Pine sawfly

Systematic position: The pine sawfly (genus Diprion) belongs to the order Hymenoptera and the family Diprionidae. These insects are significant defoliators that impact coniferous forests and nurseries globally.

Host plants: The primary hosts for these sawflies are pine species (Pinus spp.). They are particularly devastating to Scots pine (Pinus sylvestris) stands, affecting trees of varying ages from young saplings to mature timber.

Biology and lifecycle: The lifecycle usually involves one or more generations per year depending on the climate. Adult females utilize a saw-like ovipositor to insert eggs into pine needles. After hatching, the larvae, which resemble caterpillars, feed gregariously on the needles before spinning silk cocoons to pupate in the soil or on bark.

Damage and economic impact: The feeding larvae consume the needles, causing severe defoliation. A heavy infestation can leave branches completely bare, causing tree stress, stunted growth, and increased susceptibility to secondary pathogens or wood-boring insects, which often leads to tree mortality.

Control measures: Integrated pest management is key to controlling Diprion populations. This includes maintaining diverse forest ecosystems to support natural predators like birds and parasitic wasps. Chemical control using registered insecticides is often required during outbreaks, while biological controls, such as nuclear polyhedrosis viruses, offer a sustainable alternative for large-scale forest management.