Organophosphate resistance and allelic frequencies of esterases in the olive fruit fly Bactrocera oleae (Diptera: Tephritidae)

The polymorphic esterase loci, Est A and Est B, of a major agricultural pest, the olive fruit fly, Bactrocera oleae (Dacus oleae), were studied using a standard laboratory population (Ls) that had never been subjected to insecticides, two "resistant" populations (Rs and RRs) constructed after exposure of larvae to sublethal doses of the organophosphate insecticide dimethoate, and a field population (Fs) subjected to long-term pesticide exposure. Data showed that dimethoate, as a selective agent, was responsible for the induction of the changes in the frequencies of alleles of the Est A locus, whereas it did not affect the Est B locus. Our results also showed that the changes in the frequencies of some active alleles of Est A locus, observed in resistant populations, were similar to those found in the field population.