Ultrastructural effects of a non-steroidal ecdysone agonist, RH-5992, on the sixth instar larva of the spruce budworm, Choristoneura fumiferana

A. Retnakaran, A. MacDonald, W. L. Tomkins, C. N. Davis, A. J. Brownwright, S. R. Palli

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42 Scopus citations


Force feeding of RH-5992 (Tebufenozide), a non-steroidal ecdysone agonist to newly moulted sixth instar larvae of the spruce budworm, Choristoneura fumiferana, (Lepidoptera: Tortricidae) initiates a precocious, incomplete moult. Within 6 h post treatment (pt) the larva stops feeding and remains quiescent. Around 12 h pt, the head capsule slips partially revealing an untanned new head capsule that appears wrinkled and poorly formed. By 24 h pt, the head capsule slippage is pronounced and there is a mid-dorsal split of the old cuticle in the thoracic region but there is no ecdysis. The larva remains moribund in this state and ultimately dies of starvation and desiccation. The temporal sequence of the external and internal changes of the integument were studied using both scanning and transmission electron microscopy. Within 3 h pt, there is hypertrophy of the Golgi complex indicating synthetic activity and soon after, large, putative ecdysial droplets are seen. Within 24 h, a new cuticle that lacks the endocuticular lamellae is formed. The formation of the various cuticular components, the degradation of the old cuticle and changes in the organelles of the epidermal cells of the mesothoracic tergite are described. The difference between the natural moult and the one induced by RH-5992 are explained on the basis of molecular events that take place during the moulting cycle. The persistence of this ecdysone agonist in the tissues permits the expression of all the genes that are up-regulated by the presence of the natural hormone but those that are turned on in the absence of the hormone are not expressed.

Original languageEnglish
Pages (from-to)55-68
Number of pages14
JournalJournal of Insect Physiology
Issue number1
StatePublished - Feb 19 1997

Bibliographical note

Funding Information:
The gift of RH-5992 by Rohm and Haas Co. is gratefully acknowledged. This study was supported by the Canadian Forest Service and a grant from Rohm and Haas Co., Spring House, PA, USA. We thank Dr S. S. Sohi and Mrs K. Jamieson for critical comments on the manuscript.


  • Dibenzoyl hydrazine
  • Ecdysone agonist
  • Ecdysteroids
  • Gene regulation
  • Moult induction
  • RH-5992
  • Scanning electron microscopy Transmission electron microscopy
  • Spruce budworm
  • Tebufenozide

ASJC Scopus subject areas

  • Physiology
  • Insect Science


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