COMPARISON OF BIOCHEMICAL AND BIOASSAY METHODS IN ASSESSING ORGANOPHOSPHATE RESISTANCE IN BLATTELLA GERMANICA

In this study we employed two methods for gauging the sensitivity of B. germanica strains to organophosphorus insecticides: an in-vivo bioassay that used linear regression analysis (with mortality on a probit scale and logarithm of concentration) and an in-vitro enzyme assay.In the bioassay method, B. germanica nymphs of stage 1 (2-3 days old) were exposed to patches of paper impregnated with 2% diazinon and propoxur. Compared to the sensitive (reference) strains, all but one of the tested strains showed resistance to diazinonzinon with resistance ratios of 0.97 to 1.67. As for propoxur, all strains were sensitive with the exception of one subject that showed a resistance ratio of 1.6. The enzyme assays used common esterase and acetylcholine esterase methods. Comparison of in-vivo and in-vitro tests on stage 1 nymphs of B. germanica shows that both methods are reasonably sensitive in measuring resistance/sensitivity ratios. In addition, the bioassay modality makes it possible to gauge the degree of insecticide sensitivity while the in-vitro method can only determine quantitative or qualitative changes in enzymes effected by carbamates and organophosphates. This study is the first of its kind, conducted by the school of Public Health in Tehran University of Medical Sciences.