Control failure and insecticides resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia

Abstract

The lesser grain borer Rhyzopertha dominica is a serious pest that causes significant economic damages in stored grains. The presence of this pest is mainly controlled using a small number of insecticides increasing risks of compromising the control efficacy due to the selection of resistant populations. Here, the control failure and potential resistance to pyrethroid and organophosphate insecticides frequently used for the control of R. dominica in Colombia were assessed. Concentration–mortality bioassays with synergized and unsynergized insecticides were used to assess potential metabolic-based pyrethroids resistance mechanisms. Based on the field recommended doses, the results revealed that while the pirimiphos-methyl is still efficient against R. dominica, both type I (i.e., bifenthrin) and type II (i.e., deltamethrin) pyrethroids presented control failure and their insecticidal activity was compromised. Although no differences in susceptibilities between the populations were found for the bifenthrin insecticide, the LC50s of Ibagué (1.83 μl/gr of grains) and El Espinal (1.67 μl/gr of grains) populations were higher than the recommended rate. Furthermore, significant differences in susceptibility to deltamethrin resulted in resistance ratios RR50 > 32-fold and RR95 > 188-fold between the least (El Espinal) and the most (Ibagué) susceptible populations. Moreover, when synergized, the toxicity of deltamethrin was enhanced but resistance ratios kept at high levels (RR50 > 11-fold and RR95 > 40-fold) indicating possible existence of simultaneous metabolic and altered action-site mechanisms of resistance to pyrethroids in Colombian populations. Our results highlight the urgent need for nationwide monitoring of insecticides control failure and resistance in stored pests for better management schemes.