Noelle A. Granger

CONTROL OF CORPORA ALLATA FUNCTION IN LARVAE OF GALLERIA MELLONELLA

1. The implantation of three brains into freshly ecdysed last instar larvae which possess at least one of the two corpora allata induces extra larval development. Implanted brains appear to produce a neurohumoral allatotropic factor.2. Corpora allata seem to be inhibited via their nervous connections 48-60 hours after the last larval-larval ecdysis and become insensitive to the allatotropic factor. Severance of the nerves innervating the corpora allata and adjacent corpora cardiaca induces extra larval development in 7% of the experimental insects and restores sensitivity to the implanted brains in as many as 20%.3. Severance of the nerves to the corpora cardiaca—corpora allata complexes or implantation of corpora cardiaca—corpora allata complexes into allatectomized larvae in some instances causes a considerable prolongation of the last larval instar. It is suggested that disconnection of the corpora allata from the brain partly removes their inhibition and induces secretion of a low titer of juvenile ho...

Control of prothoracic gland activity in larvae of Galleria mellonella

Abstract Prothoracic glands of last instar wax moth larvae maintain spontaneous secretory activity both in decapitated larvae and in isolated abdomens into which they have been transplanted, as judged by their ability to induce secretion of a new cuticle. Their activity is hormonally stimulated by the brain and inhibited by the prothoracic and mesothoracic ganglia. The subesophageal ganglion seems to suppress the inhibitory influence of the thoracic ganglia. The prothoracic glands of larvae decapitated at different times during the last instar all respond to brain implantation, and this response does not change when brains are implanted at increasing intervals after decapitation. The prothoracotropic activity of the isolated brain is highest in brains of pupae and adults but is relatively and consistently low in brains of last instar larvae. The results demonstrate that the control of prothoracic glands is a complex process governed by the nervous integration of various stimuli.

The allatotropic activity of the larval brain of Galleria mellonella cultured in vitro

The brains of last instar larvae of Galleria mellonella can be successfully cultured in vitro. The high allatotropic activity of 0–8 hr brains, as measured by their ability to elicit supernumerary larval molts upon implantation into 0–8 hr last instar larval hosts, remains constant through 4 days in vitro. The allatotropic activity of 120 hr brains increases during in vitro culture. The number of supernumerary larvae resulting from the implantations of 120 hr brains rises from 20 to 30% of the hosts implanted with fresh brains, to 90% of the hosts supplied with brains maintained in vitro for 24 hr prior to implantation. There is a progressive loss of paraldehyde-fuchsin-stainable neurosecretory material over 72 hr of in vitro culture from the three groups of neurosecretory cells visible in whole mounts of the brains. Nevertheless, the ultrastructural picture of the medial neurosecretory cells, which are the probable source of the allatotropic factor, indicates synthetic activity after 72 hr of culture. In 0–8 hr last instar brains which are cultured for 48 hr as complexes with attached corpora cardiaca and corpora allata, stainable neurosecretory material accumulates in all three groups of cerebral neurosecretorycells. The brains from the cultured complexes have low allatotropic activity. It is concluded on the basis of the bioassay and ultrastructural observations that under our conditions of in vitro culture, the neurosecretory cells of the last instar larval brain not only survive but also maintain synthetic activity through at least 72 hr in vitro. The relationship between stainable neurosecretory material and neurosecretory activity in this system is discussed, as are possible feedback interactions involving the corpora cardiaca-corpora allata and the brain.

Ultrastructure of the protocerebral neurosecretory cells of larval Galleria mellonella, in situ and after culture of the brain in vitro.

Three major groups of neurosecretory cells are described in the larval brain of Galleria mellonella at two different times during the last larval instar and in larval brains after 72 hr of culture in vitro. The medial group in vivo consists of four distinct neurosecretory cell types, based on characteristic size and morphology, while the posterior and lateral groups each contain a single distinct type of neurosecretory cell. Morphological differences between the same neurosecretory cells at the different times during the last instar are most apparent in the lateral L-1 cells and in the medial M-2 cells, where pleiomorphism is particularly evident in the size, density and accumulations of neurosecretory granules. The only neurosecretory cells in which apparent synthesis of neurosecretory granules is still observed after culture of the brain in vitro are the medial M-2 cells. The other neurosecretory cell types show no accumulation of neurosecretory granules nor new synthesis of neurosecretory material, but are similar to neurosecretory cells in the brain in vivo in all other respects. The morphology of the neurosecretory cells in the larval brain in vivo and in vitro is discussed in relation to their appearance at the light microscopic level and to a known neurohormonal function of the brain which is maintained during 72 hr in vitro.

Innervation of the prothoracic glands in Galleria mellonella larvae (Lepidoptera: Pyralidae)

Abstract The prothoracic glands in larvae of Galleria mellonella are innervated by branches of 4 pairs of nerves: the lateral segmental nerves of the subesophageal ganglion, the lateral segmental and median nerves of the prothoracic ganglion, and nerves emerging from the prothoracic-mesothoracic interganglionic connectives. The nerve cells in the thoracic ganglia supplying these nerves were mapped using cobalt chloride impregnation. The lateral segmental nerves of the subesophageal ganglion are derived from 3 cells located along the midline of the ganglion. The lateral segmental nerves of the prothoracic ganglion originate from somata in both the prothoracic and subesophageal ganglia. Six nerve cells aligned across the posterior half of the prothoracic ganglion supply both median nerves, and the nerves emerging from the interganglionic connectives derive from somata in both the prothoracic and mesothoracic ganglia. This pattern of innervation provides anatomical evidence to support previous experimental studies indicating that interactions of the first 3 thoracic ganglia modulate gland activity.