Submitted to: Society for Cryobiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/3/2007
Publication Date: 12/1/2007
Citation: Leopold, R.A., Chen, W. 2007. The latent expression of chilling injury in the F1 progeny of the parasitic wasp, Gonatocerus ashmeadi [abstract]. Cryobiology. 55(3):376-377.
Technical Abstract: Chilling beneficial insects to be used in the biological control of agricultural pests is often employed during their mass production, accumulation, and/or shipping prior to field application. Gonatocerus ashmeadi, is an egg parasitoid that attacks the glassy-winged sharpshooter (GWSS), a vector of Pierce’s disease which causes the destruction of an large array of high value agricultural and ornamental plants. This parasitoid and related species are being tested for possible use in aiding in the control of GWSS. Our earlier studies confirmed that storing these wasps within the host GWSS eggs yielded greater survival when the temperature was cycled daily under a stepwise regime of 4.5, 6.0 and 7.5 °C changing every 8 h. [R.A. Leopold, W. Chen, G.D. Yocum, in: M.A. Tariq et al. (Eds.) Proc. Pierce’s Disease Symp., San Diego, CA (2004) 124-127]. Post-storage quality is of great concern when biological control agents are submitted to low non-freezing temperatures. Previous reports indicate that a variety of beneficial insects displayed reduced emergence, lifespan and/or reproduction following cold storage [R.A. Leopold, in: G.J. Hallman & D.L. Denlinger (Eds.) Temperature Sensitivity in Insects. Westview Press, Boulder, CO (1998) 235-268]. For this reason, we examined the post-storage quality of the parental through the F2 generation of G. ashmeadi using the stepwise cooling regime. Our studies indicated that GWSS eggs parasitized by G. ashmeadi can be stored up to 20 days without affecting emergence, survival, development, or progeny quality through the F2 generation. After 30 d of storage, survival of the parental generation was decreased by 24%, the developmental time was extended 4 d, and the fecundity of the F1 females decreased by 32%. After 40 d of storage, only 12% of the wasps emerged from their host eggs, 44% of the females were sterile, and the production of males by the non-sterile females increased by 155%. The F1 female progeny of these stored parents subsequently exhibited a 70% reduction in parasitism of host eggs and a 73% decrease in overall fecundity. Chilling also delayed the peak emergence of the parents but not of either the F1 or F2 generations. Examination of the F1 and F2 populations by demographic analysis also confirmed that the F1 generation was affected by 30 d of chilling of the parents but the damage did not extend to the F2 generation. Expression of reduced fitness by progeny of parents exposed to a stressful environment has been observed in a wide variety of organisms (e.g. maternal effects). Most studies report exposure of an environmental stress to the adult parent and this damage is passed to the progeny. With G. ashmeadi, the exposure to cold stress occurs while the wasps are still immature and within their hosts. Whether the damage is directly imparted to the developing wasps or indirectly through a damaged host has yet to be resolved. (Source of funding: USDA-ARS. Conflict of interest: None declared.)