Electrophysiological and Behavioural Responses of Virgin 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 female sexual maturity. We investigated the role of microbial volatile organic compounds (MVOCs) in attracting virgin females. Four Enterobacteriaceae commonly found on the host plant and in the gut of B. tryoni were cultured on different media (artificial and natural fruits), and their MVOCs were collected using two different headspace volatile absorbent materials (Tenax® filter and solid phase micro-extraction fibre; SPME), allowing to test for time and pH variations. The olfactory responses of virgin females to bacterial MVOCs were assessed via electrophysiology and behavioural assays. The production of MVOCs was strongly influenced qualitatively by the bacterial strain, the type of media and quantitatively varied with pH and time. Phenol was detected only from Citrobacter freundii (CF), while indole was found in all bacteria except CF. Indole production increased overtime in inoculated kiwifruits. D-limonene was detected from Enterobacter cloacae and Klebsiella oxytoca (KO) and associated with oranges and inoculated kiwifruit. Tenax extracts from KO invoked the strongest antennal response and attracted virgin females the most. Among the identified compounds triggering an olfactory response, D-limonene and 2-nonanone were both significantly behaviourally attractive whereas phenol, nonanal, isoamyl alcohol and some pyrazines appeared repulsive. This study provides a new foundation for developing a synthetic lure based on microbial volatiles to replace food baits targeting specifically virgin females.