Metabolism of ecdysteroids in the female tick Amblyomma hebraeum (Ixodoidea, Ixodidae): accumulation of free ecdysone and 20-hydroxyecdysone in the eggs.

[3H]-20-hydroxyecdysone ([3H]-20E) injected into Amblyomma hebraeum females 7 days before the beginning of oviposition, viz. at the beginning of vitellogenesis, was converted to 3 polar peaks of unknown nature called 1, 2 and 3, and to apolar conjugates AP1, AP2 and AP3. AP2 have the same retention times as the esters of 20E with long chain fatty acids described in Ornithodoros moubata (Diehl et al. 1985). However, principally unmetabolized 20E was incorporated into the ovaries, and 16% of the injected labelling was recovered in the eggs, 3/4 being free 20E. When 20E was injected during oviposition, it was not converted to the polar products but only to the apolar products. At this time, 76% of the total radiolabel injected accumulated in the egg-batch, principally in the form of free unmetabolized 20E. After injection of [3H]-ecdysone ([3H]-E), the three polar metabolites 1', 2' and 3', probably 20-deoxy homologues of 1, 2 and 3 described above were always produced irrespective of the time of injection. In addition, E was metabolized to 20E and to the apolar conjugates AP1, AP2, and AP3. E, 20E and peak 2' were incorporated into the ovary within the first day after injection. These 3 compounds were found in freshly laid eggs in variable proportions, the quantity of E decreasing with time while 20E and peak 2' increased. At the end of oviposition, ca. 60% of the injected radiolabel had been incorporated into the eggs. Apolar products and polar metabolites accumulating in the body were apparently not used as a source of free hormone for the eggs. Our results with tritiated ecdysteroids confirm our data concerning endogenous ecdysteroids of the eggs of A. hebraeum (Connat et al. 1985). This species, in contrast to 2 other female ticks, Ornithodoros moubata and Boophilus microplus, incorporates free E and 20E instead of ecdysteroid conjugates into its eggs. The role of these free ecdysteroids remains to be elucidated.