Interaction of starvation and insecticide toxicity in granary weevil Sitophilus granarius L. (Coleoptera: Curculionidae) populations of different susceptibility

摘要

Immediate effects of starvation on granary weevil adults (variants: 25 vessels X 1 individual; 10 X 10) and interactions with toxicity of contact insecticides (dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl and deltamethrin) were tested in laboratory conditions. Effects of starvation were determined in the following weevil populations: laboratory population (normally susceptible to insecticides); a population originating from Cacak; a selected population from Belgrade Port (LD_(95) level: RR 2.3; 4.6; and 15.2 for pirimiphosmethyl, malathion and deltamethrin); one from Bijeljina (LD_(95) level: RR 2.9 and 21.1 for dichlorvos and deltamethrin); and a population obtained from Kikinda (LD_(95) level: RR 2.1; 3.6; 4.1; 5.0; 6.0 and 25.5for pirimiphos-methyl, chlorpyrifos-methyl, cypermethrin, malathion, dichlorvos, and deltamethrin, respectively). Laboratory weevils and those obtained from Belgrade Port and Kikinda were used to determine interaction between starvation and insecticidetoxicity. Insecticide toxicity was determined by exposing surviving individuals to treated filter paper (after previous starvation periods LT_(20) and LT_(50) in the 10 X 10 experiment variant). The mortality percentage for granary weevil adults was modified to include the mortality rate in untreated vessels and the data were processed by probit analysis. According to starvation results, 95 percent mortality was achieved with the laboratory and Kikinda populations (25 X 1 and 10 X 10) after 11 days, while the process took 8 days in the selected population from Belgrade Port and around 8 days (25 X 1) and 10 days (10 X 10) in the Bijeljina population. The data indicate that the established levels of insecticide resistance exerted insignificant effect ongranary weevil susceptibility to starvation. After LT_(20) starvation interval and 24-hr exposure of weevils to treated filter paper, chlorpyrifos-methyl was found to be the most toxic of all tested insecticides, while the least toxic was dichlorvos (LD_(95) level: 14.5 times lower than the leading insecticide). Following LTso starvation and 24-hr exposure to treated filter paper, the most toxic insecticide was dichlorvos and the least toxic deltametlirin (LD_(95) level: 9.6 times lower than dichlorvos). In this starvation variant, dichlorvos increased toxicity 24.9 times at LD_(95) level, while the toxicity increase of deltamethrin was lower. Malathion and deltamethrin demonstrated higher toxicity to unstarved individuals. After LT_(50) starvation ofthe selected weevil adults from Belgrade Port and their 24-hr exposure to treated filter paper, deltamethrin showed higher toxicity than malathion (LD_(95) level: 10.2 times higher), while individuals from Kikinda showed no significant statistical difference in terms of toxjcity. However, compared with the toxicity of the same two insecticides to unstarved adults (both populations), malathion and deltamethrin were found to have identical toxicity. This shows that the resistance levels found in granaryweevil populations from Belgrade Port (selected with LD_(70) pirimiphos methyl) and those from Kikinda had no effect on malathion and deltamethrin toxicity.