Rearing Istocheta aldrichi (Diptera: Tachinidae) from field-collected Japanese beetle (Popillia japonica): methods to improve overwintering, adult emergence and longevity

Istocheta aldrichi (Diptera: Tachinidae) is a specialist parasitoid of the invasive Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae). Research and releases for biological control depend on field collecting parasitized hosts and rearing the parasitoid through diapause to obtain I. aldrichi adults. This study investigated how rearing practices before, during and after the seasonal overwintering period affected the proportion of I. aldrichi pupae that emerged as adults, the timing of parasitoid emergence, and their longevity. Increasing cold exposure duration during overwintering increased adult I. aldrichi emergence from puparia and reduced development time after transfer to warm conditions. Adult I. aldrichi emergence from overwintered puparia depended on interactions between overwintering environment (indoors vs. outdoors), spring thermal regime, and the timing of host collection in the previous season. Burying puparia in the soil in late summer/early fall resulted in higher subsequent adult I. aldrichi emergence. Manipulating spring temperatures in controlled environments allowed parasitoid emergence to be staggered over several weeks without reducing emergence success. Emergence under outdoor spring conditions was unreliable. Adult longevity was affected by temperature and diet: cooler conditions extended lifespan, honey-water increased longevity relative to pollen alone or honey-water and pollen together. These results provide a foundation to further improve I. aldrichi rearing techniques for use in experimental research and applied biological control of P. japonica.