Electrophysiological and Behavioural Responses of Sexually Immature Female Bactrocera Tryoni to Microbial Volatiles From Enterobacteriaceae

Abstract The Queensland fruit fly (Bactrocera tryoni) is a major polyphagous pest widespread in Australia and several Pacific Islands. Bacteria present on the host plant phyllosphere supply proteins, essential for egg development and the sexual maturity of female fruit flies. We investigated the role of microbial volatile organic compounds (MVOCs) to attract sexually immature females. Four Enterobacteriaceae commonly found on the host plant and in the gut of B. tryoni were cultured under different pH conditions and their MVOCs collected with two different headspace volatile collection methods (Tenax® filter and solid phase micro-extraction (SPME) fibre) for chemical comparison. Using electroantennographic detection, we assessed the olfactory response of sexually immature females to MVOCs and identified bioactive compounds. The production of MVOCs was strongly influenced by species and pH. Four compounds were found to trigger consistent electrophysiological responses: 2-phenylethanol, isoamyl alcohol, indole and phenol. Klebsiella oxytoca produced the most indole, whereas Citrobacter freundii specifically produced phenol. Tenax extracts from K. oxytoca invoked the strongest antennal response and attracted the most sexually immature females among all four bacteria. Further tests with electrophysiologically active MVOCs at different ratios under different environmental conditions are needed to develop a specific female lure for B. tryoni.