Optimising irradiation dose in mass‐produced Queensland fruit fly, Bactrocera tryoni, for sterile insect release: the incorporation of residual effects on F1 progeny

The sterile insect technique (SIT) is a potential tool for the management and eradication of incursions of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Mass‐produced B. tryoni are irradiated during the pupal stage to induce reproductive sterility. As increasing irradiation dosage results in declining fly quality, determining the lowest possible dosage that induces sufficient reproductive sterility is of particular interest. However, in calculating reproductive sterility, previous research has not considered carryover irradiation effects to F₁ progeny. To test for these effects, B. tryoni pupae were exposed to one of five target dose ranges: 0, 20–25, 40–45, 60–65, or 70–75 Gy. Upon adult eclosure, fly quality was assessed using standard quality control (QC) measures: adult eclosure rates, flight ability, sex ratio, and longevity under nutritional stress. No effect of irradiation dose on any of the QC measures was found. Residual fertility was assessed by measuring larval eclosure failure for all doses. For the 0–45 Gy doses, mortality was measured during development of F₁ progeny and larval eclosure rates were measured in F₂ progeny. For irradiated females, irradiation dose significantly affected egg production, as well as increasing mortality during pupation of F₁ progeny. For irradiated males, irradiation dose strongly affected larval eclosure of F₁ progeny and, similar to females, mortality increased during pupation with higher doses. Our results suggest that residual effects of irradiation dose decreases F₁ progeny viability and current estimates of residual fertility for B. tryoni underestimate the actual residual fertility. We conclude by synthesising our results with the previous findings and we propose that the target irradiation dose for B. tryoni may be lowered to 55–60 Gy.