none A. areolatus parasitized the 1st and 3rd generations of P. californiensis and produced two generations in spring. Though the aphid infests maple trees all the year round, winged females appear several times in a year and produce larvae on the trees which provide a large amount of suitable feeding sites. When the winged females reached the trees and produced larvae, the wasps which emerged on other trees also came and parasitized the larvae intensely. The number of mummies in the 2nd generation correlated with the number of mummies in the 1st generation of the same year and the aphid density, and increased with increasing aphid density. Some aphids escaped from parasitism and deposited aestivating dimorphs which never became parasitized. This parasitoid was one of the important mortality factors of the aphids during the years covering the study. However the mortality of the aphid population was inversely proportional to the density. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology Aphidius areolatus (Braconidae); Hemipteran hosts; Periphyllus californiensis; Host parasite population relationships; Host parasite relationships; Population interactions with Periphyllus californiensis (Hemiptera); Population dynamics; Interactions with hemipteran host Periphyllus californiensis (Aphidoidea); Hymenopteran parasites; Aphidius areolatus; Host parasite population relationships; Host parasite relationships; Population interactions with Aphidius areolatus (Hymenoptera); Population dynamics; Hymenopteran parasitism relationships