This sawfly is a minor pest of grasses and cereals, including wheat and barley. The larvae graze openly on the leaves and typically devour the tissue from the tip downwards. Affected leaves often appear severed and frequently attract
Fig. 333 Larva of hazel sawfly, Croesus septentrionalis (x4).
attention; damage, however, is of little or no importance.
Adults occur mainly from May to June. Eggs are deposited in the edges of expanded leaves; each egg enlarges before hatching to produce a prominent swelling in the leaf lamina. Larvae are most numerous in June and July. They feed on the leaf tissue for 4-6 weeks before becoming fully fed. They then moult into active prepupae and enter the soil, where they eventually pupate but without forming cocoons (cf. Pachynematus clitellatus, p. 252). There is one generation each year.
Adult 9-10 mm long, mainly metallic black with a green and bluish sheen; pronotum and tegulae red (in female). Larva up to 18 mm long; body greenish-white to creamish-white, but blackish dorsally, with a black mark over each thoracic leg; head marked with black; abdominal prolegs eight pairs present (Plate 16d).
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