Ultrastructure of sensilla on the maxillary and labial palps of the adult Xylotrechus grayii (Coleoptera: Cerambycidae).

The longhorn beetle, Xylotrechus grayii (White, 1855), is a serious woodborer pest of many economic and medicinal plants. The maxillary and labial palps of X. grayii adults are strongly involved in mating and host selection behaviors. To further develop control strategies of the pest, sensilla on the palps were studied with scanning and transmission electron microscopy. Five types of sensilla (nine subtypes) were identified: sensilla styloconica (four subtypes, Sty1-4), sensilla chaetica (2 subtypes, SC1-2), sensilla digitiformia (Di), sensilla basiconica (Ba), and Böhm sensilla (Bm). Sty and Ba have dendrites and wall pores. SC2 has a tubular body. Di exist only on the terminal segment of the maxillary palp. Sty numbers are the highest in both palps, followed by SC. The number of sensilla in the maxillary palp is significantly higher than that in the labial palp. There are no significant sexual differences in sensilla types, characteristics, distribution, and quantity in the maxillary or labial palps, except for the number of SC sensilla on the maxillary palp. Sensilla functions were compared with correlative sensilla in previous studies. Sty may be sense gustation and olfaction stimulation, while SC are mechanoreceptors. Ba are likely thermo- and hygroreceptors. The phylliform depression area formed by Di may exert multiple functions. Bm may sense palp position and movement. These results contribute to the study of the electrophysiology and behavior mechanisms of X. grayii.