Inhibition of Chitin Synthesis by Diflubenzuron in Mamestra brassicae L.

Abstract

Diflubenzuron was found to inhibit chitinous cuticle formation in Mamestra in vivo. When epidermis from last instar larvae was cultured in vitro in the presence of diflubenzuron or polyoxin D, both compounds inhibited chitin synthesis with I₅₀ of 8.9×10^-9M for diflubenzuron and 8.8×10^-8M for polyoxin D. When larvae were injected with ¹⁴C-GA after treatment of diflubenzuron, ¹⁴C-UDP-AGA was found to accumulate in vivo. Apparently diflubenzuron blocks the terminal polymerization step in chitin synthesis. Chitin synthetase activity in cell-free extracts was inhibited by polyoxin D but not by diflubenzuron. Yet the enzyme preparations from the animals treated with diflubenzuron were about one-tenth as active as those from the controls.