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 (TR 1 , TR 2 , and TR 3 ); sensilla chaetica Types I and II (CH 1 and CH 2 ); sensilla basiconica Types I–III (BA 1 , BA 2 , and BA 3 ); sensilla coeloconica (CO); and Böhm 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 (TR 1 , TR 2 , TR 3 , and TR 4 ); sensilla chaetica Types I–III (CH 1 , CH 2 , and CH 3 ); sensilla digitiformia (DI); sensilla basiconica Types I–II (BA 1 and BA 2 ); and sensilla styloconica Types I–III (ST 1 , ST 2 , and ST 3 ). Among these, TR 4 were the most abundant in both sexes. The apex of each maxillary and labial palp carried the same sensilla (BA 2 , ST 1 , ST 2 , and ST 3 ), 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 .