Correlations between ecdysteroid titers and integument structure in nymphs of the tick, Amblyomma hebraeum Koch (Acarina: Ixodidae)

Abstract

The temporal correlation between the ecdysteroid titer and the structure of the extensible integument was studied during the development of nymphs to adults in the ixodid tick Amblyomma hebraeum Koch.Using a radioimmunoassay (RIA) only small hormone concentrations were found in hemolymph and in whole ticks during the first 17 days after begin of feeding.During this phase, much new endocuticle was deposited and the mitotic period initiated.After the 17th day the ecdysteroid titer increased to a maximum at day 23 (about 14 ng ecdysterone equivalents per tick).During this phase the mitotic period ended, apolysis was initiated, and the tick began to deposit the epicuticle (day 23).Thereafter the titer dropped to low values around ecdysis (day 31-34; about y 2 ng per tick).During this time the epicuticle (day 23-25) and the exocuticle (day 25-ecdysis) were deposited and the nymphal cuticle digested.Chemical analysis by high performance liquid chromatography and RIA showed the presence of ecdysone and mainly ecdysterone.