Larval testes of the tobacco budworm: a new source of insect ecdysteroids.

Testes of last-instar larvae of the tobacco budworm release five times more ecdysteroid into incubation medium (judged by radioimmunoassay) in 2.5 hours than is found in testis homogenates. Incubation of testicular components indicates that the testis sheath may be the site of ecdysteroid synthesis. Fractionation of hemalymph, testis homogenate, and incubation medium by high-performance liquid chromatography produces a distinct ecdysteroid pattern in each case. Thus, released testis ecdysteroids are probably converted to other forms for use, sequestration, or general circulation. Their functions are unknown.