Abstract: 【Aim】 This study aims to evaluate the effects of syringic acid on the lethal and sublethal effects of Lymantria dispar nucleopolyhedrovirus (LdNPV) against larvae of the gypsy moth, L. dispar, so as to provide a scientific basis for the prevention and control of this insect pest. 【Methods】 Diet plus was used to assess the lethal and sublethal effects of LdNPV with and without syringic acid on the 2nd instar larvae of L. dispar. 【Results】 The median lethal concentration (LC₅₀) values of LdNPV to the 2nd instar larvae of L. dispar fed on the artificial diets with and without syringic acid were 91.1 OBs/μL and 194.8 OBs/μL, respectively. The median lethal time (LT₅₀) values of LdNPV at the concentration of 2 400 OBs/μL to the 2nd instar larvae fed on the artificial diets with and without syringic acid were 9.3 and 10.1 d, respectively. The median lethal time (LT₅₀) values of LdNPV at the concentration  of 24 000 OBs/μL to the 2nd instar larvae fed on the artificial diets with and without syringic acid were 7.8 and 8.1 d, respectively. The higher the concentration of LdNPV, the lower the LT₅₀ value. Syringic acid added in the artificial diet enhanced the lethal effects of LdNPV against L. dispar larvae, and caused the lower LC₅₀ and LT₅₀ values of LdNPV against L. dispar larvae as compared with the diet without syringic acid. When the larvae were fed the artificial diet, the sublethal effects of LdNPV on larval duration, pupal duration and female adult longevity were not significant; when the LdNPV concentration was higher than 240 OBs/μL, however, the male adult longevity was shortened and the number of eggs laid per female was less than those of the control. The sublethal effects of LdNPV on L. dispar larvae fed on the artificial diet with syringic acid and high concentration of LdNPV were significant: the female and male larval duration was prolonged, the male adult longevity was shortened, and the male adult emergence rate and the number of eggs laid per female reduced. 【Conclusion】 The results suggest that syringic acid can enhance the virulence of LdNPV against L. dispar larvae and its sublethal effects on L. dispar.

Key words: Lymantria dispar; LdNPV, syringic acid, virulence, sublethal effect