Combined effects of contact insecticides and 50 °C temperature on Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in wheat grain

The effects of the insecticides deltamethrin, bifenthrin, thiamethoxam, spinosad and abamectin were tested in the laboratory in combination with extreme temperature of 50 degrees C to discover potential improvements of existing pest management programmes for Sitophilus oryzae (L.) control. Adults were released into wheat grain treated with three insecticide doses ranging 0.125-1.0 mg/kg and exposed to 50 +/- 1 degrees C temperature at the intervals of 0, 65, 75 and 85 min, and direct and combined effects were determined after 1, 2, 7 and 14 days of exposure/recovery at 25 +/- 1 degrees C and 60 +/- 5% r.h., as well as impact on F-1 progeny production/reduction PR (%) after 8 weeks. The results showed that the mortality of S. oryzae adults increased with exposure/recovery duration more than under the activity of each insecticide alone and its interaction with extreme temperature. After 14 days, all three rates of deltamethrin (0.125-0.5 mg/kg), the two higher rates of bifenthrin (0.25 and 0.5 mg/kg) and the highest rates of abamectin (0.5 mg/kg) and thiamethoxarn (1.0 mg/kg) caused maximum adult mortality (100%) and PR (100%) after weevil exposure to 50 C already after the interval of 65 min, while spinosad had the same effect after 75 and 85 min, which effectiveness was 1.25-20 times higher than the activities of the insecticides and 50 degrees C temperature alone, considering all trial variants. The lowest rate of bifenthrin (0.125 mg/kg) was found after 65 min activity in combination with exposure to 50 degrees C, and especially spinosad (0.25 mg/kg) after 65 and 75 min, to have stimulated progeny production 17, 33 and 236%, respectively, while deltametrin showed 100% effectiveness against S. oryzae in all combinations of wheat grain treatment at 50 degrees C temperature, including the dose 0.125 mg/kg. (C) 2016 Elsevier Ltd. All rights reserved.