There have been several reports of injury from yellowheaded spruce sawflies in north-central North Dakota this week. All native and introduced species of spruce grown in North Dakota are potential hosts to yellowheaded spruce sawflies. The sawflies are more common in northern North Dakota than in southern areas of the state. These insects are often discovered as late-instar larvae feeding on older needles, at which time much of the damage has been done and chemical control becomes difficult.
Treatments are most effective if they are applied when the larvae are small.
In early spring, tan to straw-yellow adults emerge, mate, and lay eggs in current year's needles at approximately the same time as the young shoots lose their bud caps. Young larvae will begin feeding on new needles and will move to older needles as they mature. Healthy trees will often survive minor needle loss from yellowheaded spruce sawflies, but complete defoliation can kill trees. The first year of defoliation should be taken as a forewarning to monitor and treat, when necessary, for the insect in subsequent years. Although rodents will feed on the cocoons and birds on sawfly larvae and adults, these predators, in addition to various parasites, are not always effective in keeping yellowheaded spruce sawfly populations at acceptable levels.