Croesus septentrionalis L Hazel sawfly

This generally common sawfly attacks a wide range of deciduous trees and shrubs (including Alnus, Betula and Corylus). The larvae often cause extensive damage to young ornamentals and can rapidly defoliate the branches; they are also minor pests in cob nut, filbert and hazel plantations.

Fig. 332 Adult hazel sawfly, Croesus septentrionalis (x4).

over the head (a posture common to many species of sawfly larvae). Fully fed larvae enter the soil where they spin brown cocoons. In favourable districts, where there is a second generation of adults in August, larvae may be found from mid-June to early autumn. Second-generation larvae overwinter in their subterranean cocoons and pupate in the spring.


Adult 8-10 mm long; head, antennae and thorax black; abdomen mainly reddish-brown; legs black, the hind basitarsus and apex of hind tibia greatly expanded (Fig. 332). Larva up to 22 mm long; body pale yellowish-green to bluish-green, and partly suffused with yellow on the first thoracic and apical abdominal segments; prominent, black, rounded patches along either side of the body; head shiny black; abdominal prolegs seven pairs present (Fig. 333).


Adults appear in May and June. Eggs are then deposited in small slits made in major leaf veins of host plants. After egg hatch, the larvae feed gregariously and voraciously. They rest in groups, with each larva grasping the leaf edge with the thoracic legs and arching the abdomen

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