Effect of 20-hydroxyecdysone on the salivary glands of the male tick, Amblyomma hebraeum.

Female ticks (Acari: Ixodidae) feed only once in the adult stage, dying after laying a large batch of eggs. During the early post-engorgement stage, haemolymph ecdysteroid titre rises, which is probably responsible for autolysis of the salivary glands that takes place at this time. Males, on the other hand, can re-attach and feed numerous times during the adult stage. Males were fed on rabbits for either 7 or 14 days. Haemolymph was collected either the day of removal from the host or 4 days later, and ecdysteroid titre was measured by radioimmunoassay. The approximate titre in all 4 groups was 20 ng of 20-hydroxyecdysone (20-OHE) equivalents/ml haemolymph. Fluid secretory competence in vitro can be used as an index of salivary-gland degeneration. The glands dissected from fed males which had been left off the host for 4 days lost 62% of their fluid secretory competence compared to glands dissected shortly after the males were removed. This loss in fluid secretory competence was reversed by allowing ticks left off the host of 4 days to resume feeding. Male salivary glands lost fluid secretory competence when exposed for 4 days in organ culture to 20-OHE; the effect was maximal at the lowest concentration tested (20 ng/ml). Thus, although male salivary glands were highly sensitive to 20-OHE, it is still not clear whether this hormone causes the tissue to degenerate.