Performance of Leptopilina japonica Novković and Kimura (Hymenoptera: Figitidae) Under Fluctuating Temperature and Humidity

The parasitoid Leptopilina japonica Novković & Kimura (Hymenoptera: Figitidae) is a natural enemy of the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae), which is a significant pest in berry and fruit production. Both species originate from East Asia and after its initial detection in Europe in 2019, L. japonica has quickly spread and has established more northwards in several countries. Therefore, the potential of L. japonica for natural regulation of D. suzukii needs to be evaluated under various climatic conditions. This study is the first to examine the life history traits of L. japonica under fluctuating temperature and humidity conditions relevant in Central Europe, one of its new distribution areas and that from its main host D. suzukii . Average values for early (16.1°C–27.2°C) and late (12.3°C–23.9°C) summer days in Germany, during which host populations begin to increase or reach their peak, respectively, were simulated in the laboratory. Single pairs of wasps were mated and regularly provided with fresh hosts ( D. suzukii L2‐larvae) from emergence until death under the conditions of early and late summer in comparison to standard rearing conditions (permanent 23°C, 60% humidity). Parasitized hosts were further incubated under these conditions until emergence. The development rate did not differ between early summer and the control group, but was somewhat delayed under the cooler conditions of late summer. At this regime, however, the lifespan, lifetime fecundity, proportion of female offspring, and apparently also mating success were higher. These findings indicate the best performance of the parasitoid during the peak of its host's population density toward the end of the season and are also consistent with current observations that L. japonica is most common in late summer. In summary, analyses of thermal performance should account for fluctuating conditions in order to more reliably predict a parasitoid's field performance.