Submitted to: Biocontrol
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/29/2014
Publication Date: 2/15/2014
Citation: Krugner, R. 2014. Suitability of non-fertilized eggs of Homalodisca vitripennis for the egg parasitoid Gonatocerus morrili. Biocontrol. 59:167-174. Interpretive Summary: The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is a key vector of Xylella fastidiosa, the bacterium that causes Pierce’s disease of grapevines and other diseases of high-valued crops in the Americas. GWSS invaded California in the late 1980s and continues to threaten the $4 billion grape industry. Control measures for GWSS in California include an area-wide insecticide (i.e., imidacloprid) application program and release of natural enemies, but, despite such efforts, the geographic distribution of GWSS continues to expand. Virgin GWSS females deposit non-fertilized eggs and mated females need to re-mate to continue to produce progeny. Therefore, it is possible that egg parasitoids of GWSS, such as Gonatocerus morrili that is used in California to control GWSS, are utilizing non-fertilized eggs for reproduction in mass rearing facilities and/or field conditions, which may affect efficacy of the parasitoid for control of GWSS. Parasitoids failed to emerge as adults from non-fertilized eggs more often than from fertilized eggs, indicating that non-fertilized eggs were accepted by G. morrili females as suitable hosts for oviposition, but were relatively unsuitable for immature development compared to fertilized eggs. Results suggest that reducing rates of GWSS egg fertilization through a mating disruption or sterilization program will have a negative impact on control of GWSS by natural enemies.
Technical Abstract: Gonatocerus morrili (Howard) (Hymenoptera: Mymaridae) is a natural enemy used in California, USA to control glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). Virgin GWSS females deposit non-fertilized eggs and mated females can exhaust sperm reserves for egg fertilization. However, nothing is known about Gonatocerus spp. performance when using non-fertilized GWSS eggs. Host age preference for oviposition and suitability of non-fertilized GWSS eggs for G. morrili reproduction were investigated. Gonatocerus morrili parasitized all ages of GWSS eggs (1 to 8 days old) regardless if the host egg was fertilized or not. However, parasitism rates and parasitoid emergence were reduced in older (> 5-day old) non-fertilized host eggs compared to fertilized eggs. In choice tests (fertilized versus non-fertilized eggs), parasitoids failed to emerge as adults from non-fertilized eggs more often than from fertilized eggs. The results indicate that non-fertilized eggs were accepted by G. morrili as suitable hosts for oviposition, but were relatively unsuitable for immature development compared to fertilized eggs.