Family Pieridae

Pieris brassicae (L.) Large white butterfly

This species is an often common pest of vegetable brassicas, including broccoli, Brussels sprout, cabbage and cauliflower, but of significance mainly in allotments and gardens. Young larvae graze away the lower epidermis of the leaves but older ones cause extensive defoliation, and often reduce plants to a skeleton of stems and major veins. Plants are also soiled by accumulations of frass. Although capable of infesting field crops, including mustard, rape, swede and turnip, infestations on such crops are of little importance.

BIOLOGY

Adults of the spring generation occur in April and May. Eggs are then laid in batches, mainly on the underside of leaves. They hatch 1-2 weeks later, depending on temperature. The larvae feed gregariously and are fully grown in 4-6 weeks. They then pupate, usually suspending themselves by a strand of silk to a nearby wall, fence or other suitable support. Adults emerge 10-15 days later. Larvae of the summer generation occur from July onwards. In summer, large numbers of adults may arrive from abroad and these immigrants often boost resident populations. The winter is passed in the pupal stage.

DESCRIPTION

Adult 55-65 mm wingspan; forewings of male mainly white with the tip bordered in black (tip pale yellow below); forewings of female more extensively blackened above, including two subcentral black spots; hindwings mainly white above, yellow below. Egg 1.5 mm long, yellow, spindle-shaped and ribbed longitudinally. Larva up to 40 mm long; body mainly yellow to pale bluish-green, irregularly patterned with black; head black anteriorly, blue posteriorly (Plate 14b). Pupa 20-24mm long, dull greenish-grey to whitish, spotted with black.

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