Ecdysteroids in the American dog tick, Dermacentor variabilis (Acari: Ixodidae), during different periods of tick development.

Abstract

Ecdysteroids occur in all life stages of the American dog tick, Dermacentor variabilis . 20-hydroxyecdysone (20-OH ecdysone) and 2 other radioimmunoassay (RIA) positive fractions were found in engorged nymphs and adult ticks. 20-OH ecdysone and at least 1 RIA-positive fraction were found in the embryos and engorged larvae. No 20-OH ecdysone was found in the unfed larvae or unfed nymphs. Increases in total ecdysteroid content per tick occurred during ecdysial periods, adult feeding, and especially during female repletion and oviposition. In contrast, the total concentration declined gradually in fasting adults. In most cases, changes in the concentration of 20-OH ecdysone resembled the changes in total ecdysteroid content. With 1 exception, high-performance liquid chromatography (HPLC) gave substantially higher estimates of total ecdysteroid content in the various tick life stages or physiological states than did RIA. No relationship between the changes in the concentrations of ecdysteroids and sex pheromone (2,6-dichlorophenol) were observed. However, the foveal (pheromone) glands appeared to respond to exogenous 20-OH ecdysone; ultrastructural changes characteristic of actively secreting glands were found in unfed females following exposure to this hormone.