Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/12/2004
Publication Date: 12/1/2004
Citation: Leopold, R.A., Chen, W. 2004. Parasitism of the glassy-winged sharpshooter: Functional responses and super-parasitism by the egg parasitoid, Gonatocerus ashmeadi. In: CDFA Pierce's Disease Control Program Research Symposium, December 7-10, 2004, Coronado, California. p. 128-131.
Technical Abstract: The functional responses and super-parasitism by the egg parasitoid, Gonatocerus ashmeadi, on Homalodisca coagulata eggs were related to host age and density when studied under laboratory conditions. Parasitism of glassy-winged sharpshooter (GWSS) eggs, 1-, 3-, 5-, 7-, and 9-d-old, was measured at 22 +/- 1 deg. C and under 10L:14D regime. For each host age, 10-60 eggs were exposed to an individual parasitoid for 24 h. The functional responses for the parasitoids to host eggs of all age groups most closely fit the type II and III models of Hollings (1959) and Hassell (1978) which relate to the elapsed time for accomplishing the behavioral events associated with parasitism of the host as modified by host density. The instantaneous attack rate by parasitoids on 1-d-old host eggs, as specified in the type III model, was significantly greater from that of the other ages. This rate was also greater in the type II model but was not statistically significant. The total number of host eggs parasitized varied significantly with host density and age of the eggs, but not when analyzed by a host x density interaction. Host age and density, as well as the host x density interaction, contributed significantly to the differences found in length of development time of G. ashmeadi within host eggs. The wasps exhibited a tendency towards super-parasitism at relatively high parasitoid-to-host ratios. The maximum number of parasitoid eggs found in a single host egg was 18. The development time and eclosion of the parasitoids had no correlation with parasitoid-to-host ratios. Frequencies of super-parasitism for G. ashmeadi displayed an aggregated distribution over all observed host densities.