Effects of exogenous ecdysteroid titer on endogenous ecdysteroid production in vitro by testes of the tobacco budworm,Heliothis virescens

Testes or the isolated sheaths of testes from late-last-instar larvae of the tobacco budworm, Heliothis virescens, spontaneously secreted ecdysteroids in vitro. Exogenous 20-hydroxyecdysone, incubated with the testes or isolated testis sheaths, functioned in a local positive feedback system to increase production of the several ecdysteroids typical of H. virescens testes. The increase in ecdysteroid production by testis tissue was dependent on discrete ranges in exogenous ecdysteroid titer. Activation ratios of 2–5 resulted from exogenous 20-hydroxyecdysone titers of 0.5 to 15 pg/μl, while activation ratios of 10–30 resulted from exogenous titers of 15–100 pg/μl of 20-hydroxyecdysone. Activation ratios approached 200 with exogenous titers of 100–1,000 pg/μl of 20-hydroxyecdysone.