Adelgids—Adelges and Pineus spp.
Adelgids (family Adelgidae) are aphidlike insects that suck plant juices from conifers. At least eight species occur in California. Hosts include Douglas-fir, fir, hemlock, larch, pine, and spruce.
Adelgids commonly occur beneath cottony white or grayish wax they secrete or inside of galled plant tissue. The adelgids themselves are small, dark, soft-bodied, oval insects. The insects can look different depending on the host, and several different-looking stages of the same species can occur together.
Balsam woolly adelgid. Adelges piceae has seriously damaged or killed tens of thousands of true fir trees in the eastern United States. Inadvertently introduced from Europe, it more recently has become established in Oregon and northwestern California. This adelgid occurs only on Abies species and does not alternate hosts in the United States.
The round, dark purple to black adelgids are 1⁄25 inch long or less. They occur under cottony wax on fir twigs and trunk bark. When infested, shoots become stunted and develop globular galled wood (gouting) around buds and branch nodes. Infested shoots and limbs die back and the firs gradually decline and commonly die.
If you find an adelgid-infested dying fir or suspected balsam woolly adelgids, report the location to the local office of the county agricultural commissioner. For more information see Balsam Woolly Adelgid from Utah State University.
Cooley spruce gall adelgid. Adelges cooleyi feeds on spruce and Douglas-fir and some populations alternate generations between these hosts. Nymphs produce a white, cottony tuft where each individual settles and feeds on cones, needles, and shoots. High populations cause needles to become distorted, spotted, and drop prematurely.
Cooley spruce gall adelgid feeding can cause spruce terminals to distort into a gall that eventually encloses a group of the insects. The galls are 1/2 to 3 inches long and light green to purple. About midsummer, the nymphs emerge from galls and molt into winged adults. The empty galls harden, turn brown, and die and may persist for years.
Cooley spruce gall adelgid produces galls on spruce only when Douglas-fir is nearby because this alternate host is the source of the adelgid’s gall-forming stage. Galls in California are mostly seen along the North Coast and in mountainous areas where Douglas-fir is common. For more information and an illustration of its host-alternating life cycle, see Cooley Spruce Galls from Colorado State University.
Pine bark adelgids. The pine bark adelgid (Pineus strobi), also called the pine bark aphid, and the pine leaf adelgid (Pineus pinifoliae) produce abundant pale wax where they feed on pine bark and twigs. Some populations migrate between pine and spruce. On spruce twigs infested by Pineus species galls form and are typically smaller and less prominent than the galls of Cooley spruce gall adelgid.
Adult female Pineus species are dark blue to purplish black, soft-bodied insects that lay yellowish pink eggs in cottony, wax-covered masses. The mobile first instars (crawlers) that emerge resemble tiny pepper grains on the cottony egg masses. Settled nymphs (immatures) are brown, dark blue, or greenish and occur under wax.
Adelgids develop through three life stages: egg, nymph, and adult. Most adelgids have several generations per year and a complex life history that can include several types of adults with differing appearance. Their biology can include generations alternating between two different conifer species.
Adelgids suck and feed on conifers and inject saliva that can cause host tissue to distort. Adelges and Pineus species cause white cottony tufts on the bark, branches, cones, needles, or twigs. Heavily infested trees may seem covered with snow. Cone-shaped galls or swollen twigs may develop on infested fir and spruce.
High adelgid populations cause foliage yellowing, early drop of needles, and drooping and dieback of terminals. Prolonged high populations can retard plant growth.
Vigorous plants tolerate moderate populations and most adelgid species are unlikely to seriously harm trees. Exceptions are balsam woolly adelgid introduced in Northern California and hemlock woolly adelgid in the eastern United States. Be alert for these serious pests and any unusually damaging adelgid problems on hemlock, true fir, or spruce. If suspected balsam woolly adelgids or hemlock woolly adelgids are found where not known to occur report the location the local office of the county agricultural commissioner.
Usually no control is needed to protect the health of established trees. An exception is the balsam woolly adelgid. See the balsam woolly adelgid section in Managing Insects and Diseases of Oregon Conifers (PDF) from Oregon State University for strategies to control this pest.
Predators of adelgids are especially important in natural forests, where most adelgids are uncommon. Adelgid predators include brown lacewings, green lacewings, the small maggotlike larvae of aphid flies and predaceous midges, and adults and larvae of several species of small lady beetles.
Replace some spruce with other species to reduce adelgid populations that alternate hosts. A forceful stream of water directed at the cottony masses on conifers, especially on trunks, dislodges and kills many adelgids.
On spruce, to restore the plant’s aesthetic quality and provide some control, break off or clip and dispose of infested foliage when the galls are green and before the insects have emerged. Avoid excess fertilization and quick-release fertilizers, which can promote adelgid abundance.
High adelgid populations, especially on young trees, can be controlled by applying horticultural or narrow-range oil, insecticidal soap (potassium salts of fatty acids), or certain other insecticides in the spring when crawlers are abundant. Be aware that oil spray may remove the desirable bluish color from foliage of certain conifers (e.g., blue spruce), but this does not affect tree health. Avoid residual, broad-spectrum insecticides (e.g., carbaryl and pyrethroids), which can cause an increase in spider mite populations unless a miticide is added. Insecticide sprays are more effective when a wetting agent is added and applications are made with high-pressure equipment so that the spray penetrates the insects’ waxy secretions. Certain systemic insecticides (e.g., imidacloprid) can be effective.
Insecticide sprays are not effective in preventing galls unless application is correctly timed based on careful and frequent monitoring. Examine the base of terminal buds on spruce and locate the overwintering females. Inspect females regularly during late winter and spring to determine when they begin to increase greatly in size and start to produce waxy strands; at this time thorough spraying with insecticide can provide control.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM) and Western Forest Insects (PDF) from the USDA Forest Service.