Apion vorax Herbst Bean flower weevil

This weevil is a minor and usually sporadic pest of field bean. The adults form small, rounded

Fig. 225 Clover seed weevil, Apion trifolii (x25).

holes (c. 1mm in diameter) or elongated punctures (c. 3 mm long) in the leaves but are of significance only as vectors of viruses such as broad bean stain virus (BBSV) and broad bean true mosaic virus (BBTMV); these viruses are also transmitted, but to a lesser extent, by pea & bean weevil, Sitona lineatus (p. 161). Damage to bean flowers by larvae is of no significance.

BIOLOGY

Adults overwinter in woodlands and become active in the early spring. They occur and often feed on plants such as Galeobdolon luteum, Mercurialis perennis, Rubus fruticosus and Urtica, before migrating to field bean (and other members of the family Fabaceae) upon which they are able to breed. Adults may be found in bean fields from late April or early May onwards, where they feed on the leaves and where eggs are eventually laid in the flowers and flower buds. The eggs hatch a few days later. Larvae feed on the pistils and styles for about 2 weeks before eventually pupating, usually amongst the shrivelled remains of the keel petal. Adults emerge shortly afterwards. Development from egg to adult takes about a month and there are up to two generations annually.

DESCRIPTION

Adult 2.5-3.5 mm long, mainly black; elytra bluish-black, with a metallic sheen. Egg 0.45 mm long, oval, yellowish. Larva up to 4 mm long; body translucent to creamish-white; head black. Pupa 3.0-3.5 mm long, whitish, translucent.

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