Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2001
Publication Date: N/A
Citation: Interpretive Summary: Insecticide penetration into insects is crucial to its efficacy. Synergists, nontoxic chemicals that inhibit detoxification, are used extensively in over-the-counter insecticide formulations to increase their efficacy against insecticide resistant insects. However, occasionally addition of synergists produces undesired effects, such as reduced penetration of pesticide through the cuticle. Scientists at the Center for Medical, Agricultural and Veterinary Entomology and University of Florida in Gainesville, Florida, have examined the effects of synergist use on propoxur cuticular penetration rates in the German cockroach. They have found that propoxur entering the cockroach is significantly reduced in the presence of two widely used insecticide synergists. These data will aid the development of better insecticide combinations and formulations.
Technical Abstract: Effects of the synergists piperonyl butoxide (PBO) and S,S,S tributyl phosphorotrithioate (DEF) on propoxur pharmacokinetics were examined in the German cockroach, Blattella germanica (L.). Treatment of adult male German cockroaches with the cytochrome P450 monooxygenase inhibitor, PBO, or the esterase inhibitor, DEF, increased propoxur toxicity by 2 and 6.8 fold, respectively, implicating hydrolysis as a major detoxification route of propoxur in the German cockroach. However, significant hydrolytic metabolism could not be demonstrated conclusively in vitro resulting in a conflict between in situ bioassay data and in vitro metabolic studies. In vitro propoxur metabolism with NADPH fortified microsomes produced at least 9 metabolites. Formation of metabolites was NADPH dependent; no quantifiable metabolism was detected with cytosolic fractions. However, microsomal fractions lacking an NADPH source did produce a low, but detectable, quantity of metabolites (1.6 pmol). PBO inhibited NADPH dependent propoxur metabolism in a dose dependent fashion, implicating cytochrome P450 monooxygenases as the enzyme system responsible for the metabolism. Interestingly, DEF also inhibited the NADPH dependent metabolism of propoxur, albeit to a lower extent. Treatment with PBO or DEF also caused a significant reduction in the cuticular penetration rate of propoxur. The data demonstrate that unanticipated effects are possible with synergists and that caution must be exercised when interpreting synergist results.