Foreign Predator Introductions for Control of the Balsam Woolly Aphid in the Pacific Northwest

Abstract

The balsam woolly aphid, Adelges piceae (Ratzeburg), an import from Europe, causes major damage to true fir forests in North America. A program has been underway since 1957 to control the pest in Oregon and Washington by introducing insect predators. Twenty-three species have been introduced from 7 countries throughout the world. They include 15 species of beetles, 4 of flies, 3 of lacewings, and 1 bug. Three species of flies, Aphidoletes thompsoni Möhn, Cremifania nigrocellulata Czerny, and Leucopis obscura Haliday and 2 species of beetles, Laricobius erichsonii Rosenhauer and Pullus impexus (Mulsant), are successfully established. They prey on the aphid but so far have not sufficiently reduced populations to prevent tree killing. Reasons for their failure include poor synchronization of predator-prey seasonal habits, inadequate searching ability of the predators, and inability of the host trees to withstand even light populations of the aphid. Search for more effective predators is continuing. The aphid problem is expected to decrease as the present virgin old forests are converted, under management, to less susceptible young forests. Aphid predators may become relatively more effective under such forest conditions.