Studies on Egg Parasitoids of Homalodisca vitripennis (Hemiptera: Cicadellidae): Biology, Sex Ratio Dynamics, and Distribution Across Southern California
Various aspects of the biology, sex ratio allocation, and host specificity of several species of egg parasitoids of the glassy-winged sharpshooter (GWSS), H. vitripennis (Germar), were studied. The distribution and prevalence of egg parasitoids of GWSS were investigated in an experiment conducted at six field sites over two years. Most of the observed parasitism was attributed to two species of Gonatocerus, G. ashmeadi Girault and G. walkerjonesi S. Triapitsyn, with the former producing most of the parasitism in interior southern California and the latter being predominant at coastal sites.
Biological traits of G. deleoni Triapitsyn, Logarzo & Virla and Pseudoligosita plebeia (Perkins), two potential candidates for biological control of GWSS, were investigated. Gonatocerus deleoni's average parasitism rate on 1-8-day-old eggs was 45.7% but this was significantly affected by the age of the egg, ranging from 1.4% to 69.9%. G. deleoni was able to develop in eggs of GWSS and Homalodisca liturata Ball, but was unable to develop on eggs of Graphocephala atropunctata (Signoret) or Erythroneura elegantula Osborn. When provided honey and water, water alone, or no food or water, P. plebeia adult females lived an average of 64.1, 2.3, and 2.0 days, respectively. Pseudoligosita plebeia were able to successfully parasitize GWSS eggs (1-8 days old), with higher parasitism in young host eggs (1-3 days old) than in old host eggs (5-7 days old). An increasing trend in offspring production was seen for P. plebeia from adult age 2 to 26 days followed by a decreasing trend with offspring produced up to age 75. Pseudoligosita plebeia contained fewer mature eggs at younger ages (1 and 3 days old) than at older ages (5, 11, 15, and 31 days old).
We examined whether G. ashmeadi Girault produces precise sex ratios under a field setting. Our analyses show field collected G. ashmeadi tend to produce less female biased sex ratios with higher variance in male numbers than are shown in laboratory studies. We found significant effects of proportion parasitism and host density on sex ratio, while proportion parasitism had a significant effect on sex ratio variance.