Field Studies of House Fly Resistance to Organophosphorus Insecticides1

Abstract

Applications of Diazinon® ( O,O -diethyl O -(2-isopropyl-4- methyl-6-pyrimidinyl) phosphorothiate) or ronnel (Korlan) for more than 5 years in New Jersey dairy barns resulted in decreased effectiveness in house fly ( Musca domestica L.) control with these materials. Flies were collected from these barns and subsequently exposed in the laboratory on residual deposits of Diazinon,ronnel, DDT, and lindane. Resistance to these compounds was found in fly populations from these barns and from more than 20 other barns located up to 5 miles from the study barns. Resistance was less near the edge of the dairy farming area in the county and at the greatest distance from the study barns. Cross resistance to Diazinon, ronnel, lindane, and DDT was shown throughout the area, with highest resistance to DDT. In the study barns a large population of the flies present before an insecticide application proved to have a lower level of resistance than the smaller number of flies present soon after an insecticide application. Thus, highest resistance was correlated with greatest amounts of insecticide in the barn and highest kills of susceptible flies. In one barn a similar reduction in fly population and an increase in resistance resulted when manure supporting heavy fly breeding was removed from box stalls. Observations in Sussex and Salem Counties also showed increasing Diazinon resistance and usually in proportion to Diazinon use. Some cross resistance to ronnel and high cross resistance to DDT and lindane were found in these areas. All evidence shows that DDT, lindane, and related materials will not give control where organophosphorns resistance exists. Dimethoate (O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate), and malathion were unsatisfactory in practical field control where resistance to Diazinon and ronnel was appreciable. At other locations this material gave 4 to 6 weeks of control.