Efficacy of the pyrethroid alpha-cypermethrin against Bactrocera oleae populations from Greece, and improved diagnostic for an iAChE mutation.

Background: The most important pest of olive orchards worldwide is the olive fruit fly Bactrocera oleae (Gmelin). Its control in Greece has been based on organophosphates (OPs), but their intense use has led to the development of resistance. A test previously developed to monitor the trait may not be as robust as originally thought. The pyrethroid alpha-cypermethrin has recently been registered for bait sprays, as an alternative to OPs.

Results: The susceptibility of 20 B. oleae populations to alpha-cypermethrin was examined. Variation was observed in their response, with LD(50) ranging from 0.14 to 3.28 ng insect(-1) and resistance factors from 2.3 to 54.7. Resistance mechanisms were investigated. Cytochrome P450 monoxygenase activities showed an association with resistance. Sequences in the domain IIS4-IIS6 of the B. oleae para-type sodium channel were also analysed, but no resistance-associated mutations were identified. Finally, a novel diagnostic assay able to reliably monitor the frequency of the iAChE G488S resistance mutation was developed.

Conclusion: This is the first attempt to evaluate the efficacy of alpha-cypermethrin against B. oleae from Greece. Data showed that it can be used effectively, but also highlighted the importance of continuous monitoring. The IIS4-IIS6 sodium channel region is the default area in which to look for resistance mutations if target-site resistance to pyrethroids arises. The application of the novel iAChE molecular diagnostic may facilitate the introduction of pyrethroids alongside OPs currently in use.