Cold tolerance of adult African fig flies, Zaprionus indianus (Diptera: Drosophilidae)

African fig fly (AFF), Zaprionus indianus (Gupta) (Diptera: Drosophilidae), is an invasive pest that has established in temperate regions in recent years. Overwintering success is a critical factor underlying the potential geographic distribution of insects, yet the cold tolerance of AFF has not been extensively characterized. Here, we characterized cold tolerance and its plasticity in adult AFF originally collected from central Kentucky, a mid-latitude state with relatively mild but variable winter conditions. Specifically, we measured survival after acute cold shock and critical thermal minimum (CT_min), as well as how these traits respond to cold acclimation and rapid cold hardening (RCH). Cold acclimation, either throughout development or restricted to the adult stage, significantly enhanced survival after cold shock, as nearly all adults acclimated to 18°C survived a 1-h cold shock at −5°C, while none of the adults acclimated to 25 or 28°C survived. Cold acclimation similarly improved CT_min, as acclimation of adults to 18°C decreased CT_min by approximately 2°C compared to adults acclimated at the highest temperature (28°C). Developmental acclimation also lowered CT_min, and in this case, the acclimation response was stronger in males than in females. Finally, cold tolerance was improved by RCH. In both males and females, as little as 1 h at 6°C significantly improved flies' ability to survive subzero cold shocks. Together, our findings show that both long-term acclimation and RCH can improve AFF's ability to withstand cold. Also, the level of cold tolerance we report is comparable to other temperate drosophilids, suggesting this species' range may not be as limited by its cold tolerance as originally presumed.