Bruchus rufimanus Bohemian Bean beetle

This generally common beetle is usually a minor pest of broad bean and field bean; it will also, occasionally, attack pea. In spring, the adults feed on the pollen and petals of the flowers but damage caused is of no significance. The larvae feed on seeds inside the developing pods. Characteristically, they bore within the cotyledons of the young seeds without destroying the germ; germination of damaged beans kept for seed, therefore, is often unimpaired. A previously infested bean (seed) may be recognized by the presence of a relatively large hole, c. 2 mm in diameter, through which the new adult beetle has emerged. One consequence of such damage in stored beans is contamination, owing to the frequent lodging of wild oat seeds in these emergence holes. Infestations of this pest are encouraged by hot, dry summers. Although infested beans may be taken into store, this insect is not a storage pest, as the larvae are unable to invade, or to survive in, dried beans.

BIOLOGY

Adults hibernate amongst leaf litter and in various other sheltered situations, emerging in the late spring. Eggs are laid singly on the outside of the developing pods of beans during April or May. The eggs hatch in up to 1-3 weeks, depending on temperature. The larvae immediately bore through the pod wall and attack the developing seeds. Each larva bores within the seed and becomes fully grown 2-3 months later. There are four larval instars. Pupation occurs within the attacked seed, the larva firstly boring to the bean surface and making a rounded hole covered only by the opaque outer seed coat. The adult stage is attained about 2 weeks later, but individuals usually remain within the pupal chamber for an extended period and may not emerge until after the crop has been harvested and placed in store; some adults may remain within infested beans until the following spring. Young adults are often common in the vicinity of bean crops during the later summer and autumn, before they enter hibernation. There is just one generation annually.

DESCRIPTION

Adult 3-5 mm long, mainly black, clothed with greyish to creamish-white hairs; elytra black, marked with irregular patches of pale hairs, and noticeably shorter than the abdomen; antennae with the basal four segments reddish; legs relatively long, with the anterior femora, tibiae and

Fig. 211 Hindleg of bean beetle, Bruchus rufimanus.

tarsi reddish; hind tibiae with a distinctive apical spine (Fig. 211). Egg 0.5 x 0.25mm, oval and flattened, yellowish-green. Larva up to 6 mm long; body creamish-white; head brown, with powerful mandibles; thoracic legs present but minute.

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