Cold storage of adult Gonatocerus ashmeadi (Hymenoptera: Mymaridae) and effects on maternal and progeny fitness

Abstract

Storage of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) adults at 2,5, and 10°C showed that these parasitoids do not survive at 2°C for 5 d, and exposure to 5 and 10°C shortens their life span. The lethal time (LT)50 (i.e., length of storage time for 50% wasp survival) at 5°C was 14 d for males and ≈29 d for females, whereas at 10°C was 32 and 39 d, respectively. Effects of adult storage at 10°C on other factors indicating fitness, such as fecundity, developmental time, parasitism, emergence, and sex ratio, were examined on female wasps and their progeny at 10-d intervals for up to 60 d. Glassy-winged sharpshooter, Homalodisca vitripennis (Germar), eggs were used as hosts for propagation of this wasp and for assessing its oviposition and fecundity. Increasing adult storage time decreased the length of the ovipositional period for the maternal generation, and oviposition was decreased by 90% after 60-d storage. A significant reduction in maternal lifetime fecundity occurred after 20-d storage and in the incidence of parasitism after 40 d. We also found a carryover effect caused by storage of the maternal generation that was expressed in the F1 generation. When cold storage of the adult parents was ≥20 d, we observed delayed development, decreased fecundity, reduced longevity, and increased male production occurring in the F1 generation. Reduced fitness of the F1 generation was also expressed as a decrease in net reproductive rate (R0) and an increase in mean generation time (Tc). However, none of these deleterious effects were evident in the F2 progeny that descended from grandparents that had experienced cold storage. Damage caused by indirect chilling injury and/or induced maternal aging occurring during storage can account for the decreased fitness of maternal and F1 generations. Providing that the limits of cold tolerance of G. ashmeadi as defined in this study are not exceeded, our results show that short-term cold storage of adults could be used in a mass-rearing program.