Web-spinning sawflies

Web-spinning sawflies (Acantholyda) are members of the family Pamphiliidae within the order Hymenoptera. These insects are notorious pests that primarily target coniferous trees, causing significant damage to both commercial timber forests and ornamental landscapes.

The primary hosts for these sawflies include various species of pine, spruce, and larch. Larval feeding can be devastating, as they consume needles rapidly, leading to partial or complete defoliation, which severely stresses the host trees and stunts their annual growth.

The life cycle typically spans one year. The larvae overwinter in the soil within protective earthen chambers or cells. As temperatures rise in spring, they pupate and emerge as adults. After mating, females lay eggs on the needles, where the emerging larvae begin constructing their signature silk webs.

The damage is easily identified by the presence of webbed nests surrounding the needles, which the larvae use for protection while feeding. As they consume the foliage, the needles turn yellow and dry out. If left unmanaged, repeated infestations can eventually lead to the decline and death of the trees.

Management strategies focus on both preventive and curative actions. Cultural practices like soil cultivation around the root zone can disrupt overwintering larvae and reduce populations. For severe infestations, chemical control using approved insecticides applied during the early larval stage is the most reliable method for protecting valuable tree stands.