Functional spatial organization of antennal hair plate sensilla and their development 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 the antennae's position. In hemimetabolous insects, such as crickets, the first instar immediately after hatching also possesses antennae; however, the developmental dynamics and spatial organization of antennal hair plates remain poorly understood. We present a comprehensive three-dimensional analysis of the antennal hair plates in crickets (Gryllus bimaculatus) across developmental stages, from the first instar to the adult stage. We demonstrated that hair plate sensilla were present from the first instar 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 their organization was under genetic control. Anterograde 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 the projection sites among the hair plates, suggesting no clear 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 on antennal position throughout development.