Why does identification matter? Thrips species (Thysanoptera: Thripidae) found in soybean in southern Brazil show great geographical and interspecific variation in susceptibility to insecticides

Abstract

Thrips have historically been considered secondary soybean pests in Brazil and neighboring countries. However, since the 2010s they have gained importance in soybean in central and northern Brazil. From 2017 onwards, high infestations of thrips have also been detected in soybean in southern Brazil. Here, we collected and identified thrips species from soybean fields in southern Brazil throughout the 2022/2023 season and conducted laboratory bioassays to assess their susceptibility to selected insecticides. Thrips were exposed to the field concentrations of selected insecticides in leaf-dip bioassays using soybean leaves. Our results indicated that Frankliniella schultzei (Trybom, 1910) and Caliothrips phaseoli (Hood, 1912) are the major thrips species found in soybean in southern Brazil. These species exhibited high mortality and relatively low geographic and interspecific variation in susceptibility to the field concentrations of spinetoram, methomyl, spinetoram + methoxyfenozide and profenofos + cypermethrin. In general, most populations of C. phaseoli were more susceptible to acephate, chlorfenapyr and abamectin than F. schultzei, whereas bifenthrin + carbosulfan showed high lethality against most populations of F. schultzei, however, both species had wide geographic variation in susceptibility to these chemistries. In contrast, populations of both species have low mortality when exposed to the field concentrations of imidacloprid, lambda-cyhalothrin and lambda-cyhalothrin + sulfoxaflor. In summary, our study documents significant variations in the susceptibility of F. schultzei and C. phaseoli to selected insecticides, both among species and among geographical areas across southern Brazil. These results highlight the importance of species identification for the effective control of thrips in soybean in Brazil and other South American countries.