Correlation between ecdysteroids and cuticulogenesis in nymphs of the tick Ornithodoros parkeri (Acari: Argasidae).

Ecdysteroids and cuticulogenesis were studied in third-instar nymphs of the tick Ornithodoros parkeri Cooley. Ecdysteroid titer increases slightly during the postfeeding intermolt period, which correlates with the deposition of additional procuticle lamellae. The titer increases at the time of apolysis, peaks at the time of epicuticle deposition, and then drops to a low but detectable level from the time of procuticle deposition until after ecdysis. Ecdysone and 20-hydroxyecdysone are the two major ecdysteroids present during the postfeeding intermolt period and the period of epicuticle deposition. After ecdysis, the ecdysteroid immunoreactive material is composed principally of an unknown compound more polar than 20,26-dihydroxyecdysone and is found only in the midgut. This compound is possibly a metabolite of ecdysteroids left over from the previous instar.