Subacute exposure to prallethrin modifies behavior of medically important vectors

Ultralow Volume (ULV) applications of mosquito adulticides have been widely used in public health programs due to their high success rates and relative safety. Traditionally, these programs have relied on sumithrin as the primary active ingredient and peperonyl butoxide as a synergist. Prallethrin has been added as a third active ingredient in a new and widely marketed, yet costly, adulticide; its intended effect is to modify mosquito behavior by causing a sublethal locomotor stimulation which increases the overall effectiveness of the ULV application. A randomized complete block design was used on plots in woodlot edges to test the effect of volatized prallethrin on various species of mosquitoes, sand flies, and ticks using a variety of traps baited with CO2 and light. Two prallethrin rates were used: a low use rate at the recommended level (1.24 oz/acre) and a high rate (12.4 oz/acre). No significant effects on trap catches of sand flies, mosquitoes, or ticks were seen. A laboratory spray system was constructed to simulate a ULV application to mosquitoes at field-relevant levels. Behavior of treated mosquitoes was then observed in a wind tunnel for orientation against an air stream. These results showed a locomotor stimulation, but only when liquid droplets came into direct contact with the mosquito integument. These results indicate that commercial ULV products with prallethrin are not producing this advertised behavioral effect without contact. This suggests that the price premium public health programs are paying for mosquito adulticides containing prallethrin, over traditional sumithrin-only adulticides, may not be justified.