Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2008
Publication Date: 12/1/2008
Citation: Chen, W., Leopold, R.A., Boetel, M.A. 2008. Cold storage of adult Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) and effects on maternal and progeny fitness. Journal of Economic Entomology. 101(6):1760-1770.
Interpretive Summary: To aid in the mass-production of the egg parasitoid, Gonatocerus ashmeadi, for control of the glassy-winged sharpshooter, we developed a method to store adult wasps for subsequent use in a field release program. Three storage temperatures were examined and we found that at 2°C the wasps do not survive and if stored at 5 or 10° C too long, their life-spans are shortened. Other factors that are used to determine the fitness in the field of mass- produced wasps were examined in both the stored wasps and their progeny. Increasing the storage time at 10° C beyond the adult wasps' tolerance limits (20 days) showed that the stored generation had significant reductions in fertility, fecundity and the length of time spent egg laying. The incidence of parasitism by stored wasps of the host eggs was not adversely affected until they had been stored for 40 days. We also found a carry-over effect of the prolonged storage of the maternal generation that was expressed in the next generation. When cold storage of the adult parents was more than 20 days, we observed delayed development, decreased fecundity, reduced longevity and increased male production occurring in the next generation. However, these detrimental effects were not carried over to the third generation. Providing that the limits of cold tolerance of G. ashmeadi as defined in this study are not exceeded, our results show that short-term storage of adults could be used in a mass-rearing program.
Technical Abstract: 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 lifespan. The LT50 (i.e., length of storage time for 50% wasp survival) at 5°C was 14 d for males and about 29 d for females, while at 10°C was 32 and 39 d, respectively. Effects of adult storage at 10°C on other factors indicating fitness, such as fecundity, development time, parasitism, emergence and sex ratio, was examined on female wasps and their progeny at 10-day intervals for up to 60 d. Glassy-winged sharpshooter (Homalodisca vitripennis) 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 severely depressed after 60 d storage. A significant reduction in maternal lifetime fecundity occurred following 20 d storage and in the incidence of parasitism after 40 d. We also found a carry-over 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.