Observations on the biology and population dynamics of Cinara ponderosae Williams) in the westside Sierra Nevada forests of California are presented.

The species is believed to be anholocyclic, because sexuales, eggs, and fundatrices were absent. In the spring following winter survival on ponderosa pine (Pinus ponderosa Lawson) in the foothills, populations migrated up the west slope of the Sierra Nevada. The local population in Blodgett Forest, Eldorado County, began in May with the number of aphids and colonies expanding throughout June and collapsing by the end of July. Detailed study of instar distribution, based on a sampling every four days, showed a gradual increase in older instars until population collapse. First generation 4th instars and apt era e moved throughout the tree and began new colonies.

Predators, primary and secondary parasites, and ant associates were noted and discussed.