Aleyrodes proletella L Cabbage whitefly

Cabbage whitefly is a widespread and locally abundant pest, especially in southern areas. Infestations occur mainly on cultivated brassicas, including Brussels sprout, cabbage (especially savoy cabbage) and cauliflower, but are usually of only minor importance. The underside of infested leaves becomes marked by patches of white, mealy wax (Plate If); plants are also contaminated by honeydew and sooty moulds, a par ticular problem on Brussels sprout. Under dry conditions, heavy infestations reduce the vigour of young plants and may cause plants to wilt. Infestations are often first noticed when, on disturbing the plants during the spring, summer or autumn, clouds of adults rise into the air; the adults may even become active, and attract attention, on sunny yet frosty days in mid-winter.

BIOLOGY

Breeding commences in the spring, and females then deposit small semicircular groups of eggs on the underside of leaves of host plants. The eggs hatch in 1-2 weeks. At first, the young nymphs wander over the leaf surface but they soon settle down to feed. Individuals are fully grown in about 10 days. They then pupate and adults appear a few days later. There are four or more overlapping generations annually, with adults and some pseudo-pupae overwintering.

DESCRIPTION

Adult 1.4-1.6 mm long, mainly yellow, coated with white, mealy wax; head and thorax marked with brown; forewings white, each with two grey spots. Egg 0.25 mm long, whitish, oval. Nymph flat, scale-like; mainly white, with a pair of yellow spots; eyes red. Pseudo-pupae pale yellow, flat and scale-like, with a waxen fringe; eyes red.

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