Phyllotreta cruciferae Goeze A turnip flea beetle

This flea beetle is a generally common pest of Brassicaceae, including cabbage, cauliflower, kale, radish, turnip and watercress, and ornamentals such as nasturtium, stock and wallflower. Adults make small punctures in the cotyledons and leaves. These pit-like blemishes often coalesce, and damaged areas frequently develop into holes as the plants grow. Attacks are usually most serious in April and May, especially on seedlings or recent transplants whose growth is retarded by cold conditions or lack of moisture. Larvae burrow into the roots of host plants. They destroy the outer tissue and often cause extensive damage to the base of radish plants.

BIOLOGY

Adults are active from early spring onwards, when they feed on the leaves and cotyledons of cabbage, radish and turnip, and certain other members of the Brassicaceae. Eggs are deposited in the soil, close to host plants, usually in batches of 20-30; they hatch about 2 weeks later. The larvae attack the roots and feed externally for about 2 weeks. Individuals then pupate and new adults emerge another 2 weeks later, usually in late June, July or August. There is just one generation each year.

(b)

Fig. 220 Antennae of adult flea beetles: (a) genus Phyllotreta; (b) genus Psylliodes.

Fig. 220 Antennae of adult flea beetles: (a) genus Phyllotreta; (b) genus Psylliodes.

DESCRIPTION

Adult 1.8-2.4mm long, metallic greenish-black, somewhat rounded in outline; antennae 11-segmented (Fig. 220a) (cf. cabbage stem flea beetle, Psylliodes chrysocephala, p. 149), mainly black, with the second and third segments red or reddish; legs black. Egg 0.3 mm long, oval, yellowish-white, with dark plates and pinacula on the thoracic and abdominal segments. Larva up to 6 mm long; body white and slender; head black; thoracic legs very short.

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