Leaflets. Nos. 1 to 100 / Board of Agriculture and Fisheries.

  • Great Britain. Board of Agriculture and Fisheries.
Date:
1917
Catalogue details

Licence: Public Domain Mark

Credit: Leaflets. Nos. 1 to 100 / Board of Agriculture and Fisheries. Source: Wellcome Collection.

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    are so steadily and constantly beset by the insects, and their leaves are so much bitten, that they never make good roots. When the roots are formed, and are of some size, late generations of beetles pertinaciously stick to them, in some: seasons even until September. The turnip flea-beetles not only attack turnips and swedes, but are sometimes destruc- tive to rape, mustard, cabbage, kohl-rabi, and other cultivated cruciferous plants. Description and Life History of the Beetles. The Common Turnip Flea (P. nemorum) is very small,. being only about one tenth of an inch long. It is black, bluish-black, or greenish-black in colour, with a broad yellow stripe down each wing-case. The antenne are: 11-jointed, the three joints nearest the head being yellow, the others dark-coloured. The legs are ochreous, or yellow, and the thighs, which are very stout, are well adapted for: the long jumps which this insect’ can make. Like all fiea. beetles, it passes the winter in beetle form under clods and stones, in tufts of grass, among weeds, beneath the bark of trees, and under rubbish of various kinds, by the sides. of fields, hedgerows, and ditches. It is thus sheltered during the winter, and it is sustained throughout the early - spring-time, until the turnip seed has germinated, upon wild cruciferous plants, such as charlock, hedge-mustard, and wild radish. It has a wing expanse of more than a quarter’ of an inch (Figs.1 and 2), and takes long flights in search of congenial food, which it scents from a distance. In its. feeding it shows a preference for the seed leaves, and for the plant in its youngest stages, ¢.g., when the plant is most delicate and least able to withstand injury. The beetles lay their eggs on the under sides of the second or “rough” leaves. From these eggs, tiny yellow larve come in five. or six days (Figs. 8 and 9), which, mining (Fig. 7) in the leaves, and feeding upon the soft tissues, greatly weaken the plants. When full grown, the larve are rather mors than + of an inch long, with six front feet and “sucker foot” at the hind end. In the course of from five to seven days, they fall to the ground and change to pupe (Figs. 10: and 11), from which, in about 12 days, the perfect beetles. come and proceed to attack the turnip-plants. It is said thatas many as six generations may be produced in a season, if weather and other conditions are favourable. P. undulata, an allied species, is often also very trouble- some on the turnip crop ; itis slightly smaller than nemorwm, and has dark-coloured legs. P. cruciferae is another species that attacks cruciferous. crop plants.