Six different geographical sources of Lymantria dispar (L.) and Lymantria mathura (L.) in the People's Republic of China were sampled for nucleopolyhedrosis virus. Comparative bioassays of the L. dispar sources showed the U.S. Hamden standard to be more effective than the PRC nucleopolyhedrosis viruses. The L. mathura NPV equalled the effectiveness of the Hamden standard even after 3 passages in lab reared L. dispar larvae. This is the 1 st report of L. mathura NPV effect on a U.S. strain of L. dispar.The gypsy moth, Lymantria dispar (L.), is the dominant pest of oak forests in the United States of America. Field collection, identification and evaluation of L. dispar pathogens revealed that the nucleopolyhedrosis virus is the most important pathogen in the U.S.A., particularly in moderate to dense populations (Podgwalte & Campbell, 1971). However, the search for additional biorationals for controlling gypsy moth continues. During May to July, 1982, a U.S. scientific team traveled in the People's Republic of China (PRC) to collect gypsy moth and identify and evaluate potential biological controls under an agreement between the USDA's Office of International Cooperation and Development and the Chinese Bureau of Forestry.We know of no cross-infectivity studies of Asian and North American congeneric Lymantriids. We report here the first details of comparative bioassay of Chinese Lymantriid NPVs against North American L. dispar larvae.Extensive field collections of over 9000 gypsy moth larvae and 600 Lymantria rnathura Moore were made from 6 different locations in the PRC ( fig. 1). Larvae were reared by separate location and species and held in cardboard boxes on oak foliage. L. dispar larvae killed by NPV were transferred to glass vials and brought to the U.S. Forest Services's Center for Biological Control of Northeastern Forest Insects and Diseases and stored at -0.7 ~ for further processing.Comparative bioassays were conducted.against F24 insectary-reared L. dispar larvae with the 6 geographic isolates of L. dispar NPV from the PRC, 1 pooled isolate of L. mathura NPV (serial passage), and the Hamden standard L. dispar NPV isolate from the U.S. All materials were bioassayed by diet incorporation of purified polyhedral inclusion body (PIB) inocula in serial dilutions (Lewis et al., 1981) the highest being 10 s PIB/ml. The L. mathura NPV affects F24 L. dispar larvae as well as the primary Hamden standard, but is not significantly different (table 1). This is the first report of any Lymantriid NPV not collected from L. dispar exhibiting as pathcg.-~;o a response to U.S.L. dispar larvae as the
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