Factors Affecting the Infestation or Aphids on Potato Plants

Abstract

This paper deals with the results of a study on the farm of Utsunomiya University for two years, i.e., in the summer of 1964 and 1966,concerning the living sites of aphid species on potato plants, infestation and its major causes. Myzus persicae SULZER, Aulacorthum solani KALTBNBACH and Macrosiphum euphorbiae TROMAS were found in large numbers on middle-mature leaves and upper-immature leaves, while Aphis gossypii GLOVER was found on the reverse side of middle-mature leaves and lower-old leaves. With regard to M. persicae, the number of individuals was noted to reduce immediately after blossoming, presumably because of the increase in number of natural enemies, mainly parasitic Hymenoptera. As regards A. gossypii, the intensity of infestation fell within a certain period, followed by a peak in number of the insects, irrespective of the growing age of the plant, even when sowing was carried out at different times. For this reason, the reduction in number of A. gossypii is ascribable not to natural enemies nor some factors in the plant, but to some meteorological factors, such as high temperature and rainfall. That M. persicae is more intensely affected by natural enemies than A gossypii, may be explained by the fact that M. persicae livers on the upper and middle leaves where the density of natural enemies is higher.