Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2005
Publication Date: 2/1/2006
Citation: Prabhaker, N., Castle, S.J., Byrne, F.J., Henneberry, T.J., Toscano, N.C. 2006. Establishment of baseline susceptibility data to various insecticides for glassy-winged sharpshooter, homalodisca coagulata say (homoptera: cicadellidae) by comparative bioassay techniques. Journal of Economic Entomology 99:141-154. Interpretive Summary: Control efforts for the glassy-winged sharpshooter (GWSS) in California began in earnest in 2000 soon after the epidemic of Pierce’s disease of grapevines was identified in the wine grape region of Temecula (Riverside Co.) in southern California. Area-wide insecticide treatment programs began in Temecula in spring 2000 and were followed in subsequent years by programs in the Coachella Valley (Riverside Co.) and in Kern and Ventura counties. In addition, more localized abatement actions were carried out in a number of communities in the San Joaquin Valley in an attempt to prevent GWSS populations from increasing and spreading. With widespread exposure to a diversity of insecticides and insecticidal modes of action taking place, the current research was initiated to determine baseline responses of GWSS populations to insecticides as part of a resistance monitoring and management program. Regional differences in responses suggest intrinsic potential for increasing tolerance or resistance to some insecticides, and thus resistance management programs should be implemented where intensive insecticide use against GWSS is occurring.
Technical Abstract: Glassy-winged sharpshooter (GWSS), Homalodisca coagulata, adults from three locations in California were subjected to insecticide bioassays to establish baseline toxicity. Initially, two bioassay techniques, petri dish and leaf dip, were compared to determine the most useful method to establish baseline susceptibility data under laboratory and greenhouse conditions. Comparative dose-response data were determined by both techniques to endosulfan, dimethoate, cyfluthrin and acetamiprid. Toxic values were similar to some insecticides with both techniques but not for all insecticides revealing susceptibility differences among the three populations of GWSS. In subsequent tests, the petri dish technique was selected to establish baseline susceptibility data to various contact insecticides. A systemic uptake bioassay was adapted to estimate dose-mortality responses to a systemic insecticide, imidacloprid. A two-year comparison of toxicological responses showed all three populations of GWSS to be highly susceptible to ten insecticides, including chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid and thiamethoxam. In general, two pyrethroids, bifenthrin and esfenvalerate were the most toxic compounds, followed by two neonicotinoids, acetamiprid and imidacloprid. The LC50s for all insecticides tested were lower than concentrations used as recommended field rates. Baseline data varied for the three geographically distinct GWSS populations with the petri dish technique. Adult GWSS collected from San Bernardino county were significantly more susceptible to select pyrethroids compared with adults from Riverside or Kern counties. Adults from San Bernardino county were also more sensitive to two neonicotinoids, acetamiprid and imidacloprid. The highest LC50 values were to endosulfan, which nonetheless proved highly toxic to GWSS from all three regions. In the majority of the tests mortality increased over time resulting in increased susceptibility at 48 h compared to 24 h. These results indicate a wide selection of highly effective insecticides that could aid in managing GWSS populations in California.