Xylococculus macrocarpae (Coleman) had one generation a year on incense cedar (Calocedrus decurrens (Torr.) Florin) at Blodgett Forest, El Dorado County, California, at 1200 to 1550 m elevation. There were four female stages and five male stages. On small incense cedar, adult females laid eggs on the foliage in spring. Crawlers then settled on branches and middle and upper boles, where they molted to legless stages in summer. Females overwintered as legless second and third stages, and males as legless second stages and legged prepupae. In spring, male prepupae and pupae migrated lower on the bole while female adults moved to the foliage.

X. macrocarpae was the most common prey under incense cedar bark during the winter months when insectivorous birds forage on the tree; the insect was especially abundant on branches and the upper and middle boles. Two hymenopterous parasitoids were reared from X. macrocarpae, the previously undescribed Parechtrodryinus xylococculi Beardsley and Gordh (Encyrtidae), and Mesopolobus sp. (Pteromalidae). The trogositid beetle Eronyxa expansus Van Dyke was a common predator, possibly restricted to the scales.