Studies on the cross-tolerance to DDT-related compounds of a pyrethrin-resistant strain of Sitophilus granarius (L.) (Coleoptera, Curculionidae)

Abstract

A laboratory selected strain of Sitophilus granarius resistant to pyrethrins (×138) was also resistant to DDT (×29·5), when compared with a susceptible strain. Evidence is presented to show that resistance to these two toxicants was connected. Cross-tolerances were found to four compounds which are not readily dehydrochlorinated by some DDT-resistant insects. These compounds were: o-chloro-DDT (×40 to ×55), deutero-DDT (×29·5), Bulan (×22·4), and Prolan (×14·1). It was considered unlikely, therefore, that dehydrochlorination was a major factor conferring tolerance to DDT. A high cross-tolerance to Perthane (×76) and some tolerance to methoxychlor, both of which could be readily hydroxylated, supports a hypothesis of oxidative detoxication. However, a cross-tolerance to iso-DDT (×11 to ×15) and fluoro-DDT (×37·2) makes it likely that more than one mechanism is present. Differences in the mortality response with time between the resistant and susceptible strains are shown, both for the rapidly acting pyrethrins and the more slowly acting DDT-related compounds. These differences and the variation in slope of probit-logdose lines are discussed in relation to resistance assessments. © 1969.