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The Pamphlet Collection of Sir Robert Stout: Volume 14

The Pea And Bean Beetles. Bruchus pisi. Linn. Bruchus granarius. Linn

The Pea And Bean Beetles. Bruchus pisi. Linn. Bruchus granarius. Linn.

Fig. XVII.

Fig. XVII.

1, Bruchus granarius, nat. size; 2, mag.; 9, Bruchus pisi, nat. size; 10, mag.; 4 and 5, larvæ;, nat. size, and mag; 6 and 7, pupa, nat. size and mag.; 11, pea with Bruchus pisi escaping; 3 and 8, beans attacked by Bruchus granarius.

In very many samples of peas and beans of all kinds there are some of the pulse which have tiny holes in them, with dark edges. If these pulse are split open with a knife it will be seen that the insides are more or less eaten away, scooped out as it were. In some cases, although there may be no holes in them, the pulse look unhealthy and not of a proper colour.

Upon opening these a maggot will be found which is evidently feeding upon the contents of the pulse. The best sorts of peas for podding grown by market gardeners, and for seeds-men by farmers, are frequently much injured in this way, and it has been noticed that the large and broad bean known as the Mazagan is often seriously affected. Winter beans are more page 58 liable to be attacked than those spring sown. Foreign peas and beans are worse as a rule than those grown in this country.

Though the embryos of the pulse are most generally left intact by the larvæ or maggots within them, the vitality of the seeds must be greatly impaired, and the plants from them, if indeed they are able to produce these, will be weakly, inasmuch as the supply of starch stored within the cotyledons for the support of the embryo and the young plant is diminished, and the other essential functions of the cotyledon are materially impaired.

Samples of peas and beans have been observed in which from twenty-five to thirty per cent, of the pulse had holes in them, showing their former occupation by the larvae of these beetles. Obviously there would be a serious loss of plants if these seeds were sown, and a serious diminution in food value if they were consumed by animals. These insects are very destructive in America and Canada, so that in some parts of the latter country peas and beans cannot be cultivated. Harris states that the Pea beetle is supposed to be a native of the United States, and that it may have been introduced from there into England.*