Interactions of Topically Applied Piperonyl Butoxide and Malathion in Producing Lethal Action in House Flies1

The nature of the antagonistic effects of piperonyl butoxide to the toxic action of malathion on house flies,Musca domestica L., was investigated. Malathion was topically applied to various sites on the house fly body with varying degrees of toxicity. The same phenomena occurred for the relative toxicity of malathion in combination with piperonyl butoxide. The antagonistic effects of piperonyl butoxide were demonstrated even when it was applied on a separate area of the integument, separated from malathion treatment site, in nearly simultaneous topical applications to individual flies. The antagonistic effects of piperonyl butoxide decreased slowly over a 30-hourperiod, when it was applied first, followed at varying time intervals by the toxicant. In the reverse order of treatment such antagonistic effects decreased rapidly over a range of 30 minutes between the applications of malathion and piperonyl butoxide. The application of piperonyl butoxide 1 to 2 hours before malathion markedly increases the magnitude of the antagonism observed for simultaneous applications.