Sirex juvencus

Steely-blue wood wasp

Description

Sirex juvencus, commonly known as the steely-blue wood wasp, is a large horntail found across Europe, Siberia, Japan, and other regions. The adults display sexual dimorphism, with females being slightly larger (up to 32 mm) and having a metallic bluish-black body, while males are slightly smaller and darker. The females use their ovipositor to lay eggs deep into the wood of weakened or dying coniferous trees, especially spruce and pine. As larvae hatch, they burrow into the wood, creating extensive tunnels. Additionally, S. juvencus carries a symbiotic fungus that infects the wood, which aids in larval development by breaking down the wood fibers, making it easier for the larvae to digest.

Symptom

Infestation is possible by small, round exit holes (4-6 mm). In the wood, there are tunnels densely filled with frass. In adult S. juvencus, the female’s ovipositor is short, shorter than the body. Males have several yellow segments on the abdomen. While the female has all legs red, the male has the front two pairs of legs red and the hind pair black.

Tree Species: Pine, Fir, Spruce, Larch

Part of a plant- attacked: Tree trunk, Branch

Pest significance: Harmful

Pest Category: Insects

Present in EU: Yes