Abstract
Populations of the apple aphid, Aphis pomi De Geer, on apple were followed from 1959 to 1961, in Northern California. Population trends were generally upwards during early June and downwards through the remainder of the year. In 1959 a second population rise occurred during August. Populations were correlated with growth pattern of the host.Also of importance in the characteristic decline of the apple aphid during July and August are the emigration of alate forms and predator activity. High temperatures were not thought to be an important mortality factor during the early summer months.