抄録
In order to know the interrelation between the infection of potato virus disease and the seasonal variation of aphid population, investigations were carried out on the Chugoku branch farm in three successive years from 1946 to 1948. The results of the study are summarized as follows:- 1. In Himeji district, the peach aphid (Myzus persicae Sulzer) and Cotton aphid (Aphis gossypii Glover) are the main species attacking the potato. As to the ecological type, apeterous female predominated in all three years, throughout the potato season. 2. The infestation of aphids on potato plants generally began at about the end of April, just after the potato sprouted ; a month later, at about blossoming time of potatoes it reached the maximum, and at about the middle of June, it terminated. In the fall crop, the infestation began early in October and ended by the end of the 10th of December, and generally speaking more aphids were observed on potatoes in fall than in spring. Some differences, however, were observed during the three years. These appeared to be due mainly to the difference in growth as a result of growing conditions. 3. The rate of increase in virus infection is closely connected with the number of aphids. It was also confirmed that from 20 to 30 days were necessary for the virus poison introduced by viruliferous aphids to be translocated from leaves to tubers. 4. The above mentioned fact offers the foundation in determining the date of harvesting in order to secure disease free seed tubers in the warmer region ; i.e. if seed potatoes were dug up in spring within some 20 days after the maximum infestation of aphids, we can safely say that they are practically virus free. 5. In fall crop, notwithstanding the more infestation of aphids than in spring, there was no significant increase of virsu, indicating the importance of fall crop for the production of seed potatoes.
