COMPATIBILITY OF SELECT INSECTICIDES WITH NATURAL ENEMIES OF THE GLASSY-WINGED SHARPSHOOTER AND OTHER PESTS

• Author(s): Henneberry, Timothy; Morse, Joseph; Toscano, Nick; Castle, Steven; Naranjo, Steve; Prabhaker, Nilima;
• Abstract: The toxicity of two insect growth regulators (IGRs), buprofezin and pyriproxyfen; three neonicotinoids, acetamiprid, imidacloprid and thiamethoxam; and three conventional insecticides, bifenthrin, fenpropathrin, and chlorpyrifos; were tested in the laboratory for compatibility with egg parasitoids (Gonatocerus ashmeadi, Gonatocerus triguttatus) of glassy-winged sharpshooter (GWSS), Homalodisca coagulata and against Aphytis melinus (A. melinus), an endoparasitoid of armored scale insects found on citrus in California. Most of the selected insecticides tested are used against GWSS and other pests on citrus and grapes. Survivorship of adult parasitoids on citrus leaves with residues of these insecticides (within Petri dishes) was determined after 24, 48 and 72h. Our results indicated that a number of insecticides tested are toxic to the egg parasitoids, Gonatocerus spp., as well as to A. melinus under laboratory conditions. Results from this study allow ranking of the eight insecticides based on their increasing toxicity as follows for Gonatocerus spp.: fenpropathrin > pyriproxyfen > buprofezin > imidacloprid > thiamethoxam > acetamiprid > bifenthrin > chlorpyrifos. All insecticides tested were highly toxic to A. melinus. In additional studies, higher concentrations of imidacloprid and thiamethoxam were found to be toxic over time to two predators, Geocoris punctipes and Orius insidiosus. Results from laboratory studies suggest that both systemics, imidacloprid and thiamethoxam, may not preserve these parasitoids as much as expected. To understand these bioassay results with the two systemics, further studies included the quantification of imidacloprid and thiamethoxam in both the parasitoids and the test citrus leaves by ELISA kits. Results indicated the presence of varying levels of these two compounds in the parasitoids as well as in citrus leaves suggesting that although parasitoids are non-plant feeders, they were exposed to the systemic chemicals. Further research is underway to determine how the parasitoids are exposed to the two systemics. Relative numbers of GWSS and its natural enemies from Riverside were determined using two sampling methods, collection of fresh GWSS egg masses on two host plants (citrus and willow) and using yellow sticky cards. Relative numbers of the pest (GWSS) and beneficials (Gonatocerus ashmeadii, Gonatocerus triguttatus and Ufens spp.) varied based on the sampling method. Seasonal patterns were obvious with higher parasitoid numbers in summer compared to fall collections with a parasitism rate at >90% based on the egg collection method. Few predators were observed on the yellow sticky cards.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium