Synergistic effects of chlorpyrifos with piperonyl butoxide (pbo) against the lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

Objective: To investigate the co-toxicity and co-efficient activity of Chlorpyrifos (Dursban 20EC), an organophosphate and Piperonyl butoxide (PBO) against the lesser meal worm Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) (A. diaperinus).Methods: The repellent activity was carried out by the residual film assay technique. Statistically the dose mortality relationship was expressed as a median lethal dose (LD50) by the probit analysis. The regression lines and isoboles were drawn using the Fig-P (Biosoft) package.Results: The Co-efficient values showed that all ratios of chlorpyrifos and piperonyl butoxide offered synergistic action to both larvae and adult. We observed that the toxicity of the chlorpyrifos was decreased as the ratio (amount) of PBO was increased. The individual LD50 value of chlorpyrifos for adult is 0.1241 µg/cm2. But in the mixture, the share of chlorpyrifos are 0.0298, 0.0366, 0.0246 and 0.0108 µg/cm2 at ratios of 1:1, 1:3, 1:5, 1:10 when PBO causes reduction of dose level of 75.84%, 70.53 %, 80.19% and 91.30% respectively. In case of larvae the individual LD50 value of chlorpyrifos is 0.2943 µg/cm2. But in the mixture, the share of chlorpyrifos are 0.05, 0.019, 0.015 and 0.010 µg/cm at ratios of 1:1, 1:3, 1:5;1:10 when PBO causes reduction of dose level of 80.01%, 93.54%, 94.90% and 96.60% respectively.Conclusions: The study suggests that the mortality rate of lesser meal worm is increase with the increase of insecticide dose. The LD50 values of the insecticides are inversely related to the toxicity of the insecticides i.e. higher the LD50 value lower the toxicity of the insecticide