Methods of Recording Aphid (Homoptera: Aphididae) Populations on Potatoes and the Distribution of Species on the Plant

Abstract

In Eastern Canada, aphids cause serious losses in the potato crop–directly by injuring heavily infested plants and indirectly as vectors of viruses. A field study of factors affecting populations of potato aphids necessitates a method of estimating population that allows comparisons of results from different varieties of potato and from potatoes grown under different conditions. Davies (1934) described one of the first methods of estimating aphid populations in the field; he counted the aphids on lower leaves chosen at random, and expressed the opulation as aphids per 100 leaves. Simpson (1940) reported that the species of aphids on potatoes in Maine differed in their distribution on the plant; to obtain a better estimate of the population, he modified Davies' method and counted the aphids on equal numbers of leaves selected at random from the top, middle, and bottom portions of the plants. Other workers (Joyce, 1938; Hansen, 1941; Whitehead, 1943; Thomas and Jacob, 1943; Staniland, 1943; Jacob, 1944; Doncaster ana Gregory, 1948; Münster, 1948) used various methods of selecting leaves for the sample but continued to express the population as aphids per 100 leaves. Much of the earlier work was in the form of surveys to determine the population of aphids above which the maintenance of healthy seed stock was not a practical proposition.