EVOLUTION OF ECDYSTEROIDS AND OF THEIR APOLAR CONJUGATES DURING THE POSTEMBRYONIC DEVELOPMENT OF THE TICK ORNITHODOROS-MOUBATA

The ecdysteroid (ES) content of the soft tick Ornithodoros moubata was investigated during the five successive nymphal molting cycles by mea ns of an enzyme immunoassay (EIA). Samples were submitted to esterase hydrolysis in order to release free ecdysteroids from the acyl-ester c onjugates (AP = apolar products). Crude and hydrolysed extracts were t hen analyzed by EIA using two different antibodies, a monoclonal raise d against 20-hydroxyecdysone (20E) and a polyclonal raised against ecd ysone (E). With the crude extracts, each molting cycle was associated with an ES peak, occurring in the middle of the instar. 20E was prepon derant during the first 2 nymph cycles, but the proportion of E and ot her ES increased during the following instars. The shape of the peak a lso seemed to be different. Hydrolysis with esterase revealed that the total immunoreactivity was increased by 10- to 20-fold as compared to crude extracts in N1, N2, and N3, then by approximately 50- and 80-fo ld in N4 and N5 (last instar), respectively. The use of both antibodie s and of HPLC fractionation showed that not only 20E was conjugated as AP, but also two other ES tentatively identified as ecdysone and 2-de oxyecdysone. It is suspected that a conversion of conjugated 20E to le ss immunoreactive ES occurs. (C) 1997 Wiiey-Liss, Inc.