Larch sawfly

The larch sawfly (Pristiphora laricis) is a destructive pest belonging to the order Hymenoptera and the family Tenthredinidae. This insect is a specialist that primarily affects larch trees, causing concern for forestry professionals and owners of ornamental coniferous landscapes.

The main host plants are various species of Larix. By focusing its feeding activity on young needles, the larch sawfly can cause significant physiological stress to the tree, impacting its photosynthesis, overall growth rate, and vigor if the infestation is repeated over several consecutive years.

The biological cycle is synchronized with the growth of the host tree. Adult sawflies emerge in the spring, and females deposit eggs into slits made in the newly developed needles. The larvae, often resembling caterpillars, feed voraciously throughout the summer months before descending to the soil to pupate in protective cocoons.

Feeding damage is characterized by needle loss starting from the top of the crown. When populations are high, defoliation can be extensive, giving the trees a sparse and unhealthy appearance. While a single season of defoliation may not kill a healthy tree, repeated attacks significantly weaken the tree, making it susceptible to secondary environmental stresses.

Effective management requires a combination of monitoring and intervention strategies. IPM (Integrated Pest Management) tactics are highly recommended to keep populations below economic injury levels:

• Regular monitoring of needle development and larval stages in early summer.
• Application of selective systemic insecticides when larval population thresholds are exceeded.
• Enhancement of natural predator populations, such as birds and parasitic wasps, to ensure biological control in the forest ecosystem.