Resistant males had c. 1000-fold higher LC 50 values than susceptibles. Selection and backcrossing did not result in segregation of different levels of resistance in either sex. These results support the proposition that a single major sex-linked gene is primarily responsible for the high level of endosulfan resistance in this species. Endosulfan is the primary means of control because of its superior efficacy and lower environmental hazard than the current alternatives. A sound understanding of the mode of inheritance is desirable for monitoring resistance.
Males are dwarf and flightless.
The preliminary evidence from a single dose of endosulfan shows that, unlike females, males cannot be functionally heterozygotic. Establishing the mode of inheritance and genetic basis of the resistance should help to understand the population genetics of resistance in the field. Here we present data on the responses to endosulfan of males and females from reciprocal and repeated backcrosses. While the results for inheritance of the resistance in female beetles implicated a single major gene, the possibility of a second gene could not be overlooked. Hence we undertook the selection experiments reported here.