Stable Fly Tolerance to Residues of DDT, Dieldrin, Malathion and Diazinon1

Abstract

In tests conducted to determine the insecticide tolerance of a strain of stable flies (Stomoxys calcitrans (L.)) from the U. S. Army Chemical Center, Maryland, females evinced an LC-50 of 1.3 mg. per square foot in the case of DDT, 0.8 mg. per square foot for malathion and 0.23 mg. per square foot for Diazinon® (O,O-diethyl O-(2-isopropyl-4-methyl-6 pyrimidinyl) phosphorothioate) 24 hours after a 15-minute exposure in treated pint Mason jars. A significantly lower tolerance to DDT was demonstrated by females held for 24 hours at 70°F. than was demonstrated by females held at 90. after a 15-minute exposure. This difference was not significant when similar tests were conducted with malathion. The World Health Organization test procedure for determining the susceptibility or resistance of adult mosquitoes to insecticides was highly satisfactory for testing adult stable flies. Groups of both sexes were tested with this procedure. The slightly higher DDT tolerance evinced by the males was not significant Females demonstrated a significantly higher tolerance to dieldrin than the males.