Abstract: 【Aim】 This study aims to get more ultrastructure details of female and male adults of Culicoides arakawai (Arakawa) for accurate identification of biting midges. 【Methods】 The ultrastructure of female and male adults of C. arakawai was observed by scanning electronic microscope. 【Results】 A total of 31 electron micrographs of female and male adults of C. arakawai, including the features of compound eyes, antennae, mouthparts, wings, scutellum and postscutellum, legs and genitalia were obtained successfully. More accurate data of some features were obtained. For example, the length ratios of various segments of antennal flagella and palpi of female adults are 4.80:3.22∶3.56:3.54:3.44:3.56:3.56:3.86:7.32:6.96:7.02:7.40:9.78 and 2.90:7.47:8.07:2.58:3.92, respectively; the sizes of wings of female and male adults are 1.34-1.36 mm×0.56-0.66 mm and 1.22-1.32 mm×0.40-0.48 mm, respectively, and the size of spermatheca is 71.87 μm×48.07 μm. The poorly known features were observed, including female with 19 teeth of maxil arranged in 2 lines, male with 12-13 slender teeth of maxil, female trapeziform scutellum with 4 thick bristles and 6-8 thin bristles, female spur with hairs arranged fan-shaped on the surface, the terminal branch of claw, empodium of female with 4 pairs of hairy branches, spermatheca with punctations on surface, the width ratio of datum hole to spermatheca about 1/9, and hypopygium of male with microtrichia and macrochaeta and special structure in the inner surface. The ungual digitule was newly discovered. The sexual dimorphism was notable in antennal characteristics, type of sensilla, pattern, teeth, number and shape of mandible, and shape of tongue and wing between female and male adults. 【Conclusion】 The results provide useful information for the accurate identification of C. arakawai and for studying the taxonomy and phylogeny of Ceratopogouidae, and have significant economic and medical value.

Key words: Culicoides arakawai, blood-sucking midges, Culicoides, adult, morphology, ultrastructure, scanning electronic microscope