Monitoring Resistance of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) to Insecticides by Using Encapsulated Artificial Diet Bioassay

Abstract

The novel ingestion bioassay method was developed for detecting and monitoring resistance of <i>Euschistus heros</i> by encapsulating an artificial liquid diet using Parafilm^®. This methodology was compared with the tarsal contact (vial test) and topical application methods for thiamethoxam, imidacloprid, and lambda-cyhalothrin. The best bioassay method for the neonicotinoid insecticides thiamethoxam and imidacloprid was ingestion. For pyrethroid insecticide lambda-cyhalothrin, the best result was obtained by topical application. Using the best bioassay method for each insecticide, the susceptibility to these insecticides was monitored in 30 populations of <i>E. heros</i> collected from soybean crops in Brazil from 2018 to 2020. High variations in susceptibility to thiamethoxam (resistance ratios, 1.6-22 times), imidacloprid (resistance ratios, 1.6-22 times), and lambda-cyhalothrin (resistance ratios, 5-40 times) were detected among the evaluated <i>E. heros</i> populations. In order to monitor the susceptibility of <i>E. heros</i> to insecticides, diagnostic concentrations were defined based on the LC₉₉ of the susceptible reference population: 5.65 µL of a.i./mL for thiamethoxam, 12.45 µL of a.i./mL for imidacloprid, and 0.20 µg of a.i./insect for lambda-cyhalothrin. Subsequently, we select an <i>E. heros</i> strain resistant to neonicotinoid insecticides and another to lambda-cyhalothrin. The resistance ratios obtained after seven selection cycles were 66, 41 and 44 times for thiamethoxam, imidacloprid and lambda-cyhalothrin, respectively.