Sitodiplosis mosellana Gehin Orange wheat blossom midge

This widespread and sporadically important pest occurs on barley, rye and wheat; second and subsequent winter wheat crops growing in sheltered sites are particularly liable to be attacked. The larvae feed deeply within the florets and 'attack' the developing grain (seed) producing tissue-dissolving enzymes. The larvae usually occur singly or in small numbers (cf. yellow wheat blossom midge, Contarinia tritici, p. 169). Affected grains are misshapen and discoloured; also, they do not enlarge fully and the loosened seed coat often splits. If three or more larvae are associated with a single grain, the inner tissue will be destroyed completely. Although heavy infestations cause yield reductions, the pest is of greatest significance for its overall effect on grain quality, especially as damaged grains may be invaded by secondary fungal pathogens.

BIOLOGY

Adult midges appear in June. After mating at emergence sites, the females migrate to new host crops to lay eggs. They rest by day, at the base of the crop, and are active mainly at dusk, especially in warm, calm conditions. The eggs are deposited in the florets, singly or in small batches; typically, the females select ears which are fully emerged from the enclosing flag-leaf sheath (Growth Stages 55 onwards) (cf. yellow wheat blossom midge, Contarinia tritici, p. 169). The eggs hatch within a few days at normal summer temperatures. Surviving larvae, often just one from each egg batch as mortality of eggs is often high, then feed for up to a month. Final-instar larvae retain the skin of the penultimate stage and such larvae, which appear superficially pupa-like, often remain within the ear up to harvest time, especially under dry conditions. Fully grown larvae (which, unlike those of C. tritici, do not jump) enter the soil, where they form cocoons and eventually overwinter. There is just one generation annually. Diapausing larvae are known to survive in the soil for many years before pupating and producing adults.

DESCRIPTION

Adult 1.5-2.5 mm long, reddish-orange to brick-red and relatively stout-bodied. Egg minute, reddish to orange-yellow, sausage-shaped. Larva up to 2.5 mm long, reddish to orange-yellow, tapering both anteriorly and posteriorly;

sternal spatula with an angular, distinctly bifid tip (Fig. 246d).

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