HORMONAL-CONTROL OF MOLTING AND REPRODUCTION IN TICKS

Among ticks there are two developmental and three reproductive pattern s that correlate with taxonomic groupings (Argasidae, prostriate and m etastriate Ixodidae). Feeding is a prerequisite for molting; feeding a nd mating are necessary for reproduction in all except a few parthenog enetic species. Growth and development in ticks and other chelicerates appear to be controlled by molting hormones (ecdysteroids), as they a re in insects and crustaceans. Ecdysone and 20-hydroxyecdysone appear to be present in most or all of the major chelicerate taxa. Epidermis is the site of ecdysone production and fat body the site of 20-hydroxy lation in the argasid Ornithodoros parkeri, as is probably the case in all ticks. Ecdysteroids influence early stages of spermatogenesis by stimulation of DNA synthesis in spermatocytes, but controls for later stages of meiosis are unknown. A polypeptide (12,000 daltons) from mal e genital accessory glands stimulates capacitation (maturation) of spe rmatids into sperm at the time of spermatid transfer to females. Knowl edge of control of egg development and oviposition is incomplete. Stim uli from the synganglion are necessary for completion of oogenesis and two synganglial factors have been proposed. An Egg Development Stimul ation Factor (EDSF) in O. parkeri is synthesized and/or released three to six days after feeding. Vitellogenesis Inducing Factor (VIF) in O. moubata is synthesized and/or released within one hour after feeding. The VIF is hypothesized to impact an unidentified tissue which in tum produces a Fat Body Stimulation Factor (FSF) that stimulates fat body to synthesize vitellogenin (Vg). Roles of ecdysteroids and juvenile h ormones during egg development and oviposition are unclear.