Abstract The papaya mealybug, Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae), highly polyphagous and now widespread, was discovered in Mengla County, Yunnan Province, China. The present study is aimed at confirming the identity of P. marginatus in mainland China based on its morphology and using molecular methods. Mitochondrial genes for cytochrome oxidase I (CO-I) were sequenced from 2 samples of P. marginatus. Homologous DNA sequences of P. marginatus, Phenacoccus solenopsis Tinsley and Coccus viridis (Green) (Hemiptera: Coccidae) - as an outgroup -were downloaded from Gen Bank. The morphology of putative P. marginatus specimens was examined using the same specimens as were subsequently used for the molecular study. Key morphological traits are described and illustrated. A 746 bp fragment of the CO-I was analyzed for the identification of P. marginatus. A phylogenetic tree was generated with the DNA sequences of all the mealybug species used in this study. The tree inclu...