STRUCTURE-ACTIVITY-RELATIONSHIPS OF BENZOYLPHENYL UREAS AS TOXICANTS AND CHITIN SYNTHESIS INHIBITORS IN ONCOPELTUS-FASCIATUS

Diflubenzuron (DFB) acts in milkweed bug, Oncopeltus fasciatus (Dallas), fifth-instar nymphs to reduce their chitin content and survival (topical LD50 = 2.4 μg/g) and slightly prolong their instar duration before molting. With adults from treated fifth-instar nymphs, it also reduces egg production, egg hatchability, and viability of the first-instar nymphs. DFB does not alter in vivo metabolism of α- or β-[3H]ecdysone by fifth-instar nymphs. Isolated abdomens, with their contents removed, from adults 12 hr after emergence convert 14C-labeled glucose, glucosamine, and N-acetylglucosamine to [14C]chitin with yields of 4-5% within 1 hr. [14C]Chitin formation in this in vitro system is inhibited 50% by DFB and polyoxin D at 5.5 × 10-7 and 1.5 × 10-5M or 0.2 and 4.3 μg/g abdominal wall, respectively. A DFB concentration that decreases [14C]chitin formation from N-[14C]acetylglucosamine by 43% results in a 32% accumulation of uridine 5′-diphospho-N-[14C]-acetylglucosamine. Structure-activity studies with 24 benzoylphenyl ureas indicate a good correlation between their toxicity to fifth-instar nymphs and their potency as in vitro inhibitors of postecdysial chitin synthesis. The primary mode of action of benzoylphenyl ureas appears to involve direct and rapid inhibition of chitin synthesis within the integument rather than alterations in levels of extraintegumental hormones. © 1979.