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

• Author(s): Morse, Joseph; Toscano, Nick; Castle, Steven; Henneberry, Thomas; Naranjo, Steve; Prabhaker, Nilima;
• Abstract: To evaluate the compatibility of insecticides that have both a broad and limited spectrum of activity against biological control agents, laboratory studies were carried out to compare the relative susceptibilities of seven foliar and two systemic insecticides against four common species of beneficial insects: Aphytis melinus Debach, Gonatocerus ashmeadi Girault, Eretmocerus eremicus Rose & Zolnerowich, and Encarsia formosa Gahan. Evaluations with systemic insecticides also included two species of predators, Geocoris punctipes Say and Orius insidiosus Say. Foliar insecticides were evaluated by a petri dish technique across a range of concentrations to measure their effect on direct mortality of the parasitoids. A systemic uptake bioassay technique was used to determine the toxicity of systemics against the six species of beneficials. Insecticides tested are used against citrus and agricultural pests, and included acetamiprid, imidacloprid, thiamethoxam (all 3 are neonicotinoids); chlorpyrifos, (organophosphate); bifenthrin, cyfluthrin, fenpropathrin (all 3 are pyrethroids); and buprofezin and pyriproxyfen (two insect growth regulators = IGRs). Chlorpyrifos, a conventional organophosphate insecticide with broad-spectrum activity, was consistently the most toxic pesticide to all four species of beneficial insects tested. Among the pyrethroids, fenpropathrin demonstrated lower toxicity to parasitoids compared with bifenthrin or cyfluthrin. Acetamiprid, although efficacious against GWSS, exhibited fairly selective toxic characteristics to G. ashmeadi and E. eremicus until four days post-treatment while being toxic to A. melinus within 24 h after treatment. Aphytis melinus was the most susceptible hymenopterous parasitoid to all test insecticides. Buprofezin and pyriproxyfen, with a relatively narrow spectrum of activity, were less toxic to the parasitoids. Imidacloprid has been considered to be relatively selective, with limited impact on parasitoids because of its systemic activity. However, results from this laboratory study suggest that both systemics, imidacloprid and thiamethoxam, may not be as selective against parasitoids as was expected. To understand the bioassay results with the two systemics, quantification of imidacloprid and thiamethoxam in both the parasitoids and the test citrus leaves was evaluated using ELISA kits. Additional studies are underway in the laboratory to determine how the parasitoids are exposed to these two systemic materials through various routes of exposure. Selectivity of these two compounds to natural enemies is also being examined under field conditions. The results presented here will provide pest managers with specific information on the degree to which the tested insecticides are likely to be compatible with various natural enemies.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium