Determination of Organophosphate Resistance Status and Mechanism in Sitophilus Zeamais Motschulsky (Coleoptera: Curculionidae) From Turkey

Abstract

Objective: The objectives of this study were to determine resistance status to malathion and pirimiphos-methyl insecticides and to make biochemical analysis of resistance mechanism(s) developed to these insecticides in Sitophilus zeamais (S. zeamais) populations, collected from two different locations in Turkey. Two organophosphate insecticides, malathion and pirimiphos-methyl, were examined by bioassay using a discriminating dosage technique with impregnated filter papers. Mortality percentages were determined at the discriminating doses of these insecticides. In addition, esterase, glutathione S-transferase, and cytochrome P450 monooxygenase activities were also determined in this study in order to analyze detoxification mechanism(s) of tested insecticides in S. zeamais. Methods: Bioassay experiments of malathion and pirimiphos-methyl insecticides in S. zeamais populations were performed according to the IRAC susceptibility test method No:006. Furthermore, enzyme activities of esterases, cytochrome P450 monooxygenases, and glutathione S-transferases were determined by using biochemical assays. Results: The bioassay results of malathion and pirimiphos-methyl showed that only Kirikkale population of S. zeamais has resistance to both malathion and pirimiphos-methyl insecticides. However, no resistance was detected to malathion and pirimiphos-methyl insecticides in Samsun population of S. zeamais. Additionally, biochemical analysis displayed that while CYP450-PNOD activities showed an increase only in Kirikkale population (3.0-fold), EST-PNPA activities showed an increase only in Samsun population (1.3-fold). Finally, GST-CDNB activities increased both in Kirikkale (1.4-fold) and Samsun (2.2-fold) populations of S. zeamais compared to susceptible population. Conclusion: Consequently, cytochrome P450 monooxygenases and glutathione S-transferases seem to play a role in organophosphate resistance in Kirikkale population of S. zeamais from Turkey.