A bioassay technique was used to estimate the concentrations of infectious gypsy moth nucleopolyhedrosis virus (NPV) that occur naturaIly in leaf, bark, litter, and soil samples taken from woodland plots in Connecticut and Pennsylvania. These concentrations were then compared to those in samples taken sequentially after treatment of these plots with NPV. Results indicated that NPV is a natural component of the host's habitat, persisting in high concentrations in soil, litter, and on bark for at least one year after natural epizootics. Activity of NPV in spray deposits on foliage and bark was measurable for only 3-15 days after NPV treatment, whereas activity of NPV liberated from larval cadavers onto bark was measurable in high concentrations through May of the year foIlowing treatment. The application of NPV at the rate of 2.5 x 10 12 polyhedral inclusion bodies (PIB)/ha to an area already containing high concentrations of naturally occurring NPV did not cause an increase in the environmental NPV load. Although the application of NPV at the rate of 5 x 10 12 PIB/ha to plots containing low natural concentrations of NPV resulted in measurable increases in the NPV load in these plots, these increases were not, overaIl' significantly higher than those occurring in a control plot that was not treated with NPV.

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