Hormonal Control of Molting and Reproduction in Ticks

SYNOPSIS. Among ticks there are two developmental and threereproductive patterns that correlate with taxonomic groupings(Argasidae, prostriate and metastriate Ixodidae). Feeding isa prerequisite for molting; feeding and mating are necessaryfor reproduction in all except a few parthenogenetic species.Growth and development in ticks and other chelicerates appearto be controlled by molting hormones (ecdysteroids), as theyare in insects and crustaceans. Ecdysone and 20-hydroxyecdysoneappear to be present in most or all of the major cheliceratetaxa. Epidermis is the site of ecdysone production and fat bodythe site of 20-hydroxylation in the argasid Ornithodoros parkeri,as is probably the case in all ticks. Ecdysteroids influenceearly stages of spermatogenesis by stimulation of DNA synthesisin spermatocytes, but controls for later stages of meiosis areunknown. A polypeptide (12,000 daltons) from male genital accessoryglands stimulates capacitation (maturation) of spermatids intosperm at the time of spermatid transfer to females. Knowledgeof control of egg development and oviposition is incomplete.Stimuli from the synganglion are necessary for completion ofoogenesis and two synganglial factors have been proposed. AnEgg Development Stimulation Factor (EDSF) in O. parkeri is synthesizedand/or released three to six days after feeding. VitellogenesisInducing Factor (VIF) in O. moubata is synthesized and/ or releasedwithin one hour after feeding. The VIF is hypothesized to impactan unidentified tissue which in turn produces a Fat Body StimulationFactor (FSF) that stimulates fat body to synthesize vitellogenin(Vg). Roles of ecdysteroids and juvenile hormones during eggdevelopment and oviposition are unclear.