Effectiveness of wheat-applied contact insecticides against Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Abstract: The effectiveness of several contact insecticides: malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin+piperonyl butoxide (PBO) synergist, bifenthrin, thiamethoxam, spinosad and abamectin against a laboratory population of Sitophilus oryzae in treated wheat, was examined. Adult mortality was determined after 2, 7 and 14 days of exposure, while minimum effective doses (MED) were determined based on F1 and F2 offspring production after 8 and 14 weeks, respectively. Chlorpyrifos-methyl (LD50 = 0.36 mg/kg) and pirimiphos-methyl (LD50 = 0.43 mg/kg) were the most effective contact insecticides after 2 days of exposure, while abamectin was the least effective (LD50 = 23.53 mg/kg). Chlorpyrifos-methyl (LD50 = 0.13 mg/kg) had the highest effectiveness after 7 days of exposure, and malation the lowest (LD50 = 1.26 mg/kg), while abamectin (LD50 = 0.07 mg/kg) was the most effective insecticide after 14 days, and malathion the least (LD50 = 1.11 mg/kg). Chlorpyrifos-methyl and deltamethrin had the lowest MEDs (> 0.5 and 0.6 mg/kg, respectively) in F1 generation, and deltamethrin and bifenthrin (0.4 and 0.5 mg/kg, respectively) in F2 generation, while spinosad showed the highest MED both in F1 and F2 with > 20 and 10 mg/kg, respectively.