Ultrastructural and morphological observations of the external and internal structures of the adult midge <i>Culicoides grisescens</i> (Diptera: Ceratopogonidae)

The external and internal structures of adult males and females of Culicoides grisescens Edwards were examined using scanning electron microscopy (SEM) and tissue sectioning techniques. Specimens were collected from Qilian Mountain National Park in Qinghai Province, China. The ultrastructure and morphology of the compound eyes, antennae, maxillary palpi, spermathecae, genitalia, and other structural features both male and female adults of C. grisescens are described. Significant morphological differences between the two sexes were observed. The female has a pair of large mandibles with 16 teeth arranged in two rows. The first row contains 16 teeth, while the second row is located near the terminal teeth at the lower part. In contrast, the male mandibles have 2 to 3 teeth, totaling over 20, with a slender structure and small teeth distributed near the center at the terminal end of the mandibles. The tip of the male tongue is narrower and triangular than in shape compared to the female. Additionally, there are significant differences in the shape of the antennae and the types of antennal sensilla between males and females. This study also observed that the middle lobe of the male masculine stem is V-shaped, and the terminal end of the masculine lateral process is bifurcated, featuring 5 to 7 slender, finger-like branches. These unique morphological structures are useful for distinguishing male Culicoides from each other. For the first time, this paper describes the internal structures of this species, including histological sections of the digestive, nervous, respiratory, and reproductive systems. The findings presented herein provide both visual and descriptive details for the systematic taxonomic study of Ceratopogonidae, highlighting their significant economic and medical importance.