In last instar larvae of Gryllus bimaculatus, the prothoracic glands as well as the ovary and the abdominal integument synthesize and release ecdysteroids. Ovariectomy of day (d) 1 penultimate instar larvae extended the last larval stadium from 8 to 12 days (at 27ยฐC). Ecdysteroid titers in haemolymph and abdominal integument of ovariectomized d 6/7 last instar larvae were similar to those of d 4 intact larvae and of d 6/7 sham-operated animals. Net release of ecdysteroids (in vitro) by the abdominal integument from ovariectomized and sham-operated d 6 last instar larvae was twice that for intact d 4 specimens. Ovariectomy of d 1 last instar larvae strongly reduced levels of ecdysteroids in haemolymph and integument as well as release of ecdysteroids by the abdominal integument in 4-day-old adults. Allatectomy of d 1 last instar larvae also markedly reduced ecdysteroid titers as well as rates of ecdysteroid release by the abdominal integument and by the ovary of young female crickets. The results suggest a prominent role of the ovary in ecdysteroid synthesis of adult females and indicate a juvenile hormone-dependent control of ecdysteroid biosynthesis during vitellogenesis. Arch. Insect Biochem. Physiol. 35:149-158, 1997.