Frequencies of organophosphate resistance-associated mutations in the acetylcholinesterase gene of field collected olive fly (Bactrocera oleae) populations under different insecticide regimes

Geographical distribution and frequencies of organophosphate-resistant Ace alleles and morphometric variations in olive fruit fly populations

BACKGROUND

In the Mediterranean basin, organophosphate (OP) insecticides have been used intensively to control olive fly populations. Acetylcholinesterase (Ace) is the molecular target of OP insecticides, and three resistance-associated mutations that confer different levels of OP insensitivity have been identified. In this study, genotypes of olive fly Ace were determined in field-collected populations from broad geographical areas in Turkey. In addition, the levels of asymmetry of wing and leg characters were compared in these populations.

RESULTS

Our study revealed the existence of a genetically smooth stratification pattern in OP resistance allele distribution in the olive fly populations of Turkey. In contrast to earlier findings, the frequency of Δ3Q was found to be lower in the Aegean region, where the populations have been subjected to high selection pressure. Results based on the morphological differences among the samples revealed a similar pattern for both sides and did not demonstrate a clear separation.

CONCLUSION

The frequencies and geographic range of resistance alleles indicate that they were selected in the Aegean coast of Turkey and then spread westward towards Europe. One possible explanation for the absence of morphological asymmetry in olive fly samples might be the presence of modifier allele(s) that compensate for the increase in asymmetry.

Tebufenozide resistance is associated with sex-linked inheritance in Plutella xylostella

The diamondback moth (DBM), Plutella xylostella (L.), is a major pest of cruciferous crops. Tebufenozide, a novel nonsteroidal ecdysone agonist, exhibits good efficacy and has played an increasingly important role in the control of Lepidopteran pests in China. For its resistance management, the genetic basis of tebufenozide resistance was studied using a laboratory selected resistant strain of DBM (resistant ratio, RR = 268). A series of crosses with laboratory susceptible and resistant strains revealed that tebufenozide resistance in this pest was partially biased toward female heredity, with a large difference in RR for F1 (RR = 29) and rF1 progeny (RR = 147). The dominance calculated for these 2 cross progeny was -0.788 and 0.09, respectively. Further analysis showed that the susceptible male and female larvae were similar in their sensitivity to tebufenozide, but the resistant female larvae showed significantly higher resistance than the resistant male larvae. The heredity of tebufenozide resistance in DBM might be linked with the W sex chromosome, which suggested that DBM has the ability to develop high levels of resistance to tebufenozide. This is the first report of sex-linked inheritance of tebufenozide resistance in P. xylostella (L.).