Dietary TH 6040 alters composition and enzyme activity of housefly larval cuticle

Housefly larvae of 2 days of age were allowed to grow in media containing 0, 0.4, 1.0, or 2.5 ppm TH 60401-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea] for 3 days prior to analysis of the cuticle for structural components (chitin and protein) or enzymes important in cuticle formation (chitinase and phenoloxidase). As the TH 6040 concentration is increased, the amount of chitin is progressively reduced such that, at 2.5 ppm TH 6040, the level is only 25% of normal. The amount of cuticle protein is unaffected so the protein: chitin ratio increases from 3.4 in the control larvae to 14.3 in 2.5 ppm-treated larvae, an alteration which probably affects the elasticity and firmness of the endocuticle. Dietary TH 6040 at 1.0 ppm increases the cuticle chitinase activity to about 180% and the cuticle phenoloxidase activity to 155% as compared with control larvae, with a further chitinase activity increase to 240% of normal at 2.5 ppm TH 6040. These enzyme changes are expected to hamper the build-up or maintenance of the cuticle chitin and enhance sclerotization of the exocuticle.