AppearanceBody length 5-11 mm; primary color is black; 3rd to 6th abdominal segments have yellow transversal bordering their widest sections up to the 9th segment. Hind tibiae black from inner side, legs otherwise dirty yellow. Thorax with yellow spots from below. Sheath of ovipositor not enlarging apicad. Larval length reaches 10-15 mm; larva yellowish white with hazel head. S-shaped body without legs, curved, covered with sparse, short hairs. Anal segment is prolate, forming short, chitinized tube.
DistributionEuropean part of the former USSR to Latvia, southern Leningrad and Yaroslavl Regions; Crimea, the Caucasus, Transcaucasia, Western Siberia, Middle Asia; most common in forest-steppe and steppe zones. Widespread in Western Europe, Northern Africa, the Middle East (north Iran, Iraq, Syria), Hindustan, and southeastern Asia. Introduced into Canada and the USA.
ReproductionFemale lays 35-50 eggs, depositing them one by one in cereal stems, more frequently in upper internodes. Development of egg lasts 6 to 8 days; larval development lasts 20 to 40 days, depending on weather/climatic conditions in the area. Larva develops inside stem infested by egg. Developing larvae crawl down into lower part of stem, gnawing through internodes of culm. Larvae usually complete their development before the grain begins to ripen. During this period, damaged stem is easily distinguished by blacked-out area on culm below internode. The fully developed larva overwinters as pronymph. Pupation occurs in spring (from April until the first half of June); pupal stage lasts 7 to 10 days.
FoodOne of the most economically important insect pests of winter and spring soft wheat; also causes damage to hard wheat, rye, and winter and spring barley. To a lesser degree, it damages oats and millet. It also damages various sown and wild grasses, including brome, couch-grass (false wheat), timothy, and wild oat. Weight of grain decreases, and grain quality decreases because of damage to conducting vascular fibers by larvae. The under-sawed stems easily break off; as a result, losses of grain increase at harvest. Harmfulness of the Wheat Stem Sawfly varies widely, from 3 to 30%, depending on stem infestation. Control measures include stubbling and deep autumn plowing-in of stubble; harvesting as early as possible; two-phase harvesting of wheat with a close cut; use of resistant varieties with "filled" stems; and growing of less susceptible crops (oats, millet). Treatment by chemicals during the period of adult flight is ineffective; burning out of stubble does not substantially influence the larval death rate, but it does promote higher levels of entomophages mortality.
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