Inheritance of dicrotophos resistance in greenhouse whitefly

We studied inheritance of resistance to dicrotophos in greenhouse whitefly,Trialeurodes vaporariorum Westwood (Homoptera, Aleyrodidae). Compared with females from a field-collected susceptible strains (S), females from a resistant strain (R) ofT. vaporariorum derived from heavily treated cotton fields had a 28-fold greater LC₅₀ to dicrotophos in laboratory bioassays. Concentration-mortality lines obtained from female progeny of reciprocal F₁ crosses (R_♀ XS_♂ and S_♀ XR_♂) were similar, suggesting that inheritance of dicrotophos resistance was autosomal and not influenced by maternal effects. Responses of F₁ female progeny were similar to those of the parental S strain, indicating that the resistance was partially recessive (degree of dominance, D, was −0.61). Mortality observed in female progeny obtained from a backcross (F_1♀ XR_♂) corresponded more closely to expectations derived from polygenic models than to expectations from a monogenic model. The estimated number of effective factors (sensu Lande, 1981) contributing equally to resistance was three.