The effects of bacterial probiotics fed to larvae of Queensland fruit fly (Bactrocera tryoni). Do they improve fitness and performance under the Sterile Insect Technique?

The Queensland fruit fly, Bactrocera tryoni Froggatt (Diptera, Tephritidae), is native to Australia, and is a pest and biosecurity threat to the $9 billion horticultural industry. B. tryoni is controlled using a range of tools including the Sterile Insect Technique (SIT). SIT involves area-wide, inundative releases of sterile insects to reduce reproduction in a wild population of the same species. Mass-rearing and irradiation of the pupae in SIT programmes reduces fitness and performance of the released sterile insects. Larval gut microbiota may influence health, fitness and behaviour of all phases of the B. tryoni life-cycle. It is feasible that domestication, mass-rearing and irradiation may impact the gut microbiota and affect the quality of the mass-reared fruit flies used in SIT programmes. Using live bacterial species of Asaia, Enterobacter, Lactobacillus and Leuconostoc isolated from the midgut of wild larvae as a probiotic supplement, we tested several fitness and performance traits of B. tryoni. These included larval development time, pupal weight, time to emergence of adults, sex-ratio, flight ability, survival in field cages and mating competitiveness. The addition of probiotics to the larval diet could lead to improvements in mass-rearing of B. tryoni used in SIT programmes such as, reduced development times, reduced costs of production, and increased competitiveness in the field.