Molecular studies of Wolbachia and sex-determination genes in Australian Bactrocera species : complementary approaches to improved fruit fly control

Abstract

Bactrocera tryoni (Diptera, Tephritidae), the Queensland fruit fly (Qfly), is the most significant horticultural pest species in Australia. The Sterile Insect Technique (SIT), which relies on the release of vast numbers of irradiated sterile insects to suppress field populations, has been used in this species and, globally, is a successful pest management strategy for many insect species. For Mediterranean fruit fly, Ceratitis capitata, the incorporation of a genetic sexing system (GSS), that allows male-only releases, can increase effectiveness of SIT by 3-5 times. However, there is currently no GSS for B. tryoni. Furthermore, field performance of sterile flies, mass-reared and irradiated, can be generally lower than of wild individuals. Novel strategies such as Incompatible Insect Technique (IIT) exploit the reproductive manipulations of the maternally-inherited common endosymbiotic bacterium of insects, Wolbachia, to induce unidirectionally incompatible matings between uninfected field-females and released males carrying Wolbachia. While this method circumvents irradiation, a male-only release cohort is essential because females carrying Wolbachia are fully fertile; accidental release of infected females and thus inheritance of released Wolbachia in field populations would soon lead to a breakdown of the mating incompatibility essential for pest suppression. This thesis details the results of three fundamental and independent, yet complementary, experiments designed to investigate prospects for IIT and improvement of SIT, namely: an assessment of the incidence, prevalence and type of Wolbachia strains in Australian tephritid fruit fly species across their geographic range; a survey of the general microbiome of tephritid fruit fly species from different ecological niches and both natural and laboratory sources; an examination of genes expressed in early embryos of two Australian Bactrocera pest species, to generate molecular tools for GSS. Moreover, this work represents a valuable contribution to the ecological and epidemiological understanding of Wolbachia infection life cycles in insect communities, through discovery of a new model system for examining the distribution of Wolbachia along a climatic gradient, and the horizontal transmission of Wolbachia among a community of tephritid fruit flies. This work also presents important molecular studies of sex-specific gene expression over early embryonic development, with the aim of clarifying the function of M in tephritid fruit flies as models for the many insect species with similar sex-determination systems.

Date of Award	2014
Original language	English