Abstract: The experiments in 1984 and 1985 showed that physical factors such as temperature ultraviolet light sunlight and pH of the buffer can influence the infectious ability of the Acr NPV.The infectious ability of the Acr NPV does not vary whether it is stored in a refrigerator at 4? for 14 months and 28 months or in an infected body that stayed on a tree trunk in an orchard for 14 months.The infectious ability of the Acr NPV treated at 35? decreases in relation to the length of treatment. The Acr NPV can be damaged seriously by ultraviolet light and lost its infection ability entirely when it is irradiated for 240 minutes with ultraviolet rays.Experiments in the orchard show that the infectious ability is different when the Acr NPV suspension is sprayed on the faces and the backs of the leaves.The infectious ability of the Acr NPV is related to the pH of a phospha-tic buffer. The infected larvae fall ill slowly when the pH is at 3. 5 or at 10-5 and fall fast when at 7. 2.

Key words: Acr NPV (Nuclear Polynedrosis Virus of Aporia crataegi), Infectious ability, Physical factors influence