Egg-surface bacteria deter oviposition by the oriental fruit fly Bactrocera dorsalis

Finding a suitable oviposition site is a challenging task for a gravid female fly, since the hatched maggots have limited mobility, making it difficult to find an alternative host. The oriental fruit fly, Bactrocera dorsalis, oviposits on many types of fruits. Maggots hatching in a fruit that is already occupied by conspecific worms will face food competition. Here, we showed that maggot-occupied fruits deter B. dorsalis oviposition and that this deterrence is based on the increased β-caryophyllene concentration in fruits. Using a combination of bacterial identification, volatile content quantification, and behavioural analyses, we demonstrated that the egg-surface bacteria of B. dorsalis, including Providencia sp. and Klebsiella sp., are responsible for this increase in the β-caryophyllene contents of host fruits. Our research shows a type of tritrophic interaction between microorganisms, insects, and insect hosts, which will provide considerable insight into the evolution of insect behavioural responses to volatile compounds.