Influence of phenolic acids on the lethal and sublethal effects of LdMNPV against spongy moth larvae, Lymantria dispar (Lepidoptera: Lymantriidae)

The multicapsid nucleopolyhedrovirus of Lymantria dispar (Lepidoptera: Lymantriidae) (LdMNPV) is a baculovirus capable of causing viral epizootics. LdMNPV must disintegrate in the alkaline midgut, releasing virions that pass through the peritrophic matrix and infect midgut columnar cells. Ingested material has the potential to influence early stages of infection. Host plant induced resistence lead to the increase of phenolic acid and may influence the activity of LdMNPV. In order to evaluate the lethal and sublethal effects of phenolic acids on the spongy moth larvae infected with LdMNPV, artificial diets containing or not containing chlorogenic acid (CH), tannic acid (TA), salicylic acid (SA) and syringic acid (SY) were used to rear the spongy moth larvae inoculated with 92 OBs/μL LdMNPV. The results turned out the lethal effect caused by SYV (SY + LdMNPV) was high. SY played a synergistic effect on LdMNPV against spongy moth larvae assessed by CTF (co-toxicity factor). SA and TA showed an antagonistic effect and CH showed additive effects. Larvae treated by CH, CHV, TA or TAV suffered long duration of the 3rd and the 4th instar and no one survive to the 5th instar stage, inferring that CH and TA inhibited the development of spongy moth larvae. SY, SA, SYV and SAV caused remarkable sublethal effect on spongy moth survivor. Fecundity of the survivor decresed and egg hatching rates were significantly reduced. The hatching rate of SYV was only 46.4 %, about half of CK. Assessing from both the lethal and sublethal effect, SY may be a potential synergist of LdMNPV against spongy moth larvae, improving prevention and control effectiveness of LdMNPV in spongy moth management.