Nanopores on antennal chemosensilla in the fall armyworm, Spodoptera frugiperda

Olfactory sensilla on the antennae of insects detect important airborne chemical signals from the environment. We examined the antennal olfactory sensilla of Spodoptera frugiperda, a major crop pest and significant global biosecurity threat, using high-resolution scanning electron microscopy (SEM) to investigate its peripheral olfactory sensory system. Six major types of chemo-sensilla were identified according to their shape and further classified by size. Among them, sensilla trichodea, basiconica, and auricillica exhibited multiple nanopores on their cuticular surface, indicating that their primary sensory function is olfaction. Sensilla coeloconica likewise displayed nanopores between the adjacent columns of the central peg, further suggesting it plays a role in olfaction. In contrast, chaetic and peg sensilla contained one or a few pores at the sensillum tip with no multiple surface nanopores, indicating gustatory or other non-olfactory sensory functions. The shape, size, density, and distribution of surface nanopores were characteristic of each type and subtype of olfactory sensilla, suggesting that these morphological features may be associated with specific sensory functions of each olfactory sensillum. The current shape, size, and density of surface nanopores may represent an evolutionary compromise between odor sensitivity and mechanical stability in each type of olfactory sensilla. Our results provide new insights into the olfactory sensory system of S. frugiperda. Further electrophysiological and ultrastructural studies, such as single sensillum recording and transmission microscopy, will be useful to understand the functional architecture of the chemical communication system in S. frugiperda.