Studies on Aqueous Suspensions of Insecticides. Part IV. The Behaviour of Mosquitos in contact with Insecticidal Deposits

Abstract

The behaviour of mosquitos in contact with deposits from aqueous suspensions of insecticides has been studied by allowing them to alight individually and measuring the time to the first flight.Anopheles stephensi females flew from all formulations of DDT on various materials after approximately the same time of 2 to 4 minutes, but subsequent kills were high only when the deposit consisted of small (less than 10 microns) particles readily available for pick-up.Mosquitos were also activated by contact with fresh deposits of BHC wettable powder P.520, but all died very quickly. They were not disturbed, however, by the vapour from BHC deposits, when contact was prevented, until in an advanced stage of intoxication. The time to the first flight from surfaces treated with BHC wettable powder increased as the deposits aged and varied with different materials according to the rate of loss by evaporation and/or sorption.Mosquitos remained in contact with deposits of chlordane, dieldrin, aldrin and toxaphene for more than 30 minutes.Experiments with a number of DDT analogues and BHC isomers indicated that lipoid solubility and molecular structure are two factors governing the rate of penetration of a compound.The reactions of other species tested were similar to those of A. stephensi but kills of Culex p. molestus were significantly different from those of the Anopheline species after contact with deposits from a DDT wettable powder.