Morphology and distribution of mouthpart sensilla in Halyomorpha halys (Hemiptera: Pentatomidae): insights into feeding biology

The brown marmorated stink bug Halyomorpha halys (Hemiptera: Pentatomidae) is a globally invasive pest, but detailed information on the ultrastructure and sensory organization of its mouthparts remains incomplete. Using scanning electron microscopy, we examined the piercing-sucking apparatus of H. halys adults, focusing on sensilla morphology, number, and distribution. The mouthparts consist of the labrum, four-segmented labium, and paired mandibular and maxillary stylets. Twelve types of sensilla were identified and classified into six categories: basiconica, campaniformia, chaetica, coeloconica, styloconica, and trichodea. The labrum and labium emerged as primary sensory regions, integrating mechanical, chemical, and physical inputs. Sensilla campaniformia, chaetica, and trichodea are mainly interpreted as mechanoreceptors. Sensilla coeloconica have been associated with thermo- and hygroreception, contributing to the detection of physical parameters. The apical sensory fields host basiconica, styloconica, and specialized chaetica, likely mediating gustatory, olfactory, and thermo-hygroreceptive functions during host evaluation. Based on the characacteristics observed at the II-III and III-IV transition areas, an alternative labial position was hypothesied, potentially facilitating stylet cleaning and allowing modulation of insertion angle into plant tissues. This study provides the first comprehensive account of the mouthpart sensilla of H. halys, emphasizing their functional significance and species-specific traits. The morphological and functional insights gained here contribute to a deeper understanding of feeding biology in Pentatomidae and may support the development of innovative approaches for monitoring and managing this invasive pest.