Insecticidal activity of ring-fluorinated benzyl acetone analogs in Queensland fruit fly, a softer class of insecticides

Insecticides used to control fruit fly pests have been implicated in negative effects on natural enemies, human health and the environment. As potential ‘softer’ insecticides, natural compounds such as essential oils and their constituents have received increased attention as insecticide candidates. Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is the most economically damaging fruit fly species in Australia. Cuelure and melolure are plant-based attractants of males in Q-fly and many other dacine fruit flies and are structurally similar to benzyl acetone. We hypothesized that fluorination of benzyl acetone would introduce toxicity that could be exploited for insecticidal applications. Toxicity to Q-fly of nine fluorinated analogs of benzyl acetone as well as the known attractants cuelure and melolure was investigated. LC50 and LC90 values of the compounds were obtained using a surface-film assay method. Fluorination at the meta and/or para-position of benzene ring was found to increase toxicity to both Q-fly sexes. We further examined toxicity and short-range attraction to Q-fly using traps in outdoor cages. The nine fluorinated analogs of benzyl acetone were all highly toxic to male Q-flies, whereas cuelure and melolure were not. Some analogs were attractive to male Q-flies. None of the nine analogs, cuelure or melolure had an inhibitory effect on the proliferation of BEAS-2B human bronchial epithelial cells, suggesting very low or negligible mammalian toxicity. Fluorinated analogs of benzyl acetone have potential as new toxicants for Q-fly, and likely other insects, and some may also have attractive properties for cuelure-responding fruit flies.