Global and local modulatory supply to the mushroom bodies of the moth Spodoptera littoralis

The moth Spodoptera littoralis, is a major pest of agriculture whose olfactory system is tuned to odorants emitted by host plants and conspecifics. As in other insects, the paired mushroom bodies are thought to play pivotal roles in behaviors that are elicited by contextual and multisensory signals, amongst which those of specific odors dominate. Compared with species that have elaborate behavioral repertoires, such as the honey bee Apis mellifera or the cockroach Periplaneta americana, the mushroom bodies of S. littoralis were originally viewed as having a simple cellular organization. This has been since challenged by observations of putative transmitters and neuromodulators. As revealed by immunocytology, the spodopteran mushroom bodies, like those of other taxa, are subdivided longitudinally into discrete neuropil domains. Such divisions are further supported by the present study, which also demonstrates discrete affinities to different mushroom body neuropils by antibodies raised against two putative transmitters, glutamate and γ-aminobutyric acid, and against three putative neuromodulatory substances: serotonin, A-type allatostatin, and tachykinin-related peptides. The results suggest that in addition to longitudinal divisions of the lobes, circuits in the calyces and lobes are likely to be independently modulated.