Effect of dew from cotton and soybean foliage on activity of Heliothis nuclear polyhedrosis virus

The ionic composition of dew collected from foliage of cotton and soybean plants as well as its potential for inactivation of Heliothis NPV were compared. Cotton dew had a mean pH of 8.8 and was more alkaline than soybean dew (pH 7.8). Cotton dew had a higher concentration of ions that did soybean dew but there was no qualitative difference in the cation content of dew from the two hosts. In bioassay tests, no loss of activity occurred when polyhedra were held in dew of either plant species. If the dew in which polyhedra were suspended was air-dried and resuspended daily in deionized water, polyhedra in soybean dew remained active but in cotton dew retained little activity after 7 days. Also, electron microscopical examination of polyhedra pelleted from these cotton dew preparations showed much dissolution after 7 days. Although there was dissolution of polyhedra in cotton dew when dried, an examination of polyhedra on the upper surface of either plant species in the field showed little degradation after 7 days.