Mode of Inhibition of Chitin Synthesis by Diflubenzuron in the Cabbage Armyworm, <i>Mamestra brassicae</i> L.

Abstract

No morphological difference was found in the epithelial cells of midgut between the normal and the diflubenzuron-treated last instar larvae of the cabbage armyworm, Mamestra byassicae L. Diflubenzuron and polyoxin D strongly inhibited chitin synthesis in the peritrophic membranes of the midgut when glucosamine or N-acetylglucosamine was applied, as a precursor of chitin, either inside or outside the midgut. When UDP-N-acetylglucosamine was injected into the midgut with polyoxin D, chitin synthesis was blocked, but not with diflubenzuron. The results lead to the following speculation: UDP-N-acetylglucosamine would be formed from glucosamine or N-acetylglucosamine in the epithelial cells and then move to the outer face of the biomembranes of the cells to form chitin. Diflubenzuron may act as an inhibitor of the transport system of UDP-N-acetylglucosamine across biomembranes, since an accumulation of UDP-N-acetylglucosamine is known in insects treated with diflubenzuron. Na+-K+ ATPase and Cat+Mg2+ ATPase were not affected by the insecticide.

Effect of Venom from the Jellyfish Nemopilema nomurai on the Silkworm Bombyx mori L.

“…Jellyfish venom possesses protease activity [ 35 ] but the chitin synthesis was inhibited by SFV. We speculated that SFV may inhibite UDP-GlcNAc transmembrane transport, thus blocking the chitin synthetase and UDP-GlcNAc to synthesize the chitin, according to Mitsui demonstrating that Diflubenzuron inhibited the chitin synthesis of cabbage armyworm [ 36 ].…”

Acute and sublethal toxicity of novaluron, a novel chitin synthesis inhibitor, to Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

“…Chitin is constantly being synthesized in the peritrophic membrane during active stages of the insects life cycle 34. Diflubenzuron has suppressed synthesis of chitin during peritrophic membrane formation in the migratory locust Locusta migratoria L,35 the blowfly Calliphora erythrocephala (Meigen)36 and the cabbage armyworm Mamestra brassicae L 37…”

Chitin synthesis inhibitors: old molecules and new developments

“…Different mechanisms have been proposed to explain how benzoylureas interfere with chitin synthesis. Possible explanations included indirect effects of benzoylureas on the transport of UDP‐GlcNAc transport across membranes (Mitsui et al , 1984), the activities of enzymes involved in chitin degradation and cuticular sclerotization (Ishaaya & Casida, 1974; Ishaaya & Ascher, 1977), and hormonal control of transcriptional activities (Mitlin et al , 1977; DeLoach et al , 1981; Soltani et al , 1984). Studies using insect tissue cultures from imaginal disks and integument epidermis as well as different insect cell lines indicated that benzoylurea compounds inhibit ecdysteroid‐dependent incorporation of GlcNAc into chitin, whereas the uptake of UDP‐GlcNAc was only moderately affected (Mikolajczyk et al , 1994; Oberlander & Silhacek, 1998).…”