HUMORAL STIMULATION OF THE LARVAL AND ADULT PROTHORACIC GLANDS IN SCHISTOCERCA-GREGARIA

Fluctuations in ecdysteroid production by explanted prothoracic glands (PG) during the penultimate and last larval instars parallel changes in ecdysteroid titer in the hemolymph. The in vitro output of ecdyster oids increases up to 30-fold when PG are co-cultured with the brain. M aximal amounts of ecdysteroids are produced when both PG and brain are taken from larvae at the time of the molt-inducing ecdysteroid peaks (days 2-3 in the penultimate and days 5-6 in the last instar), and als o from day 3 last instar larvae that exhibit a small rise of hemolymph ecdysteroids. Detailed investigations on penultimate instar larvae re vealed that their PC become sensitive to the stimulation on day 1 (abo ut 24 h after ecdysis), but the stimulatory brain potential is restric ted to days 2 and 3. Both the stimulatory capacity of the brain and th e sensitivity of PC are lost on days 4 and 5, i.e., after the ecdyster oid surge on day 3. PC explanted from young adults do not secrete appr eciable amounts of ecdysteroids but can be stimulated to ecdysteroid p roduction with active larval brains. (C) 1997 Wiley-Liss, Inc.