The effect of foliage damage on transmission of gypsy moth nuclear polyhedrosis virus

Results of published studies suggest that gypsy moth defoliation may cause elevated tannin levels in trees, which in turn results in reduced larvae mortality caused by the nuclearpolyhedrosis virus (NPV). In a series of field experiments, we tested the hypothesis that gypsy moth defoliation of oaks leads to reduced virus transmission rates. In each of three years; we measured virus transmission rates in gypsy moths feeding on oaks, and tannin levels in oak leaves, with and without experimental defoliation in oak forests with almost no naturally-occurring gypsy moths or virus. In our experiments, we found that there was no effect of gypsy moth defoliation on tannin levels, and consequently virus transmission both in the field and in the lab was unaffected by defoliation. Our results suggest that gypsy moth defoliation does not affect tannin levels early enough in the larval season to have a measurable effect on the interaction between gypsy moth and its nuclear polyhedrosis virus.