Comparison of protein sources for cost-effective production and post-production operations of Queensland fruit fly sterile insect technique programs

The sterile insect technique (SIT) is used to suppress outbreaks of Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), the most economically damaging horticultural pest in Australia. Successful SIT programs require cost-effective production and release of high-quality insects. Yeast hydrolysate (YH) is a standard source of protein in the adult diet used in production and post-production operations of Q-fly SIT. YH is expensive, and so my aim was to find cost-effective alternative protein sources that might fully or partly replace YH. This study includes six experiments, comparing the performance of YH with potential alternative low-cost adult diets, including (1) commercial ‘Mubarqui’ diet (MD) (used for the SIT programs of the Mexican fruit fly); (2) protein-rich flours (soy, hemp, chickpea); and (3) plant- and dairy-based protein isolates (soy, hemp, and whey) (separately or in combinations). Observations were made of diet consumption, fecundity, hatch rate and reproductive organ development as key mass production quality parameters; and flight ability, mating and remating as key pre-release quality parameters. YH outperformed MD, each protein-rich flour and all of the plant- and dairy-based protein isolates in reproductive performance. Despite having good flight ability, Q-flies supplemented with MD, protein-rich flours, and protein isolates did not produce any eggs suggesting a crucial role of micronutrients in YH. To investigate whether alternative protein sources could at least partially replace YH, we conducted assays in which each protein source was mixed with YH (90:10, 80:20, and 50:50). However, all the combinations were found to be inferior to YH alone, suggesting that the deficiencies of alternative proteins are of macro scale.