Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 1995
Publication Date: N/A
Interpretive Summary: The utilization of inhibitory analogues of insect hormones to control pest species (i.e. the European corn borer) by interfering with their development and metamorphosis would be an asset to ARS' IPM program. Ecdysiotropins are ideal candidate molecules because they function in stimulating the insect's molting glands to produce precursors to the molting hormone, 20-hydroxyecdysone. The recently discovered low molecular weight ecdysiotropins are small molecules that could be structurally manipulated with relative ease. Our results show that there are significant titer changes in ecdysiotropin levels depending upon the age of the larvae and the diapause (hibernation) state, and that these molecules appear to be released into the insect's blood stream. Results are significant because they support an important physiological role for these ecdysiotropins and provide information as to when they are active in the pest insect. Results would be immediately useful to the scientific community investigating biorational strategies to inhibit larval development in crop pests.
Fluctuations in the titer of low molecular weight ecdysiotropins in proctodaea of nondiapause-bound, diapause-bound, refrigerated diapausing and diapause-break Ostrinia nubilalis were compared. In diapause-bound larvae, ecdysiotropin titers never reached the high levels characteristic of proctodaea from day 3, 4 and OB nondiapause-bound larvae. After 2 weeks of refrigeration, ecdysiotropin levels decreased sharply and then increased gradually through 16 weeks of refrigeration. Upon exposure to diapause-break conditions, ecdysiotropin levels showed significant decreases at 6 h and at 24 h and then increased to their highest levels on day 5 post-diapause-break. When proctodaea were incubated in vitro, low molecular weight ecdysiotropins were released into the medium, however, synthesis was not evident. The nature/concentration of the material released varied with day of the 5th instar and the diapause condition. Our results indicate that the low molecular weight ecdysiotropins function at specific times during larval development and support an important physiological role for these ecdysiotropins.