REGULATION OF PROTHORACIC GLAND ACTIVITY IN DIAPAUSING LARVAE OF THE WAX MOTH, GALLERIA-MELLONELLA L (LEPIDOPTERA)

The development of Galleria mellonella is arrested by a lowered temperature of 18-degrees-C at the stage of the last instar post-spinning larva. The haemolymph ecdysteroid titre of these larvae is maintained at a low level of ca 5 pg of 20-hydroxyecdysone per mul. Different types of surgical manipulations including nerve cord-severance, implantation of the brain, prothoracic glands (PGs) or fat body accompanied with ecdysteroid titre measurements show that the tow ecdysteroid titre in diapausing larvae is due to nervous inhibition of their PGs. The inhibitory input probably comes from the brain and is transmitted down to the PGs via the suboesophageal ganglion and paired cervical nerves. Severance of the nerve tracts at any level caused rapid activation of PGs of diapausing insects. Nervous inhibition of the PGs ceases about 6-9 h after transfer of diapausing larvae from the lower temperature to the diapause-terminating conditions of 30-degrees-C. As long as the PGs are under nervous inhibitory control they are refractory to humoral stimulation. The brains of diapausing larvae exhibit in vitro high prothoracicotropic activity which suggests that PTTH is accumulated in the brain during diapause. The role of juvenile hormone in inhibiting the release of PTTH from the brain to haemolymph, and its effect on the PGs during diapause is discussed.