When either topically applied or mixed in the diet, CME-134, 1-(3, 5-dichloro-2, 4-difluorophenyl)-3-(2, 6-difluorobenzoyl)urea, prevented pupation in last instar larvae of Mamestra. CME-134 was about 5 times as effective as diflubenzuron by topical application, with its LD5D value being 0. 016g/insect. By dietary administration, the LD50 values of both insecticides were almost same (0. 02 ppm) but CME-134 was about twice as effective as diflubenzuron when the LD100 values were compared. After application of the same doses of both CME-134 and diflubenzuron to last instar larvae, chitin synthesis was studied by measuring 14C-GA incorporation into cuticle and midguts. CME-134 inhibited chitin synthesis in vivo. The inhibition by CME-134 progressed faster than by diflubenzuron, although CME-134 was a less potent inhibitor than diflubenzuron for chitin synthesis in vitro using cuticle and midguts. The results suggest that the insecticidal activity of CME-134 is based on strong inhibition of chitin synthesis as so is that of diflubenzuron. CME-134 did not inhibit chitin synthetase that was prepared from the midguts of last instar Mamestra larvae even at a concentration of 1.0x10-4M.
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