Web-spinning sawfly

Systematic position: The web-spinning sawfly (Cephalcia arvensis) belongs to the order Hymenoptera, family Pamphiliidae. It is a notorious defoliator known for causing severe damage to coniferous trees, particularly in forestry and ornamental landscapes.

Host plants: The primary host of this pest is the Norway spruce (Picea abies). In cases of large-scale infestations, the insect is capable of defoliating vast areas, leading to significant physiological stress and tree mortality.

Biology and life cycle: Adult sawflies emerge in the spring. Females lay eggs on needles. Upon hatching, the larvae construct web-like nests made of silk threads around the branches. They live and feed inside these protected structures throughout their developmental stage.

Damage and harmfulness: The larvae consume needles, often stripping branches entirely. The presence of the pest is signaled by the accumulation of frass and brown, dried-out needles trapped within the conspicuous silken webs. Heavily infested trees may lose their foliage, which stunts growth and increases vulnerability to secondary pathogens.

Control measures: Management strategies focus on early detection of web nests and the application of chemical or biological insecticides. Maintaining a healthy stand through proper forest management is key to preventing outbreaks.

• Application of systemic insecticides during the early larval stage.
• Manual removal of webs from young or specimen trees.
• Conservation of natural predators such as parasitic wasps.
• Monitoring adult population levels with pheromone traps.