A PRELIMINARY STUDY ON PARASITISM OF HOMALODISCA COAGULATA EGG MASSES BY GONATOCERUS ASHMEADI AND G. TRIGUTTATUS

• Author(s): Leopold, Roger; Chen, Wenlong; Morgan, David;
• Abstract: Parasitoid wasps in the families Mymaridae and Trichogramattidae are the most common natural enemies of the glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say), in its native range (Turner and Pollard 1959) and in California (Phillips 1998). Among its natural enemies, three egg parasitoids, Gonatocerus ashmeadi, G. triguttatus, and G. morrilli are important species being widely studied. The egg parasitoid, G. ashmeadi, is a mymarid wasp that accounts for 80-95% of the observed parasitism on the sharpshooter eggs in California (Phillips 2000). In Texas, GWSS eggs were highly parasitized by G. triguttatus throughout the year, but G. ashmeadi and G. morrilli were present in much lower numbers (Jones 2002). Classical biological control typically relies on propagation of natural enemies via mass-rearing to accumulate large quantities of beneficials for eventual release and establishment of field populations (Miller 1995). In the absence of practical techniques for propagation of the wasps via artificial methods, mass-rearing of these parasitoids mainly depends on a supply of host eggs also produced by a mass-rearing system. When mass-rearing and releasing parasitoids, such as G. triguttatus and G. ashmeadi, it is very important to understand the fundamental biological characteristics of the insects including reproduction, development, and host-wasp interaction. An investigation by Jones (2002) showed that egg parasitism by Gonatocerus ssp. on GWSS eggs varied with respect to type of plant the sharpshooters used as their ovipositional host in the field. Furthermore, microscopic particles called brochosomes are placed by the female GWSS around its egg masses Hix (2001), Rakitov (2002). Jones (2002) observed that these brochosomes clearly slowed down the time that G. triguttatus spends in completing its oviposition on GWSS egg masses. Irvin and Hoddle (2001) investigated egg age preference of single G. triguttatus and G. ashmeadi females to GWSS eggs for a period of 2 hours. The interspecific competition for oviposition between these two wasps was also observed in laboratory by Hoddle and Irvin (2002). Other than these studies, little is known about the reproductive behavior of these species, the development of these two wasps within the GWSS eggs parasitized at different ages, and effects of host plants and brochosomes on wasp ovipositional behavior. Further investigation on the behavior of these two wasps will be valuable in maximizing their production for release as bio-control agents.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium