Birch sawfly

The Birch sawfly (Craesus latitarsus) is a specialized insect pest belonging to the order Hymenoptera and the family Tenthredinidae. This species is known for its selective feeding habits, primarily targeting birch trees. It is recognized as a significant defoliator in both forestry and ornamental landscapes, capable of causing localized outbreaks.

Host plants include various species of birch. The larvae, often referred to as false caterpillars, emerge from eggs laid in the leaf tissue and begin feeding immediately. Because they exhibit gregarious behavior, feeding in large groups, they can strip entire branches of foliage, leading to rapid defoliation and stressing the affected tree significantly.

The biological cycle of this pest involves overwintering as mature larvae within tough, papery cocoons hidden in the soil beneath the host tree. Adult sawflies emerge in the spring to mate and lay eggs. Depending on the environmental conditions, the pest may produce one or two generations per year, with larval activity peaking during the warm summer months.

Symptoms of infestation are easily identified by the presence of larvae along the leaf margins, often assuming an S-shaped posture when disturbed. The damage manifests as skeletonized leaves, eventually leaving only the midribs and major veins. Severe infestations can cause premature leaf drop, stunted growth, and a reduction in the overall vigor of the tree, making it susceptible to secondary stressors.

Effective management strategies require a combination of monitoring and intervention. Key measures include:

• Manual removal of larval colonies during the early stages of infestation.
• Encouraging natural predators and parasitoids that help regulate sawfly populations.
• Application of selective insecticides during the early larval stages when they are most vulnerable.
• Maintenance of the area beneath the canopy, such as soil cultivation, to disrupt the overwintering pupal stage.