Greater horntail wasp (Yellor-horned horntail) - Urocerus gigas (L.)From: Kolk A., Starzyk J. R., 1996: The Atlas of Forest Insect Pests Occurrence: Europe and the northern Asia up to the Altai Mountains. Host plants: Mainly the Norway spruce and common fir, but also the Scots pine, larches and others, occasionally the Sitka spruce and Douglas fir. Morphology: Male adults are 10-30 mm long, and females are 15-40 mm long. The body is elongated, cylindrical. The female is generally yellow, except pronotum and second and fourth segments of the gaster that are black. The gaster is ended with well visible ovipositor. The male has reddish yellow gaster with black base and tip. Antennae of both sexes are filiform and long. Wings are transparent and hyaline. The larva is brownish white with the brownish head and three pairs of very short legs. There is a short, dark spine on the apex of larva's abdomen. Fully developed larva reaches up to 40 mm in length. The pupa is 30-35 mm long, whitish, haired. Biology: U. gigas prefers warm and light site conditions. Adults fly from late-June through August with a culmination in July, particularly in very sunny days. Depending on climatic conditions, this species has one generation per 2-3 years (in unfavorable conditions there might be one generation per 5-6 years). Females lay 2-8 eggs singly, directly into the wood. Each female produces up to 350 eggs. Larvae hatch 15-18 days later and make upward tunnels up to 40 cm long and 0.7 cm wide, packed with wood dust. Before pupation, larvae tunnel to the stem surface, and approx. 1 cm below it they construct pupal chambers of 7-10 x 12-30 mm in size. Larvae overwinter in pupal chambers and pupate in late spring or in summer. Adults emerge through the holes of 4-7mm in diameter. Damage: U. gigas is one of the most dangerous technical pests of conifers, particularly the spruce and fir. It lowers the value of the timber. This species prefers trees exposed to the sun shine. It attacks mainly trees weakened or wounded, standing dead trees, timber and stumps. In stands weakened by industrial pollution it can attack trees with green crowns. Normally this pest infests the lower parts of the stem. Preventive measures: Keeping relatively high density of the stands, and removal of wounded and weakened trees. Insecticide treatment of the stored timber before adult emergence is recommended. Control: Utilization of infested trees, processing and insecticide treatment of infested timber.
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Forest Pests: Insects, Diseases & Other Damage Agents |
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