AGE-SPECIFIC EFFECTS OF A NONSTEROIDAL ECDYSTEROID AGONIST, RH-5992, ON THE SPRUCE BUDWORM, CHORISTONEURA-FUMIFERANA (LEPIDOPTERA, TORTRICIDAE)

The non-steroidal ecdysone agonist, RH-5992, is effective in inducing an incomplete molt in the spruce budworm, Choristoneura fumiferana (Cl emens), only when it is fed to the larvae prior to the appearance of t he endogenous ecdysteroid peak. When this compound is administered aft er the ecdysteroid peak, the larvae molt normally into the next stage. However, because of its persistence, the agonist induces an incomplet e molt in the subsequent larval stage. The effect does not appear to b e due to ecdysone responsive tissues becoming refractory after the ecd ysteroid peak. Choristoneura hormone receptor 3 (CHR3), a homologue of Manduca hormone receptor 3 (MHR3), is induced in the epidermis, fat b ody and midgut of 6th instar larvae treated with RH-5992 during all da ys of the 6th stadium. Possible reasons for this age specific effect a re discussed.