Distribution of neuropeptides in the antennal lobes of male Spodoptera littoralis.

Olfaction is an important sensory modality that regulates a plethora of behavioural expressions in insects. Processing of olfactory information takes place in the primary olfactory centres of the brain, namely the antennal lobes (ALs). Neuropeptides have been shown to be present in the olfactory system of various insect species. In the present study, we analyse the distribution of tachykinin, FMRFamide-related peptides, allatotropin, allatostatin, myoinhibitory peptides and SIFamide in the AL of the male Egyptian cotton leafworm, Spodoptera littoralis. Immunocytochemical analyses revealed that most neuropeptides were expressed in different subpopulations of AL neurons. Their arborisation patterns within the AL suggest a significant role of neuropeptide signalling in the modulation of AL processing. In addition to local interneurons, our analysis also revealed a diversity of extrinsic peptidergic neurons that connected the antennal lobe with other brain centres. Their distributions suggest that extrinsic neurons perform various types of context-related modulation.