Neuroendocrine influence on haemolymph protein concentration and midgut protease activity in the final instar larva of Tramea virginia (Rambur) (Anisoptera: Libellulidae)

The haemolymph protein concentration increased throughout most of the intermoult period of the final instar larvae, but decreased sharply a few days before emergence. Treatment with Farnesyl methyl ether caused no significant change in the haemolymph protein concentration. However, cauterization of the medial neurosecretory cells (MNC) of the brain caused depletion, while administration of an aqueous extract of corpora cardiaca (CC) elevated the level of haemolymph protein. Cauterization of the MNC and removal of the CC caused significant reduction in the midgut protease activity. These results collectively suggest the profound influence of the MNC hormone on protein metabolism, mostly mediated through the midgut protease activity.