Molecular characterisation of the twisted wing endoparasitoid Dipterophagus daci (Strepsiptera) and its interactions with Wolbachia and multiple tephritid fruit fly host species
Australia hosts over 300 species of tephritid fruit flies, including the Queensland fruit fly, Bactrocera tryoni, Australia’s most significant horticultural pest. Australian tephritid fruit fly species have previously been found to be infected by two strains of the common insect endosymbiont Wolbachia. Wolbachia are maternally inherited endosymbionts in about 50% of insect species and can affect host reproduction and fitness. The phylogenetic incongruence of Wolbachia and their hosts indicates that horizontal transfer between species can also happen. Previously reported Wolbachia infections in Australian tephritid fruit fly species were unusual because they were detected in only seven out of 24 tested species (29 %) at low prevalence and titres and were restricted only to individuals of tropical Australia. This PhD thesis investigated these Wolbachia infections further by performing whole genome sequencing (WGS) of the field-caught Wolbachia-positive flies. This revealed an unexpected presence of almost complete mitochondrial genomes (mitogenomes) of another insect, in addition, to the expected fruit fly mitogenome in the genomic libraries of fruit fly. The additional mitogenomes belonged to a twisted-wing endoparasitoid, Dipterophagus daci (Strepsiptera), suggesting a possible link between Wolbachia and the presence of D. daci in tephritid fruit flies. This study therefore investigated the host-endoparasitoid-endosymbiont interaction between tephritid fruit fly species, Dipterophagus daci and Wolbachia. Overall, this study investigated and resolved the enigma of Wolbachia infections previously detected in tephritid fruit flies and presented evidence that the presence of Wolbachia in tephritid fruit flies was due to concealed early stages of parasitisation by D. daci. This reveals that the detection of Wolbachia in host taxa could be due to concealed parasitisation by strepsipterans or other endoparasitoids, and this could lead to incorrect assignment of Wolbachia to a wrong host. Additionally, it suggests that Australian tephritid fruit flies may not be naturally infected by Wolbachia therefore making them amenable for control using Wolbachia-based incompatible insect technique in the future. Furthermore, this study presents six D. daci mitogenomes and nine fruit fly mitogenomes which will be a useful source for future studies, in particular of the biology and ecology of the unique strepsipteran D. daci, and its impact on fruit fly population dynamics. This work also presents the first microbiome of a strepsipteran, which is a valuable contribution to the parasite microbiome studies
