Studies on the action mechanism of benzoylurea insecticides to inhibit the process of chitin synthesis in insects: A review on the status of research activities in the past, the present and the future prospects

In this review an effort was made to summarize the up to date information on the knowledge on the action mechanism of diflubenzuron (DFB), a prototype chemical for the benzoylurea type insecticides, with respect to its molecular mechanism to inhibit insect chitin synthesis. The key problem in pinpointing the action site of this insecticide has been the lack of in vitro demonstration of its action to inhibit insect chitin synthesis under cell free conditions. This problem was solved when an approach using a intracellular vesicle preparation from the cuticle of newly molted Periplaneta americana was developed. Using this approach it has become possible to identify that DFB indeed inhibits the process of incorporation of N-acetylglucosamine into insect chitin. Recently there has been a breakthrough in this field, when a sulfonylurea receptor (SUR) was identified in Drosophila melanogaster. This information was instrumental in establishing that insect SUR in the above intracellular vesicular preparation from P. americana as well as Blattella germanica is likely the actual target site of DFB to cause inhibition of chitin synthesis. The role of SUR in this case has been determined, by using glibenclamide, a typical SUR specific inhibitor as an aid, to be helping the exocytotic movement of these vesicles as is the case of other members of the group of ABC-transporters to which insect SUR belongs. In this case both DFB and glibenclamide have been shown to cause the depolarization of the vesicle membrane through inhibition of the K+ channel, which leads to their inhibition of chitin synthesis.