Abstract:The technique of using the pupae of Chinese tussah, Antheraea pernyi, as a surrogate host to artificially rear Chouioia cunea has been playing an important role in the biological control of the fall webworm, Hyphantria cunea, in Liaoning, Beijing, Tianjin, Shanghai, Hebei, Shandong Provinces or Municipalities and other places of China. Bacterial diseases of Chinese tussah pupae are the main obstacle to mass rearing C. cunea. Based on the fact that the tissue in some pupae turned pink after liquefying during rearing C. cunea, which is a typical symptom of an unknown bacterial disease, a bacterium was isolated and purified, and C3 was obtained. C3 was identified as a strain of Serratia marcescens by conventional techniques, Biolog system and 16S rRNA analysis, and was determined as the pathogenic bacterium causing the disease to Chinese tussah pupae by a test based on Koch’s postulates. The identification characteristics were described of the disease in its incidence in the process of rearing C. cunea.