Further evidence that diapause in the gypsy moth, Lymantria dispar, is regulated by ecdysteroids: A comparison of diapause and nondiapause strains

A nondiapause strain of the gypsy moth offers an additional tool for evaluating the regulation of diapause in this species. Patterns of protein expression in the gut and gut enzyme activity distinguished the two strains. Synthesis of a 55 kDa gut protein, previously linked to diapause, began 14 days after oviposition in both the diapause (D) and nondiapause (ND) strains. Though synthesis of this protein persisted in the D strain, its synthesis decreased after day 18 in the ND strain. In the D strain, activity of the proteolytic enzymes (trypsin, chymotrypsin, elastase, aminopeptidase) and esterase remained low, while activity of all of these enzymes increased dramatically in the ND strain 18-20 days after oviposition. By contrast, alkaline phosphatase (ALP) activity was high in both strains 15-17 days after oviposition, activity remained high in the D strain but in the ND strain activity then decreased. Patterns of ALP zymograms were similar in the two strains on day 15, but later a band of high mobility appeared only in the D strain. When 20-hydroxyecdysone was added to hanging drop cultures containing ND pharate larvae 15 days after oviposition, the larvae assumed the characteristics of diapause larvae: the 55 kDa gut protein was synthesized, the ALP zymogram revealed the characteristic diapause pattern, and they failed to ingest culture medium. The fact that 20-hydroxyecdysone could elicit these responses in ND individuals further supports previous results indicating that ecdysteroids promote the induction and maintenance of the pharate larval diapause in this species.