Sensilla on antennae and mouthparts of adult spruce bark beetle Ips typographus (Coleoptera: Curculionidae)

The spruce bark beetle, Ips typographus, is an invasive forest pest that occurs across Eurasia. To further understand the mechanism of insect-host chemical communication and the feeding choices of adult I. typographus, we examined the sensilla on the antennae and mouthparts of I. typographus using scanning electron microscopy. No sexual dimorphism in sensilla type or distribution was observed. Ten subtypes of antennal sensilla were identified: sensilla trichodea Types I-III (TR1, TR2, and TR3); sensilla chaetica Types I and II (CH1 and CH2); sensilla basiconica Types I-III (BA(1), BA(2), and BA(3)); sensilla coeloconica (CO); and Bohm sensilla (BS). BA(2) were the most abundant among the antennal sensilla in both sexes. Thirteen mouthpart sensilla subtypes were observed: sensilla trichodea Types I-IV (TR1, TR2, TR3, and TR4); sensilla chaetica Types I-III (CH1, CH2, and CH3); sensilla digitiformia (DI); sensilla basiconica Types I-II (BA(1) and BA(2)); and sensilla styloconica Types I-III (ST1, ST2, and ST3). Among these, TR4 were the most abundant in both sexes. The apex of each maxillary and labial palp carried the same sensilla (BA(2), ST1, ST2, and ST3), although the apex of the maxillary palp contained more total sensilla. The functional roles of each sensilla type are discussed based on their external structure and distribution. The results provide a theoretical basis for further studies on the olfactory and feeding behaviors and electrophysiology of adult I. typographus.