Sensilla Types And Ultrastructure Of Dendroctonus Armandi(Coleoptra:Scolytidae)

Chinese white pine beetle, Dendroctonus armandi Tsai et Li (Coleoptera:Scolytidae), an invasive forest pest in Qingling Mountains (Pinus armandi Fr.(Pinaceae)), is highly dependent on its olfactory system (especially the chemical sensilla) for activities such as host seeking, mating, oviposition and population aggregation. The research aimed at observing its sensilla distribution and ultrastructure in order to reveal its olfactory system mechanism.In this research, scanning electron microscopy and transmission electron microscopy were used to observe the sensilla on the overall surface of adult D. armandi and its larvae. We found the following results:(1) There are different types of sensilla found on the adult Chinese white pine beetles surfaces of their heads, fore legs, membranous wings and elytra. We described7morphological types of sensilla on the surface of adult D. armandi:sensilla trichodea, sensilla chaetica, sensilla basiconica, sensilla styloconica, sensilla campaniformia, bohm bristle and bud-shaped sensilla; and bohm bristle, sensilla styloconica, sensilla basiconica are found on the overall surface of the larvae.(2) The findings observed by scanning electron microscopy:The heads are the primary sensory organs of adult bark beetles, especially the antennae. The main types of sensilla on the antennae are sensilla trichodea, sensilla chaetica, sensilla basiconica, bud-shaped sensilla and sensilla campaniformia. Sensilla trichodea and sensilla chaetica are found on the compound eyes, while sensilla basiconica, sensilla styloconica and sensilla chaetica are observed on the mouthparts. There are sensilla campaniformia and sensilla trichodea on the forelegs, where the average numbers of the sensilla campaniformia are obviously different between male and female adult bark beetles. We found sensilla trichodea on the round sag area with the cuticular pores of the elytra, and Bohm bristle and sensilla chaetica distributed regularly on the membranous wings.(3) The findings observed by transmission electron microscopy:the sensilla trichodea are unilaminar cuticle sensilla with pores along the surface making sensory processes to the dendrites in the lumen; the sensilla chaetica have three to four layers cuticle but no pores; the zigzag microtriches are composed by cuticle without any nervous structure.We can draw a conclusion:the sensilla trichodea are olfactory organs proved by their morphology and ultrastructure; the sensilla chaetica do not have the olfactory function; the zigzag microtriches are not sensilla.