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Title: IN VIVO AND IN VITRO EFFECTS OF TEBUFENOZIDE AND 20-HYDROXYECDYSONE ON CHITIN SYNTHESIS

Author
item SMAGGHE, G - UNIV. OF GENT, BELGIUM
item Gelman, Dale
item TIRRY, L - UNIV. OF GENT, BELGIUM

Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tebufenozide (RH5992) belongs to a class of compounds (dibenzoylhydrazines) which is a candidate pesticide for controlling lepidopteran pest species. A nonsteroidal, molting hormone agonist, RH5992 interferes with insect development and molting. The effects of RH5992 on chitin (major structural component of insect cuticle) synthesis and cuticle production remain to be elucidated. Here we report that in the European corn borer and beet armyworm, in addition to causing the premature initiation of molting, RH5992 induces chitin synthesis. However, at the doses used, the cuticle formed is abnormal and pupal formation as well as adult development and emergence are inhibited. When chitin is being actively snythesized, RH5992 inhibits additional chitin production. These insect-specific effects probably are due to the ability of RH5992 to mimic the action of molting hormone as well as to the inability of the insect to inactivate/metabolize RH5992. Results clarify the mechanism of action of RH5992 in causing abnormal insect development, abnormal cuticle production and in inhibiting molting. Information generated should be useful to other scientists investigating the role of molting hormone in new cuticle production as well as to scientists developing strategies for using RH5992 in the field to control lepidopteran pests.

Technical Abstract: Last-instar larvae of the beet armyworm, Spodoptera exigua (Hubner) fed on diet containing tebufenozide exhibited a premature induction of chitin synthesis. Treatment with tebufenozide also resulted in the precocious induction of larval moulting (apolysis. Subsequently, normal ecdysis was inhibited and treated larvae died while still within their old cuticle. In other experiments 1-day- old pupae of the European corn borer, Ostrinia nubilalis, (Hubner) were injected with various doses of tebufenozide or 20E. Incorporation of [14C]GlcNAc served as a measure of chitin production and was monitored in cultured day-4 and day-5 claspers. Tebufenozide at 100,200, and 400 ng induced synthesis in day-4 claspers where incorporation was enhanced 8-fold. A similar stimulation of chitin synthesis was observed with 2000 ng of 20E. For day-5 claspers, high doses of tebufenozide inhibited chitin synthesis. Treatment with tebufenozide had a deleterious effect on adult development and on adult emergence. Even at the lowest dose injected, 10 ng, adult eclosion was completely inhibited. Our results indicate that in both larvae and pupae/pharate adults, tebufenozide can induce the premature synthesis of chitin as can 20E, but the effective dose of tebufenozide is much lower than that for 20E. Results support the view that tebufenozide, although nonsteroidal in nature, is able to mimic the activity of ecdysteroids in inducing chitin synthesis. However, development in treated insects is abnormal and the newly formed cuticle is imperfect and unable to survive a moult.