Resistance Status and Associated Resistance Mechanisms to Certain Insecticides in Rice Weevil Sitophilus oryzae (Coleoptera: Curculionidae)

Abstract

The rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae) was collected from El-Behera governorate (EB). Thefirst generation showed reduced susceptibility to deltamethrin and malathion compared with the laboratory susceptiblestrain (LS). Susceptibility test results (using LS colony as a reference strain) indicated that EB strain has relative toxicityratio, RR50 and RR90 of 16.64 and 9.08 for malathion. Although, EB strain was tolerant to deltamethrin with RR50 of 5.2, itwas marginally resistant to cypermethrin and entirely susceptible to permethrin. The biochemical results showed elevationin the activity of total esterase (ES), carboxylesterase (CE) and glutathione S- transferase (GST) which suggested that themetabolic resistance may has a key function in this population. Furthermore, acetylycholinesterase (AChE) activity in EBstrain was 3.52 times higher compared with LS strain which pointed the insensitivity of AChE in EB strain. Moreover,esterase analysis indicated genetic polymorphism between EB and LS populations which might be attributed to selectionpressure due to continuous exposure to insecticides. This study suggested the existence of malathion and deltamethrinresistance in EB strain which might be a consequence of biochemical alterations. The results of current study indicate theimportance of continuous monitoring of resistance of stored product insect pests to plan successful management strategies.