A model study integrating time dependent mortality in evaluating insecticides against Bemisia tabaci (Hemiptera: aleyrodidae)

A bioassay and data analysis methodology integrating time –dose dependent mortality in terms of hazard rate of insecticides triazophos and imidacloprid against B. tabaci has been developed. Logrank test had been applied to test the efficacy of the two compounds and corresponding hazard rates computed using product-limit method. LC50 of imidacloprid was observed to be 23.50 ìg/ìl and triazophos was 0.0287 ìg/ìl from the IRAC standard bioassay and the relative toxicity of triazophos was found to be 818.8 fold higher than imidacloprid. The P-values of Logrank test showed that speed of killing at the dosage of 0.05 and 0.1% as well as pooled data of mortality irrespective to the dose of triazophos is significantly higher (p 0.05) than that of imidacloprid. It is concluded that hazard rate or efficacy of the toxicant is dependent on not only dose but also killing speed in terms of time taken to kill. It is clear that deployment of Logrank test with cumulative data of both concentration and time factor has an edge over IRAC method for the toxicity studies on B. tabaci