Abstract: The changes of ecdysteroid (20-E) in the whole body and cuticulogenesis during nymphal stage were studied by HPLC and RIA, and SEM respectively. 20-E existed in all the nymphal stages. Its level was low in nymphs unfed, feeding and during the first 4 days after engorgement (0.71～1.30ng/nymph). Then it began to increase sharply on the 6th day after engorgement when apolysis was initiated and exuvial space appeared. 20-E reached its peak (8.70 ng/nymph) during the deposition of the new epicuticle on the 8th day after engorgement. Thereafter, 20-E dropped to low value again. The procuticle deposition and old cuticle digestion occurred during this period. There results demonstrated that the highest concentration and sharp increase of 20-E were coincident with the deposition of new epicuticle and the formation of exuvial space (apolysis) separately. No relationship was observed between 20-E concentration and new procuticle synthesis.

Key words: Haemaphysalis longicornis, nymph, 20-hydroxyecdysone, cuticulogenesis