Adult horntails or woodwasps are 20-35 mm long. Most species have a triangular or spearlike process at the apex of the female abdomen; this process is short in the male. Their body is cylindrical, and they have long slender antennae. Females are large and have a long ovipositor. Adults are mostly black or metallic dark blue, or combinations of black, red, and yellow. Eggs are deposited in the bark of trees and shrubs, and the larvae are wood borers. Larvae are cylindrical, yellowish white, and with a small spine at the posterior end.

Horntails attack both hardwood and softwood trees. A few species have been recorded attacking vigorous trees, but they prefer trees, or parts of trees that have been recently felled, dead, or that are weakened. Larvae may survive in wood that is air-dried and adults emerge after the wood is in use. Small adults emerge from wood that is dried during larval development. Kiln-drying lumber kills larvae. Larval tunnels are 4-8 mm diameter and circular, but they may be exposed longitudinally during sawing ofinfested logs and preparing finished lumber, resulting in an oval shape. The fibrous frass is tightly packed in the tunnels, but it may become loose after drying. Siricids are vectors of phytopathogenic fungi, and their activity can kill and damage trees. Qualitative losses of timber occur from trees that survive attack. An outbreak of Sirex noctilio in the

Pinus radiata forests of New Zealand in late 1940s and establishment of this species in Tasmania and mainland Australia caused considerable economic losses.

The female uses her long ovipositor to penetrate the bark and insert eggs into the cambium to a depth of 10-20 mm. Eggs are laid in batches of about seven and egg-laying is completed in about 14 days. Hatching occurs in 21-28 days, but in Tremex columba, egg hatch is delayed until the following summer; fecundity is 300-400 eggs for large species. Early-stage larvae begin burrowing into the wood at right angles to the oviposition channel. They feed by excavating tunnels in the wood, and use the spine at the end of their abdomen to pack the frass and as support during feeding. After feeding in the outer sapwood, larvae tunnel into the center of the tree, then return to the surface. Cast skins from the three or four immature stages are incorporated into the frass. Pupation occurs at the enlarged end ofa tunnel, about 2 cm from the wood surface; the pupal period is 5-6 weeks. The adult chews a circular hole to emerge. The minimum period for the life cycle is 1 year in warm climate regions, but it may be extended to 2 or 4 years in cold climate regions.

Adults generally emerge in late summer and early fall. Adults fly in sunshine, and make a buzz like bees. Mating takes place in treetops, which is where the male bees usually remain; females descend to low levels to lay eggs. Females are facultatively parthenogenetic, and many oviposit before mating. T. columba deposits about half of its eggs in the frass in its gallery before emergence. These unfertilized eggs produce males, some hatching in the fall, others the nextspring. Mated females produce offspring of both sexes.

Horntail larvae are parasitized by several species of ichneumon wasps (Ichneumonidae) of the genera Megarhyssa and Rhyssa. Megarhyssa atrata lineata, M. greenei greenei, and M. macu-rus lunato have ovipositors thatare 35-40 mm long and longer. The female wasp inserts the ovipositor through the bark and deep into the wood to deposit eggs on or near horntail larvae or pupae in their galleries. The female parasite first punctures the beetle larva with her ovipositor; she then deposits an egg close to the potential host. The larva of Rhyssa feeds externally on its host. The life cycle of the parasite is completed in 1 year.

Symbiotic fungi are utilized as food by siricid larvae. The larvae do not ingest wood, but they extract necessary nutrients from the fungal mycelium, which grows in the tunnels, and is digested by their salivary secretions. The fragments of wood removed by the larval mouthparts are passed along the outside of the body and packed in the tunnel behind them.

During oviposition, the female deposits a small amount of fungal spores with each egg, and the mycelia that develop from these spores provide food for the developing larva. The fungus associated with siricids is often species-dependent, and includes species of Amylostereum and Daedalea.

