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Sirex noctilio (Lesser Horntail Wasp) is a species of woodwasp.
Areas of Origin
It is native to Europe, Asia, and northern Africa, and has been introduced accidentally to New Zealand, Australia, Uruguay, Argentina, Brazil, Chile, South Africa, Zimbabwe, and most recently (since 2005) eastern Canada and the northeastern United States.
The white, soft, smooth and elongate eggs are oviposited by the female into the wood.
The creamy white and legless larvae have a distinctive dark spine at the rear of the abdomen.
Although initially creamy-white, the pupae gradually assume the colour of the adults.
The adult is a large, robust insect, 10-32 mm long. Adult females have dark metallic blue or black bodies with orange legs. The males' head and thorax are metallic blue, and the abdomen is orange at the center and black at the base.
The female drills into the wood and inserts a toxic mucous in addition to the fungus Amylostereum areolatum. The mucus prevents anti-fungal toxins from being formed at the site of infection. The fungus grows in the wood causing it to dry out and the trees die in a few weeks or months. At the same time, the female also deposits white, soft, smooth and elongate eggs into the wood. Larvae are creamy white and legless with a distinctive dark spine at the rear of the abdomen. The frass-filled larval galleries become 'horse-shoe' or 'u-shaped' as the larvae tunnel towards the heartwood, but then turn back towards the sapwood. Larvae feed on the fungus, which has converted the wood cellulose into a more easily digestible form. The pupae formed in the outer layers of the sapwood are initially creamy-white and gradually assume the colour of the adults.
In summer, large round holes are left as adults emerge and begin searching for new hosts. It completes one generation per year in warmer region, or per two years in colder regions. The most important symptom is the progressive and irreversible chlorosis in the crown, followed by a sudden wilting of the foliage, heavy needle fall, and finally death and decay. Initially it is important to inspect the surfaces of the stems for resin drops released after eggs are laid. Narrow bands of brownish fungal stain in the outer sapwood can be noted in infested trees. In general, Sirex woodwasps attacks living pines, while other woodwasps attack only dead, weakened, or dying trees.
This insect is easily transported in solid wood packing material as well as in untreated or dried logs and saw timber.
- Kolk A., & Starzyk J. R. (1996): The Atlas of Forest Insect Pests (Atlas skodliwych owadów lesnych), Multico Warszawa.
- Ontario Ministry of Natural Resources Information Centre
- Global Invasive Species Team