Cuticle deposition and ecdysteroid titers during embryonic and larval development of the argasid tick Ornithodoros moubata (Murray, 1877, sensu Walton, 1962) (Ixodoidea:Argasidae).

ABSTRACT

Timing of embryonic and larval molts at the ultrastructural level and presence of ecdysteroids (ES) during embryonic and larval development of the argasid tick Ornithodoros moubata were studied. Embryonic "cuticles" A, B, and C were deposited 24-30 hr, 48-56 hr, and 6 days after oviposition, respectively. Deposition of the larval cuticulin layer started on Day 8 of embryonic development and procuticle deposition continued after hatching until apolysis of the larval cuticle 40 hr posthatch. Plaques of cuticulin formed on tips of microvilli 48-56 hr after hatching and procuticle was deposited until after ecdysis. Radioimmunoassay (RIA) was used to determine the ES titer in methanolic extracts of various ages of embryos and larvae. No peaks of RIA-positive material were detected during deposition of envelopes A, B, and C. However two peaks of ES were observed during embryonic development, one which coincided with the shortening of the germ band and a second which coincided with the deposition of the larval epicuticle on Day 8. During larval development, a peak of ES was observed on Day 3 (48-56 hr posthatch) and was correlated with nymphal epicuticle deposition. HPLC-RIA revealed that these last two peaks consisted mainly of 20-hydroxyecdysone together with a small quantity of ecdysone. Conjugated RIA positive material was present in freshly laid eggs and an augmentation of this esterase hydrolysable material was noted at the appearance of each ES peak. Thus the embryos did not appear to be hydrolyzing the maternal apolar conjugates to release ES during embryonic development; on the contrary, they appeared to be conjugating the newly synthesized hormones.