Temperature experienced prior to adult emergence modulates adult cold tolerance of the invasive Tephritidae species Bactrocera dorsalis and Bactrocera zonata

Thermal conditions experienced prior to adult emergence can induce phenotypic plasticity that shapes adult stress tolerance in insects to allow overwintering. Such carry-over effects may be especially important for insect invasive species of tropical origin that are currently expanding their range into Europe temperate regions. We investigated how temperature during pupal development and prior adult emergence affects adult cold tolerance in two invasive tephritid species: Bactrocera dorsalis and Bactrocera zonata. Both species are considered important emerging pests of temperate regions, especially for Europe and their developmental plasticity that impacts cold tolerance may facilitate establishment and persistence under cooler environmental conditions. Laboratory reared pupae of both species were maintained under three constant temperatures (15 °C, 20 °C, and 25 °C). Cold tolerance of adults emerging from pupae maintained at different developmental temperatures was assessed by measuring the Critical Thermal minimum (CTmin) and Chill Coma Recovery Time (CCRT). Lower developmental temperatures prolonged pupal development in both species, although only B. dorsalis survival remained in high levels throughout the developmental temperatures exhibiting better cold performance than B. zonata in the immature stages. Overall, CTmin did not differ among developmental temperatures, species and sex. However, the interaction between temperature and species was significant indicating the different response of the two species on the development at lower temperatures. In both species adults emerging from individuals developed at 15 °C recovered faster from chill coma than those developed at 20 and 25 °C. Bactrocera dorsalis displayed stronger temperature-dependent variation and slower overall CCRT than B. zonata. Nevertheless, both species converged in recovery performance at 15 °C. This suggests that cooler temperatures during pupal development and prior to adult emergence enhanced adult cold response primarily through improved CCRT. The observed interspecific differences in CCRT reflect distinct cold tolerance patterns between the two species. Bactrocera dorsalis exhibited higher plasticity while B. zonata showed less developmental plasticity than B. dorsalis. These findings highlight that temperature during development and before adult emergence as a key determinant of adult response to cold temperatures and may contribute to invasion potential in tephritids. Incorporating these plastic responses into bioclimatic and pest risk models will improve predictions of invasion success, establishment probability, and range of expansion by driving overwintering success of those species. Developmental temperature prior to adult emergence regulates adult cold tolerance. Adults of Bactrocera dorsalis and Bactrocera zonata obtained from immatures developed at 15 °C recovered faster from chill coma than those developed at 20 °C and 25 °C. Bactrocera dorsalis displayed stronger temperature-dependent variation on cold tolerance than B. zonata.