Susceptibility of Euschistus heros and Dichelops furcatus (Hemiptera: Pentatomidae) to insecticides determined from topical bioassays and diagnostic doses for resistance monitoring of E. heros in Brazil

Abstract

The Neotropical brown stink bug, Euschistus heros (F.), and the green belly stink bug, Dichelops furcatus (F.) (Hemiptera: Pentatomidae), are the main sucking pests of soybean and maize in Brazil. Here, we characterized the susceptibility of populations of E. heros and D. furcatus to insecticides and define doses for resistance monitoring of E. heros. Stink bug populations collected in the seasons from 2018 to 2020 were exposed to technical grade insecticides in topical bioassays. Populations of E. heros presented low variation in the susceptibility to acephate (LD50 = 0.22–0.69 μg a.i./stink bug), thiamethoxam (LD50 = 0.0039–0.032 μg a.i./stink bug) and bifenthrin (LD50 = 0.021–0.10 μg a.i./stink bug), with resistance ratios < 8.2-fold in relation to a susceptible population. However, the same populations showed high variation in the susceptibility to lambda-cyhalothrin (LD50 = 0.023–0.35 μg a.i./stink bug) with resistance ratios from 3.1- to 15.7-fold. Populations of D. furcatus had a similar susceptibility to acephate (LD50 = 0.30–0.53 μg a.i./stink bug), thiamethoxam (LD50 = 0.070–0.14 μg a.i./stink bug) and lambda-cyhalothrin (LD50 = 0.27–0.56 μg a.i./stink bug), with resistance ratios < 2.1-fold. The diagnostic doses of 1.30 (acephate), 0.34 (thiamethoxam), 0.36 (bifenthrin) and 1.73 (lambda-cyhalothrin) μg a.i./stink bug were defined for monitoring the susceptibility of E. heros. In these doses, mortalities of E. heros populations ranged from 55.3% to 100%. Our findings indicate that E. heros presents a lower inter-population variation in susceptibility to acephate, bifenthrin and thiamethoxam than lambda-cyhalothrin, while D. furcatus had similar susceptibility to the insecticides tested. The diagnostic doses defined here will be used in further resistance monitoring programs.