Research and IPM

Determine the risk posed to native California sharpshooters and their respective indigenous parasitoids posed by the introduction and establishment of exotic mymarid parasitoids that have been released for the classical biological control of glassy-winged sharpshooter.

Produce a colored pictorial guide of all economically important California sharpshooters (native and exotic) and their associated hymenopterous parasitoids.

Host specificity testing results were further evaluated by comparing observed laboratory and field nontarget impacts. For G. ashmeadi, significant laboratory and field nontarget impacts were documented for STSS eggs on both the native plant jojoba and Eureka lemons. BGSS and GSS eggs on the different plant species were not acceptable hosts for G. ashmeadi. For G. fasciatus significant laboratory impacts for STSS eggs, minor impacts for GSS, and no impact for BGSS eggs was documented. However, nontarget impacts as predicted in the laboratory for G. fasciatus were not revealed in field surveys. Field collected sharpshooter eggs, reciprocal sentinel plant deployments, and laboratory tests confirmed Gonatocerus latipennis Girault and Polynema sp. (Hymenoptera: Mymaridae) as egg parasitoids of the BGSS (Fig. 3); Paracentrobia auriscutellum (Girault), Paracentrobia sp. (Hymenoptera: Trichogrammatidae), and Gonatocerus mexicanus Perkins (Hymenoptera: Mymaridae; Fig. 4) were confirmed as egg parasitoids of the GSS. Through the course of this work, a novel testing cage was designed for standardizing biological studies on arthropods; the oviposition preferences determined and a SoCal day degree model were constructed for BGSS.

Female BGSS oviposited into new growth, primarily the succulent tendrils and stems. The undersides of small leaves and petioles were also used for oviposition, but to a lesser extent. Mature stems, large- and medium-sized leaves and petioles were not used for oviposition. Two parasitoids, Gonatocerus latipennis Girault and a Polynema sp. (Hymenoptera: Mymaridae), were reared from BGSS eggs. Literature reviews revealed a deficiency of known natural enemies for G. atropunctata. Deployment of sentinel plants and reciprocal tests were implemented to further confirm the parasitization of BGSS eggs by these parasitoids.

Collectively, the Polynema sp. and Gonatocerus latipennis constitute the first documented parasitic natural enemies of BGSS eggs. A further examination, starting in January 2004, of the activity of BGSS and its parasitoids in southern California is under way. Blue-green sharpshooter adult activity reached its peak in July while biweekly samples of wild grape canes and tendrils revealed that peak emergence of blue-green nymphs and parasitoids occurred from mid-July to mid-August. No-choice tests with Gonatocerus ashmeadi Girault, a parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata, and BGSS eggs as part of a nontarget impact assessment have indicated that BGSS eggs are not used by G. ashmeadi.

More testing is planned for 2005 to confirm this. No-choice tests with G. ashmeadi and the native smoke-tree sharpshooter (STSS), Homalodisca liturata Ball, a native congener to GWSS, yielded no significant differences in percent parasitism of eggs when compared to the glassy-winged sharpshooter control.