Density and survivorship of solitary and coexisting populations ofPineus boerneriAnnand andPineus coloradensis(Gillette) (Homoptera: Adelgidae) were studied for 3 years in 12 stands of red pine,Pinus resinosaAiton, in Connecticut and Rhode Island. Survival ofP. boerneriwas higher on branches than on needles during winter but higher on needles than on branches during spring and summer. Survival ofP. coloradensiswas always higher on needles than on bark. The percentage of branches that were resinous (indicative of injury) increased at four coinfested pine stands from 1980 to 1982. The proportion of theP. boerneripopulation on needles relative to bark increased during that period; the opposite trend was observed forP. coloradensis. Decreasing density ofP. coloradensison needles was related to increasing density ofP. boerneri, and was due to a combination of greater mortality on needles and greater colonization of bark, where chance for survival was even less.P. boerneriestablished and maintained numerical dominance overP. coloradensisin these four coinhabited pine stands and on pine seedlings in the greenhouse.