Progeny quality of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae)reared on stored eggs of Homalodisca coagulata (Say) (Homoptera: Cicadellidae)

Authors: CHEN, WEN-LONG - NORTH DAKOTA STATE UNIV; Leopold, Roger

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2007
Publication Date: 6/1/2007
Citation: Chen, W., Leopold, R.A. 2007. Progeny quality of Gonatocerus ashmeadi (Hymenoptera: Mymaridae)reared on stored eggs of Homalodisca coagulata (Homoptera: Cicadellidae). Journal of Economic Entomology. 100(3):685-694.

Interpretive Summary: This study examines the use of stored glassy-winged sharpshooter eggs, killed by holding at 2°C for 5 days, to rear the small wasp, Gonatocerus ashmeadi. This wasp is an insect parasitoid that accounts for 80% of the parasitism of the glassy-winged sharpshooter (GWSS). To assess how well dead host eggs stored at 10°C for up to 70 days function in the rearing of this wasp, a number of different parameters associated with population increase were evaluated in the parent and two subsequent generations of progeny. The parasitism rate decreased with storage time, but more than 80% of the wasp eggs that were deposited in the host eggs stored up to 30 days emerged as adults. Storage of the eggs used to rear the parent generation of wasps longer than 30 days resulted in decreases in adult emergence, fecundity, and production of females. The reproduction rate of the first generation of progeny decreased after their parents used host eggs that were stored more than 30 days. Other population increase parameters such as doubling time and the mean time for generation turn over decreased only after their parents used eggs that were stored 60 days. The next generation of progeny was unaffected by having their grandparents use stored, dead host eggs for development. Our results show that up 30 days cold storage could be used for propagating wasp populations in a biological control program and that the detrimental effects of chilling host eggs in storage for over 30 days do not extend to the third generation.

Technical Abstract: This study assessed the effects of refrigerated storage on the suitability of the glassy-winged sharpshooter, Homalodisca coagulata (Say) eggs as hosts for propagation of the parasitoid Gonatocerus ashmeadi Girault. Development of the host eggs was terminated by chilling at 2°C for 5 days before storage was initiated at 10°C for up to 70 days. Parasitism, adult emergence rate, development time and sex ratio were used to assess the acceptability of the eggs as hosts after storage. Similar measures and also demographic growth parameters were used to assess the quality of the wasp progeny through the F2 generation. Host eggs stored 20 days remained fully acceptable to the wasps for attack. Although the parasitism rate decreased with storage time, > 80% parasitoid emergence was realized from eggs stored 30 days. After 70 days storage, adult emergence rate was decreased by 48%, fecundity decreased by 53%, female production 19%, developmental time was extended 3 d, and female longevity was shortened 5 d, respectively. The emergence pattern of F1 but not F2 adults varied with storage time. The F1 population had a type I survivorship pattern regardless of the length of storage. For the F2 generation, emergence rate, development and sex ratio did not vary with storage time when the F1 parents parasitized fresh host eggs. Demographic parameters for the F1 population showed that net reproductive rate was > 20 although it decreased significantly after the host eggs were stored for > 30 days. The intrinsic and finite rates of increase, population doubling time, and mean generation time decreased only after storage for 60 days. Our results show that short-term cold storage could be used for maintaining wasp populations in a mass-rearing program and that the detrimental effects of chilling host eggs in storage for over 30 days do not extend to F2 generation.