Western horntail, Sirex areolatus (= S. apicalis) Adult females are 24-35 mm long, dark metallic blue; the wings are dark. Males are 18-24 mm long, and the abdominal segments 3-7 and sometimes the front tibia and tarsi are dark red to reddish brown (and known as S. apicalis). This species attacks dead Monterey cypress, and other cypress trees, and it is known to infest redwood lumber in storage. This species occurs from New Mexico north to Washington in the USA, and British Columbia.

Blue horntails, Sirex californicus, S. cyaneus, S. edwardsii, S. juvencus, S. nigricornis, S. obsus Adults are 23-30 mm long, the body is usually dark metallic blue to black, and the wings are clear to completely dark. The legs, except the coxae, are red or yellow. The ovipositor extends 10-15 mm beyond the tip of the female abdomen. Larvae are 20-30 mm long and yellowish white; the head is dark yellow to yellowish brown, and the legs are small. The larvae of these species attack a variety ofconiferous trees, including pine (pitch and shortleafpine), fir, spruce, and Douglas fir. They occur in eastern Canada, and in northeastern and midwestern USA. S. californicus occurs in California, Oregon, Washington, and British Columbia, and has been reported from New Mexico.

Long-tailed horntail, Sirex longicauda Adult females are about 40 mm long, and the body is dark metallic blue. Males are about 25 mm; the abdominal segments 3-7, and the tibiae and tarsi of the front and midlegs are reddish brown. This species may be restricted to California; it is commonly found indoors.

Sirex wasp, Sirex noctilio Adult females are about 25 mm long and metallic blue. Males are about 18 mm long, metallic blue, and have a dark-orange abdomen. The emergence hole in the wood is 5-6 mm diameter. This species attacks Pinus spp. trees, and often causes the death of the tree. Itprefers to oviposit in Pinus radiata trees that have wide annual rings; these trees typically have a small amount of heartwood. Larvae complete development in 1 or 2 years and have 7-8 larval instars. It is known from the Eurasian region, Canada, and South Africa. It was introduced into New Zealand and Australia.

Pigeon tremex, Tremex columba (Fig. 9.1c) The adult female is 37-50 mm long. The head, antennae, and thorax are reddish brown to black; the abdomen is black with yellow bands and spots along the sides. The wings are about 50 mm long, and light brown. Males are 18-37 mm long, and the body is reddish brown with some black markings. Antennae are slightly swollen in the middle, and are as long as the head and thorax combined. Eggs are laid singly at depths of 10-12 mm in the wood. Full-grown larvae are about 50 mm long, and yellowish white. The end of the abdomen has a sclerotized process that has two pairs of small teeth. This species attacks beech, maple, birch, elm, hickory, sycamore, and oak. It occurs throughout northern North America, but a subspecies has been reported from elm timber imported into New Zealand. A related species, Tremex juscicornis, occurs in Europe and Asia.

White-horned horntail, Urocerus albicornis (= Sirex abdom-inalis) Adult females are 25-30 mm long, and the body is bluish black to black; wings are dusky. The middle of the antennae, the cheeks on the head, and the bases of the tibiae and tarsi are white; and white spots may occur on the abdomen. Males have abdominal segments 3-6 yellow, and the wings are clear. This species attacks many species of coniferous trees and occurs throughout northern North America. It may attack freshly sawn lumber.

Yellow-horned horntail, Urocerus flavicornis (= Sirex bizona-tus, Urocerus riparius) Adults are 22-33 mm long, and the body is black. The antennae, tibiae, and abdominal segments 1, 2, 7, and 8 are yellow or reddish yellow. Wings are clear or slightly yellowish at the bases. The males have abdominal segments 3-6 yellow and the wings are clear. This species breeds in pine, fir, Douglas fir, and other coniferous trees. It occurs throughout northern North America.

Wood wasp, Urocerus gigas (Fig. 9.1 b) Adults are 18-35 mm long, the body is bluish black, and there is a yellow patch below each eye. Larvae are about30 mm long, yellowish white, and the spine at the posterior end is dark brown. This species attacks a variety of coniferous trees. It occurs in the UK and Europe. The ichneumonid, Rhyssa persuasoria, is a larval parasite of the larvae.

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