A ROLE FOR ECDYSTEROIDS IN THE INDUCTION AND MAINTENANCE OF THE PHARATE FIRST INSTAR DIAPAUSE OF THE GYPSY-MOTH, LYMANTRIA-DISPAR

Several lines of evidence suggest a novel regulatory mechanism for dia pause regulation in the gypsy moth. We propose that ecdysteroids play a role in the induction and maintenance of the pharate first instar la rval diapause in this species, A 55 kDa gut protein that is indicative of diapause is expressed in intact and neck-ligated pharate larvae bu t is not expressed when a ligature is placed posterior to the prothora x, site of the prothoracic gland, Guts cultured in vitro for 12 h ceas e to synthesize the 55 kDa protein, but synthesis of the protein resum es if the culture medium is enriched with a prothorax extract from pha rate larvae or a prothoracic gland extract from fifth instar larvae, I njection of 20-hydroxyecdysone or the ecdysteroid agonist, RH-5992, in to isolated abdomens stimulates synthesis of the diapause-specific 55 kDa protein, suggesting that the essential factor from the prothorax i s an ecdysteroid, KK-42, an imidazole derivative known to inhibit ecdy steroid biosynthesis, averts diapause when applied to prediapausing ph arate first instar larvae, but this effect can be countered by applica tion of 20-hydroxyecdysone or RH-5992, i.e. KK-42 treated pharate larv ae that are exposed to an ecdysteroid or RH-5992 readily enter diapaus e, A chilling period (120 days at 5 degrees C) is normally adequate to prompt an immediate termination of diapause when pharate larvae are t ransferred to 25 degrees C, but if such larvae are held in hanging dro p cultures with ecdysteroids they fail to terminate diapause, Together , these results suggest that ecdysteroids are essential for the induct ion and maintenance of diapause and imply that a drop in the ecdystero id titer is essential for diapause termination. (C) 1997 Elsevier Scie nce Ltd.