Forest Pests: Insects, Diseases & Other Damage Agents

The pine leaf adelgid is an aphid-like insect found throughout the range of white pine. It forms harmless cone-like galls on red and black spruce, which are alternate hosts. White pine is injured in alternate years; light infestations do little harm, but continued heavy attacks can cause mortality. Trees that survive heavy attacks are usually deformed.

There are four and sometimes five stages in the 2-year life cycle of this adelgid. On spruce, the insects are tiny and hidden under bud scales or within the galls. On white pine they are more readily seen. In June of odd-numbered years, the winged adults fly from spruce to white pine, where they lay eggs on the old needles, then die. Wingless nymphs emerge from these eggs, crawl to the axes of newly expanding shoots, insert their mouthparts and begin feeding. The nymphs mature in May of even-numbered years, then fly back to spruce trees where they lay eggs. The eggs on spruce trees hatch in June and the nymphs feed on sap from spruce needles. When mature, this form of the adelgid mates. The eggs produce the insects that hibernate under spruce bud scales.

Natural factors usually keep pine leaf adelgid populations under control.Many individuals are lost during migration to pine and back to spruce. Hover fly maggots and soldier beetles destroy many of the eggs laid on white pine. Because the adelgids stay in groups, they may attack only a few shoots of a white pine trees. If there are too many insects on a shoot, they may all starve because they cannot move to another shoot.

Adult(s); winged adult with reddish eggs under wings can be found on previous year's needles E. Bradford Walker, Vermont Department of Forests, Parks and Recreation

Damage; feeding results in flagged lateral shoot tips that begin to appear in mid-summer Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation

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