The chemosensory system of the clonal raider ant larva
Ant larvae are blind and immobile, depending heavily on the adults for care in the form of feeding, grooming, and transport. However, they are not inactive colony members but play a central role in the organization of ant societies by modulating adult behavior and physiology. While adult ants have been studied extensively, we still know little about what sensory modalities larvae use to perceive their environment. Here, we provide a molecular and circuit-level characterization of the chemosensory system of the clonal raider ant larva. Combining scanning electron microscopy and confocal imaging, we show that dome sensilla in the maxillary and labial palps are innervated by odorant receptor (OR) neurons. A larger population of ionotropic receptor (IR) neurons innervate papilla sensilla across various regions of the larval head: the antennae, the labrum, the maxillary palps and galeae, as well as the labial palps and the ventral labium. This suggests that IRs, which can have various functions, from taste and olfaction to temperature and humidity sensing, constitute the predominant chemosensory modality in ant larvae. To investigate projections into the central brain, we imaged transgenic lines that fluorescently label OR- and IR-expressing neurons. We found that OR- and IR-expressing neurons in the labium and maxilla project along the labial and maxillary nerves through the subesophageal ganglion to the deutocerebrum, whereas IR-expressing neurons from the labrum project to the tritocerebrum and those from the antenna project to the posterior deutocerebrum. Together, our findings establish a structural and molecular framework to study larval chemosensation in ants.