Regulation of larval corpora allata in Galleria mellonella

Abstract

IN insects metamorphosis occurs when the corpora allata stop secreting juvenile hormone, but it is not known how the production of juvenile hormone is regulated. Wigglesworth¹ first indicated that the nervous connections from the brain to the corpora allata provide a mechanism for control; this control could be nervous or neurohormonal. In many adult insects, the corpora allata seem to be inhibited via their nervous connections to the brain, since in most cases severing these nerves activates the glands^2,3. Whether the same is true for larvae has not been demonstrated conclusively. Activation of the corpora allata by neurosecretion has been demonstrated in many adult insects, for example Tenebrio molitor², Leptinotarsa decemlineata⁴ and Rhodnius prolixus⁵, and the production of an allatotropic hormone by the larval brain has also been suggested^6–8. We have now investigated the control of corpora allata function in last instar larvae of Galleria mellonella, encouraged by the discovery that in this species the implantation of brains at the beginning of the last larval instar causes an extra larval moult⁹. Our results show that the corpora allata are activated by a neurohumoral factor from the brain during larval development and that they are inactivated by nervous inhibition just before metamorphosis.