Effects of past and current temperatures on the flight performance of invasive pest fruit flies (Diptera: Tephritidae): Climate change may facilitate movements of tropical species to higher latitudes

Little is known about how past and current thermal environment interact to determine dispersal in novel environments, and thus invasion potential of major agricultural pests. In this study, we tested experimentally how adult thermal history affects flight-related traits under diverse thermal conditions in three major agricultural pests of invasion concern: Bactrocera dorsalis, Bactrocera zonata and Ceratitis capitata. Across all species, the main factor affecting flight performance was body mass, with heavier individuals performing best. Both current and, to a lesser extent, past thermal environments affected flight performance and periodicity (flight interruptions), although their interaction was rarely significant. Furthermore, we show that 20°C acclimation can have deleterious effects regardless of thermal conditions during flight, particularly in Bactrocera females, which had decreased flight performance and increased flight periodicity when acclimated at this temperature. The thermal environment during flight affected both flight periodicity and performance mainly in females of C. capitata and B. dorsalis, while only flight performance was affected in B. zonata males. When compared to warmer temperatures, flight at 20°C tended to reduce flight performance, but flight periodicity increased at 30°C compared to 20°C. Overall, the flight performance of B. dorsalis was greater than that of C. capitata or B. zonata, regardless of the past and present thermal environment, but flight periodicity was lower in C. capitata. In all three species investigated, optimal flight performance occurs around 25°C, and flies will therefore cover more distance around this temperature. The lack of interaction between past and current thermal environments in these three species indicates that flight-related traits may have low thermal plasticity. Finally, our results suggest that a reduction in thermal variability and average temperatures increasing temperate areas by a few degrees with climate change may facilitate movements of tropical tephritid pests in new areas at higher latitudes.