Alder sawfly

The alder sawfly (Pristiphora alnivora) belongs to the order Hymenoptera and the family Tenthredinidae. This insect is a significant pest specialized in feeding on various alder species. It is commonly found in both natural forests and landscape plantings, where it can cause notable aesthetic and health decline to the host trees.

The host plants primarily affected by this sawfly are trees within the genus Alnus. The female sawfly deposits eggs into the leaf tissue, and the emerging larvae begin to consume the foliage. In cases of outbreaks, the feeding activity is severe enough to strip the tree branches of their leaves, significantly reducing the tree's health.

The biological cycle of this species follows a standard sequence: egg, larva, pupa, and adult. The insect typically undergoes winter diapause in the soil or leaf litter beneath the host tree, remaining in a cocoon stage. When environmental conditions improve in the spring, the pupation process is completed, and adults emerge to restart the life cycle.

Damage caused by Pristiphora alnivora involves heavy skeletonization or complete defoliation of leaves, leaving only the primary veins. This intensive feeding reduces the photosynthetic surface, weakening the tree's overall vigor. Over several seasons, repeated infestations can lead to canopy dieback and increased vulnerability to other stressors, such as fungal diseases.

Effective management and protection strategies are essential for maintaining the health of alder populations. Recommended control measures include:

• Conducting regular inspections of foliage during spring and early summer.
• Cultivating the soil under trees to disrupt the overwintering pupae.
• Utilizing biological insecticides like B.t. (Bacillus thuringiensis) to target young larvae.
• Applying systemic or contact chemical insecticides when larval populations reach damaging thresholds.