Insecticide metabolism and partition in isolated organs of house fly larvae and adults

Abstract

Isolated organs of larvae and adults of house flies were incubated in nutrient solutions to study uptake and metabolism of insecticides. Single organs were incubated in solutions of radiolabeled paraoxon, methyl-paraoxon, parathion, and tetrachlorvinphos. Larval fatbody, consisting of a single layer of large cells, was studied most extensively. Uptake and release of the insecticides led to the same partition between solution and organ. This was not so in adult gut or abdominal body wall. Partition between fatbody and solution was 2250, 370, and 11 for parathion, tetrachlorvinphos, and paraoxon, respectively. Release of insecticide into the medium followed first-order kinetics. Rate of equilibration was slowest for tetrachlorvinphos (half value time 17 min). Parathion exchanged faster and paraoxon fastest (half value < 1 min). Metabolism was mainly studied in two strains Fc and Nic with polysubstrate monooxygenases causing resistance to paraoxon and other insecticides, and in a tetrachlorvinphos resistant strain CH with high GSH 2S-transferase activity. Oxygenase activity varied widely between individual larvae, the variation being at least partly genetic. Sesamex and parathion inhibited paraoxon metabolism. Transferase activity in fatbodies of CH was maximally 8 nmol tetrachlorvinphos/hour, whereas larvae in vitro had an activity of 52 nmol/hour. Incubation of isolated organs is well stuited for genetic studies on detoxication capacity since it enables the study of metabolism in individual small insects. Its merits and limitations for toxicological analysis are discussed.