Ecdysone metabolism by soluble enzymes from three species of diptera and its inhibition by the insect growth regulator TH-6040

Homogenates of larvae, pupae, and adults of house flies (Musca domestica L.), flesh flies (Sarcophaga bullata Parker), and blow flies (Phormia regina (Meigen)) have been examined for enzymes which convert α- and β-ecdysone to apolar products. Most of the activity was found in the soluble fraction from house flies and flesh flies but none of the blow fly fractions was active. Two enzymes seem to be involved in the ecdysone metabolism, one requiring NADPH and the other functioning without this cofactor. The product of the latter enzyme is thought to be the 3-dehydro-ecdysone. This product is further converted to the 3α-hydroxy isomer of ecdysone by the NADPH-requiring enzyme. On feeding the insect growth regulator TH-6040 (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea) to larvae at dietary levels ranging from 0.3 to 10 ppm, the activity of the enzyme producing the 3-dehydro product is reduced by 20 to 82%. It is suggested that the growth regulator exerts its effect on pupal-adult ecdysis through its inhibition of ecdysone metabolism.