Studies on Cyromazine in the House Fly, Musca domestica (Diptera: Muscidae)

Abstract

Cyromazine (CGA72662)(N-cyclopropyl-l,3,5-triazine-2,4-6-triamine) showed excellent growth-inhibiting properties against house fly larvae (Musca domestica L.). It was more effective on early stages of insect development than on later stages. Effect of cyromazine was similar on both susceptible and organophosphorus insecticide-resistant house fly strains, indicating no cross-resistance. Using radioactive cyromazine, we showed that that compound penetrated slowly into house fly larvae. Investigating the mode of action of cyromazine, we observed that cyromazine did not inhibit house fly dihydrofolate reductase in vivo. Neither was inhibition observed in vitro when chicken liver or house fly dihydrofolate reductase were incubated with cyromazine at its maximum water solubility. Because addition of folic acid to the medium did not reverse inhibition of larva growth by cyromazine, it appeared to have no direct effect on folic acid metabolism. Exposure of house fly larvae to cyromazine-treated medium decreased tyrosinase activity in vivo. No inhibition of tyrosinase activity was observed in vitro when the enzyme was incubated with cyromazine at its maximum water solubility, indicating that cyromazine is not a direct tyrosinase inhibitor, but that it or its metabolites may have an effect on biosynthesis of the enzyme. When cyromazine was injected or fed to adult house flies, the parent compound was excreted rapidly and a small amount of cyromazine was metabolized to melamine and excreted.