Submitted to: Life Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2011
Publication Date: April 30, 2012
Citation: Greenberg, S.M., Lopez, J., Latheef, M.A., Adamczyk Jr, J.J., Armstrong, J.S., Liu, T. 2012. Toxicity of selected insecticides to onion thrips (Thysanoptera: Thripidae) using a glass-vial bioassay. Journal of Life Sciences. 6:428-432. Interpretive Summary: Onion thrips are a persistent pest of vegetables and cotton in the Rio Grande Valley. Young seedling cotton can be susceptible to damage from migrating onion thrips that increase on vegetables grown in the spring and then move to cotton when it is planted and emerging. We evaluated four relatively new insecticide active ingredients using a glass vial assay where the active ingredient is deposited on the inside of the glass vial. This procedure provides an evaluation of contact exposure of immature and adult onion thrips. The results were that an insecticide named Spinosad (Tracer®) was the most active compound, requiring less than one third of one microgram (mg) to cause a significant amount of mortality to onion thrips. This was followed by Spinetoram (Radiant®) at 4 to 6 µg/vial, Spirotetramat™ (Movento®) 6 to 14 µg/vial, and Formetanate hydrochloride® (Carzol®) 5 to 16 µg/vial. This information is useful in helping determine the most active insecticide to use, and documents the level of susceptibility or resistance the onion thrips may obtain from being exposed to multiple applications of insecticides when applied in vegetables and cotton.
Technical Abstract: Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), are important pests that are primarily controlled with insecticides on both onions and cotton in the Lower Rio Grande Valley of Texas. Resistance to various insecticides has been reported so data are needed on toxicity of insecticides related to efficacy and for resistance baseline determinations. Glass-vial bioassays were conducted to evaluate toxicity of selected insecticides against immature and adult onion thrips. Spinetoram (Radiant®), spirotetramat (Movento®), formetanate (Carzol®), and spinosad (Tracer®)were the insecticides used in the laboratory assessment with greenhouse-grown thrips reared on cotton, but originally field-collected from onions. The LC50 (95% Confidence Limits) values for contact with all the insecticides were significantly different, with spinosad being the most active (0.349 [0.294-0.409] µg/vial at 24 h) and formetanate being the least active (11.577 [5.108-16.877] µg/vial at 24 h). Data reported are useful for selecting insecticides with the highest activity for use in onion thrips control and for monitoring resistance of the thrips to insecticidal treatments in the Texas Lower Rio Grande Valley.