Thermal Performance of Two Indigenous Pupal Parasitoids Attacking the Invasive Drosophila suzukii (Diptera: Drosophilidae).

Pachycrepoideus vindemiae (Rondani) and Trichopria drosophilae (Perkins) are among a few indigenous parasitoids attacking the invasive Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in North America. Both parasitoid species occur in California, whereas only P. vindemiae has been reported from Oregon. We compared the thermal performance of the California populations of P. vindemiae and T. drosophilae, and the Oregon population of P. vindemiae at eight constant temperatures (12.6-32.8°C). Both P. vindemiae populations could develop at all tested temperatures. T. drosophilae failed to develop at or above 29.6°C. This species was, however, able to develop at a diurnal temperature regime of 15-32°C, and survival was higher in older developmental stages. T. drosophilae was less tolerant to both low and high temperatures than P. vindemiae, whereas the Oregon P. vindemiae population was more cold-tolerant but less heat-tolerant than the California population in terms of offspring survival, development, and reproduction. To develop storage strategies for mass-cultured parasitoids, we compared the cold tolerance of immature P. vindemiae and T. drosophilae of the California populations at 12°C for 1, 2, or 3 mo, followed by a 23°C holding period. Successful development to the adult stage decreased as cold storage duration increased. Successful development, however, increased when cold storage was initiated during the older developmental stages for 1-mo exposure for both parasitoid species. The results are discussed with regards to parasitoid thermal adaptation and the potential use of P. vindemiae and T. drosophilae for biological control of spotted-wing drosophila.