Allatostatin-like and AKH/HrTH-like peptides in the aphid Megoura viciae

Knowledge of the structures of neuropeptides that regulate development, metabolism, and behaviour in insects is extensive, but nothing is known of the identity of regulatory peptides in the aphid neuroendocrine system. The present study applies a radioimmunoassay to reveal the existence of at least two allatostatin-like peptides in the aphid, Megoura viciae. Immunocytochemistry using antibodies recognising cockroach and dipteran allatostatins (Dip-AST-7 and Cav-AST-1) revealed the presence of allatostatin-like peptides in the protocerebrum of the brain, in the supraoesophageal ganglion, and in the fused thoracic ganglia. Both the corpora cardiaca and the corpus allatum, as well as the nervi corporis cardiaci I, stained strongly with the allatostatin antibodies. AKH/ HrTH-like peptides were detected in extracts of M. viciae using conspecific bioassays for hypertrehalosaemic and hyperlipaemic activity. Endocrine cells of the corpora cardiaca contained AKH-like material that reacted to antibodies directed to the N- and C-terminus of Lom-AKH-I. Antibodies specific for the C-terminus of Lom-AKH-I gave extensive staining in the brain and immunoreactive fibres were also found in the suboesophageal and fused thoracic ganglia. In contrast, staining with antibodies recognising the N-terminus of Lom-AKH-I was restricted to the corpora cardiaca and a region of the pars intercerebralis. There was no difference between apterous and alate morphs of M. viciae in the distribution of both AKH-like and allatostatin-like peptides. These results suggest an endocrine role for AKH/HrTH and allatostatin-like peptides in aphids.