Abstract: 【Aim】 This study aims to characterize the morphology of sensilla on labial palps and the central projection of their sensory neurons in adults of the diamondback moth, Plutella xylostella. 【Methods】 The structures of labial palps and their sensilla type were observed under light and scanning electron microscopy, and the central projection of the sensory neurons of sensilla on labial palps were observed by using neuronal backfills and confocal microscope. 【Results】 The labial palp of P. xylostella adults consists of three segments, on which there are five types of sensilla, including Böhm bristles, sensilla campaniformia, sensilla squamiformia, sensilla basiconica, and microtrichia, and a labial-palp pit organ (LPO). Böhm bristles are spine-like, sensilla campaniformia have circular dome surrounded by a cuticular rim, and both of the two sensilla were found only on the 1st segment of labial palp, without significant differences in size between sexes. Sensilla squamiformia are willow leaf-like, sensilla basiconica are thick and straight, and both are scattered on the 2nd and 3rd segments, with significant differences in size between sexes. Sensilla squamiformia in females are significantly larger than those in males, and this sexual dimorphism suggests that this type of sensilla of female are likely associated with sensing of host plant odours. The LPO is located in the middle and upper part of the 3rd palpus segment, and the width of the pit is 5.68±0.33 μm in males and 6.03±0.23 μm in females, without significant difference between sexes. Many microtrichia with smooth surface are located in inner pit. The sensory neurons on the labial palp project to the subesophageal ganglion, labial pit organ glomerulus (LPOG) in each antennal lobe and the ventral nerve cord. 【Conclusion】 The morphology of sensilla on labial palps and the central projection of their sensory neurons in P. xylostella adults have been illustrated in this study, providing a basis for further investigation on their physiology and function.

Key words: Plutella xylostella, labial palp, sensilla, labial-palp pit organ, sexual dimorphism, nerve projections, ultrastructure