Nematus ribesii Scopoli Common gooseberry sawfly

This generally abundant sawfly is a notorious pest of gooseberry; infestations also occur on, for example, red currant and white currant, but not on black currant (cf. Nematus olfaciens, p. 252). Two- or three-year-old bushes are most likely to be attacked. Initial infestations tend to occur on the central, lower parts of bushes but they soon spread upwards and outwards. The larvae feed gregariously and rapidly defoliate the branches to leave only a skeletal framework of major veins. Heavy infestations cause considerable loss of plant vigour and cropping potential is reduced.

BIOLOGY

Adults occur from April or May onwards. Eggs are eventually laid in rows in slits made in the major veins on the underside of the leaves of host plants. The eggs hatch about 8-10 days later. Larvae then feed ravenously. They pass through

Fig. 336 Larva of common gooseberry sawfly. Nematus ribesii (x4).

several instars and become fully grown in about 3 weeks. Individuals then moult into active prepupae (these are sometimes thought to be larvae of a different species of sawfly; see description below). The prepupae soon disperse and enter the soil to spin oval, dark brown, parchment-like cocoons 10-15 cm below the surface. Individuals then pupate, and adults of the next generation appear shortly afterwards. There are usually up to three generations annually, and larvae occur throughout the summer into early autumn.

DESCRIPTION

Adult female 6-7 mm long, mainly yellow with a black-marked thorax; head black; antennae dark above and pale below. Adult male 5-6 mm long, dark-bodied; antennae entirely dark. Egg 1.2mm long, pale greenish-white. Larva up to 20 mm long; body mainly green, with the first, part of the second and last two body segments orange; pinacula large, black and shiny, each bearing one or more black setae; head black and shiny; thoracic legs black; abdominal prolegs seven pairs present (Fig. 336) (cf. magpie moth, Abraxas grossulariata, p. 228). Prepupa mainly pale bluish-green, with the first and last two body segments pale orange; pinacula inconspicuous.

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