Sirex woodwasp is native to Europe, Asia, and northern Africa. It has
been introduced to New Zealand, Australia, Uruguay, Argentina, Brazil,
Chile, and South Africa as well as Indiana and New York. The most
common method of introduction has been on solid wood packing
material as well as in untreated or dried logs and saw timber. It attacks
a wide variety of pines including Monterey, loblolly, slash and shortleaf.
The female drills into the wood and inserts a toxic mucous and the
fungus Amylostereum areolatum
along with her eggs. 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. The eggs are white, soft, smooth and elongate.
Larvae are creamy white and legless with a distinctive dark spine at the
rear of the abdomen. The frass-filled larval galleries become 'horseshoe'
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 color of the adults. In
July, large round holes are left as adults emerge and begin searching
for new hosts. The adult is a large, robust insect, usually 1 to 1 1/2
inches long. Adult females have dark metallic blue or black bodies
with orange legs. The head and thorax of the males are metallic blue.
The abdomen is orange at the center and black at the base. Sirex
woodwasp is expected to complete one generation per year throughout
most of the United States. 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 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 woodwasp attacks living pines, while native woodwasps
attack only dead, weakened, or dying trees. Read more in the Bugwood Wiki