Insecticide-resistance in Culex pipiens fatigans.

The three main subspecies of the Culex pipiens complex-pipiens, fatigans and molestus-have similar "normal" levels of susceptibility to insecticides. C. p. fatigans larvae resemble those of anopheline mosquitos in sensitivity to dieldrin, but are more resistant to DDT; the adults are unusually resistant to chlorinated insecticides, but do not differ greatly from other species of mosquito in susceptibility to organophosphorus compounds.There is evidence of conversion of DDT to DDE in C. p. fatigans and other mosquitos, but this may well not be the only cause of resistance. Dieldrin-resistance in C. p. fatigans involves cross-resistance to HCH, but at a considerably lower level; the mechanism of resistance is still obscure. Resistance to organophosphorus insecticides has been observed; the cross-resistance to diazinon indicates that the mechanism is not solely one of carboxy-esterase detoxication.Mechanisms of inheritance of resistance have been investigated. The most recent results indicate the monofactorial inheritance of resistance by a single pair of nearly dominant genes on chromosome 2 for DDT-resistance and by a single pair of genes on chromosome 3 with intermediate dominance for HCH dieldrin-resistance.