Optimization of Trissolcus japonicus cold storage methods for biological control of Halyomorpha halys

Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) has shown promise as a biological control agent for the invasive agricultural and nuisance pest, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). In addition to the need for laboratory research colonies, the possibility for rearing T. japonicus for classical or augmentative releases necessitates investigation into efficient rearing protocols with control over timing of production. Cold storage is a means to slow insects’ metabolism and cold temperatures can be used to manipulate when and how many parasitoids are available for use. Conditions of cold storage (i.e., temperature and photoperiod), duration of exposure to cold, nutrition, age, and sex of parasitoids can all affect the success of a cold storage regime. We tested how these factors affected mortality, realized fertility of females, sex of progeny, and development time for cold-stored adult and immature T. japonicus using previously frozen H. halys egg masses. Rearing adult T. japonicus at 8, 13, or 18 °C (10:14 h L:D) significantly increased longevity compared to 23 °C (16:8 h L:D); however, for females reared at 8 °C, 10:14 h L:D, we found sublethal effects on realized fertility and sex of their progeny. Adults with access to food survived at greater levels than those without food. We found high mortality of cold-stored immatures in all the ages and cold storage conditions tested. Additionally, differences in T. japonicus emergence from fresh and frozen H. halys eggs was assessed. This work can be used to compare the costs and benefits of cold storage for T. japonicus and will assist forecasting the emergence and sex of adult parasitoids after T. japonicus are cold stored.