Evaluation of synergism/antagonism in the toxicity of pyriproxifen against cotton mealybug through co-administration with silicon dioxide under laboratory conditions

Silicon dioxide damages the protective waxy layer of insect body and insects die due to desiccation. But due its slow action and effectiveness at high dose, its combination with different insecticides is recommended. The present study was carried out to evaluate synergistic/antagonistic effects of silicon dioxide on the toxicity of pyriproxifen against cotton mealy bug under laboratory conditions. Twenty different dose ratios between pyriproxifen and silicon dioxide ranging from 1:0.0025 to 1:3 were evaluated against adult female and egg sac stages. Two controls (one with pyriproxifen and 2nd without any treatment) were arranged for comparison purpose. The results revealed that intensity of synergistic effect on the toxicity of pyriproxifen increased with increasing concentrations of silicon dioxide. The treatments, having silicon dioxide admixed with pyriproxifen, removed many fold wax from the body of adult female than the treatments having only pyriproxifen. Approximately, 1.3 and 1.8 times greater mortality was exhibited after 1 and 2 days exposure interval than that of control, where no silicon dioxide was mixed with pyriproxifen. Similarly, 14 and 9.1 times greater wax was removed and 9.1 times greater weight loss was exhibited over control. Maximum mortality (92.5%) of nymphs at ovisac stage of mealybug was recorded, when it was exposed to ratio 1:3 and was found approximately 1.5 times greater than that of control (62.4%), where no silicon dioxide was mixed with pyriproxifen. Minimum mortality (67.5%) was observed, when it was exposed to the ratio of 1:0.0025. After a post treatment interval of 2 days, maximum mortality (94.2%) of nymphs at egg-sac stage of mealybug was observed, when it was exposed to ratio 1:3 and was at least 1.6 times greater than control (60.1%), where no silicon dioxide. The better ratio was 1:0.05 to 1:3.0. In future, silicone dioxide would be a synergist for pyriproxifen against mealybugs.