggest that this advantage needs to b e balanced against the risks that sustained-release formulations could lead to development of resistance in mosquitoes or that initially undetected no ntarget effects could build over time.