Submitted to: Arthropod Management Tests
Publication Type: Other
Publication Acceptance Date: 1/2/2004
Publication Date: 10/1/2004
Citation: McKenzie, C.L., Murphy, B.C. 2004. Toxicity of Agri-50 to Crawler/2nd Instar whitefly nymphs using a tomato plant-based bioassay, 2003. Arthropod Management Tests 29:L16 3 pp. http/www.entsoc.org/Protected?AMT/AMT29/Text/amt29.asp?Report=L16 (report). Interpretive Summary: A petri dish bioassay system was developed to hold single detached tomato leaves infested with sweetpotato whitefly, Bemisia tabaci (Gennadius) Biotype B for extended periods of time (egg to adult) to determine temporal toxicity of Agri-50. Agri-50 was extremely toxic to the crawler/2nd instar stage with LC90 values of 0.54%. Whitefly nymph mortality significantly increased over time (0.075% increased from 10% to 63%), but leveled off 7 days after treatment with no more appreciable mortality occurring. Further testing is needed to determine effects of Agri-50 to older SPW nymphs and adults.
Technical Abstract: A petri dish bioassay system was developed to hold single detached tomato leaves infested with sweetpotato whitefly (SPW), Bemisia tabaci (Gennadius) Biotype B for extended periods of time (egg to adult) to determine temporal toxicity of Agri-50. A hole was cut in the lid of a polystyrene petri dish) to facilitate ventilation and ultra-fine screen mesh was used to cover the hole to prevent SPW escapes. Polystyrene conical tubes were filled with a plant tissue culture water agar enriched with a N-K-P (9-45-15) fertilizer mixture. Whole tomato leaflets were selected from plants and pruned for bioassays. Tomato leaves were cut with a razor blade so that only the terminal leaf of the leaflet remained and would easily fit in the petri dish. Tomato leaves tended to show stress (wilting) initially, but usually acclimated within 24-48 hours and developed roots within 7-14 days. Agri-50 solutions were applied using an ultra-low volume spray device consisting of a spray platform that held a pressurizable spray bottle at the proper distance and angle to provide uniform and repeatable spray coverage to each petri dish. Measured amounts (200 µl) of pesticide solution were placed in individual test tubes as parafilm was wrapped around the top of the test tube to insure a tight fit. The spray bottle was pressurized to ~ 10 psi with 20 strokes of the pump mechanism for each application. Uniform infestations of SPW were caged for 24-48 hours to deposit eggs (25 to 50) on the tomato leaf bioassay. Adult SPW and cages were removed and eggs were allowed to hatch and nymphs developed to the crawler/2nd instars. Nymphs were counted prior to application. Serial dilutions of Agri-50 (0.075 ' 1.2%) were prepared in ddH20 plus a ddH20 control. Abaxial and adaxial leaf surfaces were each sprayed with 200 µl of solution and controls were sprayed with ddH20 alone. Conical tubes with treated bioassay leaves infested with SPW were placed upright in a Percival Scientific incubator at 25 ± 1° C and photoperiod 16:8 (L: D). Whiteflies were counted 1, 3, 7, 14, and 21 DAT or until all adults had emerged. Each concentration was replicated 5 times and bioassays were repeated four times. Relationships between mortality and concentration of Agri-50 were evaluated by probit analysis. Differences between LC values were determined by overlapping fudicial limits. Data were analyzed by the General Linear Models (GLM) procedure, and differences among treatment means were determined by Ryan-Einot-Gabriel-Welsch multiple-range test (REGWQ) at ' = 0.05. Agri-50 was extremely toxic to the crawler/2nd instars SPW stage. SPW nymph mortality significantly increased over time (0.075% increased from 10% to 63%), but leveled off 7 days after treatment with no more appreciable mortality occurring Further testing is needed to determine effects of Agri-50 to older SPW nymphs and adults.