Sensilla on the maxillary palp of cave and surface-dwelling species of the genus Tachycines (Orthoptera: Rhaphidophoridae)

Due to caves' environmental features (e.g., darkness and food limitation), cave-dwelling insects have evolved well-developed sensory systems. The habitats of the camel crickets of Tachycines are diverse, found both in cave and surface ecosystems. This study aims to clarify the sensilla types and distribution on the maxillary palp in male adults of the surface-dwelling Tachycines huaxi and cave-dwelling Tachycines shuangcha. The morphology and sensilla on the maxillary palp were observed using scanning electron microscopy. The maxillary palps of the two Tachycines species consist of five segments with varying lengths. Seven types of sensilla were recorded on maxillary palp of both species: sensilla chaetica (Sc.1–3), sensilla trichodea (St.1–2), sensilla palmatum (Sp), Böhm's bristles (Bb), sensilla campaniformia (Sca), sensilla basiconica (Sb.1–4), and sensilla coeloconica (Sco). The sensilla are primarily located on the fifth palpomere ofmaxillary palp. Sb.2 were found exclusively on maxillary palp of the species T. huaxi. The distribution of sensilla was similar between T. shuangcha and T. huaxi, but sensilla of the two species differed in length, diameter, and number. The potential functions of these sensilla, and possible morphological adaptations to the cave environments exhibited by the maxillary palp of the cavernicolous T. shuangcha are discussed.