Abstract
A toxicity test was conducted in search of a combination of insecticides that is effective against an organophosphorus-resistant strain of housefly. Remarkable potentiation was exhibited when diazinon was paired with carbofuran. The potentiation was greatest when the two compounds were mixed at the ratio of their LD50. However, diazoxon coupled with carbofuran showed little potentiation. Since carbofuran does not inhibit degradation of diazoxon, it seems that diazoxon degradation is not involved in the potentiation between diazinon and carbofuran. When a mixture of diazinon and carbofuran was injected into houseflies, diazinon at a concentration below the LD50 inhibited carbofuran degradation, decreasing the first order rate constant 3.4 times for the carbofuran disappearance. A comparison of the rate of deacylation of acylated acetylcholinesterase produced in vivo by application of a mixture of diazinon and carbofuran and that produced in vitro by diazoxon or carbofuran, showed that the in vivo inhibition of acetylcholinestcrase is mainly caused by carbofuran. From these results, it is reasonable to conclude that the potentiation is attributable to an increase in the internal concentration of carbofuran, which inhibits more acetylcholinesterase, resulting from inhibition of carbofuran degradation by diazinon at sublethal concentrations.
