COLD STORAGE OF THE ADULT STAGE OF GONATOCERUS ASHMEADI: THE IMPACT ON MATERNAL AND PROGENY QUALITY Project Leader:

The effect of storage of adult G. ashmeadi at 2, 5 and 10°C on maternal and the unstored progeny fitness qualities was examined. The maternal generation did not survive five d exposure to 2°C and those stored at 10°C survived longer than those held at 5°C. Oviposition of the maternal generation continued for 13 d after storage at 10°C for 10 or 20 d and for eight d for the wasps stored for 30, 40 or 50 d. After storage for 60 d, the parasitoids did not oviposit for the first two d and then there was only a four d oviposition period. Cold storage reduced the fecundity of the parents and their F1 progeny, but not the F2 generation. After 20 d storage, the fecundity of the maternal generation decreased by 47% and for 60 d storage, it was reduced 90%. The longevity of F1 parasitoids was also less than that of F2 parasitoids. After 30 d storage of the parents, the longevity of the F1 generation was reduced 49% as compared to a 10 d parental storage period. The F1 progeny of the stored female parasitoids developed about one d more slowly than that of the F2 and F3 generations. Moreover, cold storage caused a reduction in the incidence of parasitism by parental generation, but this effect did not extend to F1 and F2 progeny. Emergence of F1 parasitoids decreased as the length of storage of their parents increased. Further, the parental generation deposited more haploid than diploid eggs after storage for 20 d and after 50 d, production of males was increased by 132%. The sex ratios of the F2 and F3 generations did not vary with the storage duration of the ancestral generation. INTRODUCTION Cold storage can be a valuable tool in mass-rearing of biological control agents. It provides a steady supply of insects for research, yields flexibility and efficiency in mass production, allows synchronization of a desired developmental stage for releases, and facilitates availability to consumers (Leopold, 1998). Maternal survival and offspring fitness are of great concern when using cold exposure during production or storing of biological control agents. Some reports indicate that the quality of a variety of cold-stored pest and beneficial insects suffer by having reduced emergence, lifespan and/or reproduction (Leopold, 1998). The egg parasitoid, Gonatocerus ashmeadi Girault, is one of the most common natural enemies of the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). It accounts for 80-95% of the observed parasitism of sharpshooter eggs in California. As part of a control program, G. ashmeadi, along with two other mymarids, G. triguttatus Girault and G. fasciatus Girault, has been imported, mass-reared and released in California. However, there are two main problems that reduce the effectiveness of Gonatocerus spp. in control programs. One is that the native wasps do not build up rapidly enough to make an impact on the spring generation of H. vitripennis in the colder regions of central and northern California (Morse et al., 2005). Another problem is that effective mass production of these parasitoids can not be realized due to a shortage of H. vitripennis eggs caused by a reproductive diapause (Hummel et al., 2006), especially in the late winter season. Thus, it would desirable to store large numbers of parasitoids to meet these fluctuating demands. Methodology for cold storage of H. vitripennis and G. ashmeadi has been developed to aid the mass rearing of G. ashmeadi (Leopold and Chen, 2005; Chen and Leopold, 2007; Chen et al. 2007). We have also examined a number of fitness factors of G. ashmeadi and progeny performance following the use of these storage protocols. Using chilling-killed H. vitripennis eggs as hosts for rearing G. ashmeadi, Chen and Leopold (2007) found that wasp progeny quality was severely reduced when their parents were reared on H. vitripennis eggs that had been stored for 60 days before parasitization occurred. Further, by stockpiling immature G. ashmeadi within H. vitripennis eggs, quality of maternal and first generations also suffered significantly with the length of storage duration (Chen et al. 2007). In this study, we examined the post storage quality of the parental, F1, F2 and F3 generations of G. ashmeadi after storing the adult female parents to further understand chilling injury and its expression in this parasitoid. OBJECTIVES 1. Determine the survival of adult parasitoid following cold storage. 2. Determine the effect of cold storage on fecundity and subsequent development of the progeny. 3. Determine progeny quality by examining some fitness factors including parasitism, emergence and sex ratio.