The ubiquitous yet diverse associations between insects and fungi have long evolved. At the same time, the interactions between beetles, microbes, and hosts have not been well documented, especially for new fungi taxa. Two interesting specimens of Akanthomyces were found on adult moths of Dudusa sphingiformis in Yunnan Province, Southwest China. These specimens were identified as a new species based on morphology and phylogeny. Akanthomyces bannaensis sp. nov. is characterized by being determined to occur on an adult of Dudusa sphingiformis and synnemata arising from a moth body up to 5 cm long and 0.1-1.3 mm wide, unbranched, cylindrical to clavate with acute or blunt end. The morphological identification and phylogenetic analysis of combined ITS, nLSU, and RPB2 sequence data support A. bannaensis as a new species, in which A. bannaensis is sister to A. pyralidarum. A full description, illustrations and phylogenetic analysis results of the new species are provided.