Abstract
Field, glasshouse, and laboratory tests showed that deposits of polyhedra of the nuclear polyhedrosis virus of the cabbage looper, Trichoplusia ni (Hübner), on foliage are practically non-infective after a 1-month exposure to weathering. Inactivation by sunlight appeared to be more important than removal by washing by rain in causing this loss of activity. The virus was readily inactivated by exposure to ultraviolet light. Virus exposed in aqueous suspensions of polyhedra or in wetted deposits was inactivated by shorter exposures than was virus in dry deposits of polyhedra.