Abstract
The novel ingestion bioassay method was developed for detecting and monitoring resistance of Euschistus heros 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 E. heros 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 E. heros populations. In order to monitor the susceptibility of E. heros 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 E. heros 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.
Highlights
The Neotropical brown stink bug Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) is currently one of the major pests of soybeans (Glycine max (Merril)) in Brazil, causing significant and often irreversible damage to crops [1,2,3]
Insecticide sprays for the control of phytophagous brown stink bugs have been frequently used, including insecticides belonging to three chemical groups, which can be used alone or in formulated mixtures [16]
The limited availability of insecticides and frequent use of the same mode of action may favor the selection of resistant populations, especially if insect resistance management strategies (IRM) are neglected [17,18,19]
Summary
The Neotropical brown stink bug Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) is currently one of the major pests of soybeans (Glycine max (Merril)) in Brazil, causing significant and often irreversible damage to crops [1,2,3]. The damage caused by this species results from the insertion of the stylet in the soybean plants or pods, wherein they inject salivary secretions facilitating the feeding process. They can promote the development of fungal diseases and cause physiological disorders, such as leaf retention, compromising yields by up to 30% if they feed on pods throughout their reproductive stages [4,5,6,7,8,9]. Overall pest control in soybean is practically based on the use of chemicals for insects and mites as well as for weeds and diseases affecting the crop [12,13]. The application of many of these insecticides has not achieved the desired control efficiency, and the high number of applications has not reduced the population increase of E. heros in different crops [10,11,14]
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