Small larch sawfly

Systematic position: The small larch sawfly (Pachynematus pumilio) belongs to the order Hymenoptera and the family Tenthredinidae. This insect is a specialist herbivore that has evolved to feed specifically on larch species, posing a recurring challenge in forestry and nurseries.

Host plants: The primary host for this species is the larch (Larix spp.). While adult trees can tolerate some level of defoliation, young saplings and ornamental larch plantings are particularly susceptible to severe damage caused by larval feeding pressure.

Biology and life cycle: The species undergoes a complete metamorphosis. Adult sawflies emerge in the spring or early summer to lay eggs on the needles of host trees. The larvae, which resemble small caterpillars, hatch and feed voraciously on the foliage. After completing their development, they drop to the ground to pupate within protective cocoons in the soil or leaf litter.

Damage and severity: Larval feeding results in skeletonization or complete consumption of larch needles. Heavy infestations lead to significant defoliation, which hampers photosynthesis, reduces growth increments, and can weaken the trees enough to make them susceptible to secondary pests or environmental stress.

Protection measures: Effective management involves an integrated approach focused on both cultural and chemical control. Regular scouting for early signs of defoliation is essential for timely intervention. If monitoring confirms high population levels, the application of selective insecticides can prevent extensive damage. Additionally, cleaning the area around the trees to remove debris can disrupt the pupation cycle of the overwintering larvae.