Pine needle scale

Distribution

Canada

Throughout North America

Micro-habitat(s)

Needle

Damage, symptoms and biology

The pine needle scale is a native insect that attacks pine, spruce, hemlock, yew, and balsam fir. Although not a serious pest of forest trees, it is often abundant on shade and ornamental trees. Dwarf (mugho) pine and blue spruce are especially susceptible to attack and because of the increased use of these species in ornamental plantings, the insect is becoming more widespread.

The insect causes injury to the needles by sucking out the sap. Severe infestations often cause all the foliage except the current year's growth to turn yellow, and trees of low vigour are sometimes killed.

The appearance of waxy, oval white specks or scales (about 3 mm long) on the needles is usually the first indication of attack. When this pest becomes abundant the needles of infested trees look white from a distance. In mid-June, the newly hatched insects (nymphs) emerge from under their scaly protective cover and migrate to other needles to feed. Feeding causes yellowish green spots to appear around each insect. During severe infestations these spots merge, the affected needles dry out and drop prematurely, and some or all of the foliage (except for new needles) takes on a gray, unhealthy appearance. On severely infested pine trees the needles are reduced to half their normal size.

Continuing infestations reduce the vigour and annual growth of trees, making them more susceptible to attack by other insects and diseases and to environmental factors. Severe infestations may eventually kill twigs, branches, or small trees.

There is one generation of pine needle scale each year in the Prairie Provinces. The insects overwinter as eggs beneath the protective covering of the scales. Hatching is highly dependent on temperature; however, most hatching occurs between late June and mid-July. The newly hatched nymphs (crawlers) are minute, oval in shape, and reddish in colour. They wander over the needles searching for suitable feeding sites, and they may be dispersed to nearby trees by the wind. The insects remain stationary during feeding, inserting their mouthparts into needle tissue to feed on cell fluid. Shortly after feeding begins, the nymphs flatten and turn a light brown colour. After this stage the life cycles of males and females differ.

The males develop into a winged form capable of flight. The females, however, remain stationary on the needles for the remainder of their life. Females molt after about 2 weeks to become second-stage nymphs; 3 weeks later (by late July) they molt again to become adults. Males molt after about 2 weeks; each male becomes a tiny winged adult that secretes a white scale covering, about 1.5 mm long. Males emerge from their scale coverings to mate in late July and early August, and then die. During this mating period, the males can frequently be seen hovering in swarms in sunny, protected areas between infested trees. After mating, each adult female secretes a waxy, white scale covering (about 3 mm long), which is completed in mid-August, at which time egg laying begins. As egg laying continues, the bodies of the adult females shrink and eventually die (in September). About 30–50 eggs fill the cavities remaining under the scales and overwinter there.

Other information

Ladybird beetles and tiny parasitic wasps are among the important natural controls for the pine needle scale; extreme heat or heavy rain soon after hatching also destroys many crawlers.

Main host(s)

Austrian pine, balsam fir, bishop's pine, blue spruce, Colorado spruce, common yew, Douglas-fir, eastern white pine, Georgia pine, hemlocks, Himalayan white pine, jack pine, Japanese red pine, Jeffrey pine, limber pine, loblolly pine, lodgepole pine, maritime pine, Monterey pine, mugho pine, pines, pitch pine, ponderosa pine, red pine, Rocky Mountain Douglas-fir, scots pine, shore pine, shortleaf pine, shortleaf pine Pinus echinata Mill. shortleaf pine, spruces, Virginia pine, western white pine, whitebark pine, whitebark pine, whitebark pine