Location: Southern Insect Management ResearchTitle: A laboratory diet-overlay bioassay to monitor resistance in Lygus lineolaris (Hemiptera: Miridae) to insecticide commonly used in the Mississippi Delta
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2020
Publication Date: 7/13/2020
Citation: Portilla, M. 2020. A laboratory diet-overlay bioassay to monitor resistance in Lygus lineolaris (Hemiptera: Miridae) to insecticide commonly used in the Mississippi Delta. Journal of Insect Science. 20:4;1-13. https://doi.org/10.1093/jisesa/ieaa067.
Interpretive Summary: Insecticide resistance in plant bugs has been study with topical application of insecticides and several different glass-vial bioassays. Both bioassays rely on the use of green beans, broccoli, and wet floral foam as a source of food and water. Those bioassays are suitable for fast acting insecticides such as organophosphates and pyrethroids but not for neonicotinoids and sulfoxamine, where mortality at the insecticide rate resulted too low and mortality control resulted too high before and after 72 h of exposure, respectively. Therefore, this diet-overlay method was developed to assess glass-vial vs. diet-overlay assay assessments of the efficacy of the most common neonicotinoid, sulfoxamine, organophosphate, and pyrethroid insecticides (thiamethoxam, sulfoxaflor, acephate, and permethrin, respectively) used in the Mississippi Delta to control TPB.
Technical Abstract: A laboratory, diet-overlay bioassay was developed using a susceptible population of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), to study its susceptibility to thiamethoxam, sulfoxaflor, acephate, and permethrin insecticides. The diet-overlay bioassay was compared to the traditional glass-vial bioassay. We measured LC50 values by feeding adult known doses of insecticides dispensed on top of diet in a 10% solution of honey water for thiamethoxam and 10% acetone in water solutions for permethrin, acephate, and sulfoxaflor. Eleven experimental repetitions (11 sequential generations) used even-aged (1-2 d old) mixed sex insects obtained as eggs from separate cohorts. Both bioassays used dose-response (mortality) regression lines to calculate LC50 values for each insecticide at 6, 24, 48, and 72 h after exposure. Data from the glass-vial bioassay had higher variability among replicates for permethrin, sulfoxaflor, and thiamethoxam than the diet overlaid bioassay, for all evaluation times. In contrast, there was lower variability among replicates to acephate in the glass-vial assay compared to the diet-overlay assay. Dose-response observed on diet-overlay was better than those found on the glass-vial probably due to low control mortality (0-5%) compared to glass-vial (4-27%). The use of green beans, floral-foam, rolling vials, and insect handling made the existing standard method tedious to manipulate and difficult to handle large number of individuals. The non-autoclaved solid diet provides an opportunity to significantly reduce cost and increase the accuracy of experimental test results. In general, the baseline data provide a basis for future comparison to determine changes in resistance over time.