Insecticide synergism by chlordimeform : nature and mechanism(s) of action

Abstract

The nature of insecticide synergism by chlordimeform (CDF) was studied with emphasis on the biochemical mechanism by which this interaction could be achieved. Insects used in these studies were the tobacco budworm, Heliothis virescens (F.), and the house fly, Musca domestica (L.). Three enzyme systems commonly involved in the detoxification of insecticides were tested for inhibition by CDF. Rates of absorption and excretion of 4 labeled insecticides were tested for effects by CDF. Two experiments were designed to provide evidence on the mode of action of CDF. Insects with known resistance mechanisms were examined for cross resistance to CDF. The target enzyme, acetylcholinesterase (AChE), for organophosphates and carbamates was also tested to find if CDF affected it. The methods available for analyzing synergism were reviewed. A revised method, based on those available, is proposed and critiqued. This procedure incorporates provisions for various combinations of compounds, depending on the relative toxicity of each. It also provides a means to test for significant differences between the theoretical dosage-mortality line calculated on the assumption that the compounds are additive and the dosage-mortality line that was observed. Two of the 3 tested enzyme systems were affected by CDF. CDF proved to be an inhibitor of parathion metabolism by microsomes from house flies. Glutathione dependent transferases were 50% inhibited by 3 x 10^-4 M CDF. The ali-esterases showed no indication of inhibition with 10^-2 M CDF. Rates of absorption were tested by topically applying labeled insecticide to H. virescens larvae. Larvae exposed for 24 hours to CDF had a decreased rate of absorption of carbaryl, DDT and aldrin compared with control larvae. There were no significant differences in the rate of absorption of parathion. Rates of metabolism and excretion by H. virescens larvae were tested by injecting 4 labeled insecticides. Parathion and carbaryl were excreted at slower rates by larvae exposed for 24 hours to CDF than control larvae. However, CDF did not affect the rate of excretion when DDT or aldrin were tested...