Rainfall effects on transmission of gypsy moth (Lepidoptera: Lymantriidae) nuclear polyhedrosis virus

We explored the action of rain on the translocation of the gypsy moth nuclear polyhedrosis virus (LdNPV) at tree, branch, and leaf level. Artificial rainfall was used to simulate naturally occurring rainfall on leaves contaminated with 1st-instar gypsy, moths, Lamantria dispar (L.), which had died of LdNPV. Bioassays using larvae in mesh bags on originally contaminated branches and branches below indicated that rainfall is effective in moving virus from branch to branch. This result was confirmed by an experiment using similar methods and naturally occurring rainfall. To examine this effect at the level of the leaf, we bioassayed leaf disks extracted from leaves with and without cadavers. Mortality of test larvae in leaf disk bioassays was strongly correlated with the presence of a cadaver on a leaf, but not confined to disks with cadavers. Mortality caused by non-LdNPV factors was also associated with consumption of a cadaver