Developmental changes in the morphology and three-dimensional arrangement of antennal hair plates in crickets

Antennae of insects are essential mechanosensory organs that facilitate active tactile exploration and spatial navigation. Hair-plate sensilla at the base of the antenna flagellum provide proprioceptive inputs to detect their position. In hemimetabolous insects, such as crickets, the first instar immediately after hatching also possesses antennae, but the developmental dynamics and spatial organization of antennal hair plates remain poorly understood. Here, we present a comprehensive three-dimensional analysis of the antennal hair plates in crickets across developmental stages, from the first instar to adulthood. Using scanning electron microscopy and confocal laser scanning microscopy, we demonstrated that hair plate sensilla were present from the first instars and maintained a highly stereotyped spatial arrangement throughout development. Three-dimensional quantification revealed that new sensilla added during molting were formed at specific sites within the hair plate clusters that had existed at the previous stage, maintaining the spatial pattern despite the substantial growth of the antenna. Multidimensional analyses indicated that the spatial arrangement of sensilla was consistent across individuals, suggesting that organization was genetically determined. Retrograde labeling of sensory afferents showed that sensory neurons in the hair plates converged their axons, extended axon collaterals into the ipsilateral region of the antennal mechanosensory and motor center, and ultimately projected to the subesophageal ganglion. There was no apparent difference in their projection site among hair plates, suggesting no evidence of topographic organization. Our findings highlight the conserved spatial organization of hair-plate sensilla in crickets, suggesting a robust proprioceptive system that provides reliable feedback of antennal position throughout development.