The competitive ability of three mymarid egg parasitoids (Gonatocerus spp.) for glassy-winged sharpshooter (Homalodisca coagulata) eggs
Parasitoid longevity, utilization of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) eggs of different ages, and progeny survival rates were determined in the laboratory for Gonatocerus ashmeadi Girault, Gonatocerus triguttatus Girault, and Gonatocerus fasciatus Girault (Hymenoptera: Mymaridae). Ovipositional behavior and aggression between females were investigated when all three species were simultaneously presented H. coagulata egg masses in the laboratory. Results from the longevity study demonstrated that when females were provisioned with honey-water solution, female G. ashmeadi survived up to 171.9% longer than G. triguttatus and G. fasciatus, whereas, survival was equivalent between G. triguttatus and G. fasciatus. Results from the egg age utilization study showed that G. ashmeadi, G. triguttatus, and G fasciatus most efficiently utilized eggs 1-6, 3-6, and 1-2 days of age, respectively, and that exploited egg age ranges overlapped between species. Gonatocerus ashmeadi parasitized a significantly higher (up to 45.0 and 62.6%) proportion of H. coagulata eggs aged 1-6 days of age compared with G. triguttatus and G. fasciatus, respectively. Additionally, in competition studies, overall parasitism by G. ashmeadi was significantly higher (up to 76.0%) compared with G. triguttatus and G. fasciatus. Results from behavioral observations of females concurrently searching for H. coagulata egg masses showed that G. ashmeadi allocated the greatest proportion of time to resting/grooming (26.5%) and oviposition (25.8%), while G. triguttatus allocated significantly more (up to 61.6%) time to resting/grooming compared with all other activities. Female G. fasciatus spent the greatest proportion of time resting/grooming (40.0%) and off leaves with H. coagulata egg masses (39.6%). G. ashmeadi and G. triguttatus allocated 2.1 and 1.3% of time to aggressively interacting and defending egg masses from congenerics, whereas, this was not observed for G. fasciatus. Results suggest that G. ashmeadi may show the most potential as a biological control agent of H. coagulata, and that successful widespread establishment and impact by G. fasciatus on H. coagulata in California is unlikely unless this species can efficiently exploit low density populations of H. coagulata in early spring when congeneric competition for egg masses is low. (c) 2005 Elsevier Inc. All rights reserved.