Abstract:The gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae), is a polyphagous defoliator of Eurasian origin known to feed on over 300 species of trees and shrubs and distributed in North America and North Africa at present. It's one of the most serious insect pests causing great economic losses on forest production. Gypsy moth nucleopolyhedrovirus (LdMNPV) plays an important regulatory role and is one of the major factors controlling L. dispar populations and often causes the population collapse. Three isolates of gypsy moth virus from China (LdMNPV-H), Japan (LdMNPV-J) and the registered strain from North America (LdMNPV-D) were evaluated on the virulence against the 2nd instar Asian gypsy moth larvae fed on poplar at laboratory. Tinopal LPW, a UV protection brightener, was added into the solution of LdMNPV isolates to compare the virulence against the same instar larvae. UV protection of Tinopal LPW was tested using a UV lamplight (30W) radiation. The results showed that Tinopal LPW could enhance the biological activity of the virus, and the higher concentration of Tinopal LPW, the higher activity of the virus. The optimal concentration of Tinopal LPW was 1%. The results also indicated that LdMNPV-D and LdMNPV-H did not differ significantly in LC50 when tested against the Asian gypsy moth larvae fed on poplar (Popul uscathayana) regardless of adding the brightener of Tinopal LPW. LdMNPV-J and LdMNPV-D differed significantly in LC50, and so did LdMNPV-J and LdMNPV-H. The LC50s of LdMNPV-D, LdMNPV-H and LdMNPV-J with 1% Tinopal LPW were 1.0, 1.6 and 17.6 OBs/μL, respectively, whereas those without 1%Tinopal LPW were 32.9, 39.0 and 1076.4 OBs/μL, respectively. The LC95s of LdMNPV-D, LdMNPV-H and LdMNPV-J with 1% Tinopal LPW were 73.0、285.4 and 2360.8Bs/μL, respectively, whereas those without 1%Tinopal LPW were 2125.5、1275.8 and 303540.0 OBs/μL, respectively. The virulence of the three isolates were increased 33, 24 and 61 times by 1%Tinopal LPW in LC50, respectively. In addition, the LT50s of the three isolates with 1%Tinopal LPW were 2.9d, 5.3d and 1.2d shorter than those without 1%Tinopal LPW. LdMNPV-H and LdMNPV-D showed lower LC50, shorter LT50 and bigger slopes against Asian gypsy moth, and their virulences were higher than that of LdMNPV-J. LdMNPV-D with 1% Tinopal LPW should be chosen to use in practice. 1%Tinopal LPW had UV radiation protection on the LdMNPV isolates. After 16 hours exposure to a 30W UV lamplight at a distance of 40cm, the virulences of LdMNPV-D, LdMNPV-H and LdMNPV-J with 1% Tinopal LPW were 1.8, 2.6 and 1.8 times higher than those without 1% Tinopal LPW, respectively.