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Large Cabbage White Butterfly

Scientific name: Pieris brassicae

Treatments

Caterpillar and eggs of Large Cabbage White Butterfly

The Large Cabbage White Butterfly is less widely distributed in the world than the Small. The caterpillars will be found on cruciferous crops, eg. cabbage, swede, kale, throughout the summer. The adult, nearly all-white butterfly emerges from the pupa (chrysalis) in April and May. The adult male has black markings on the tips of its wings; the female has the same marks with the addition of two black spots in the middle of each forewing. After mating the female lays 20 to 100 yellow eggs on the underside of cruciferous plant leaves.

After about 14 days the larvae (caterpillars) emerge then moult as they grow. They have well developed mandibles which they use with devastating effect on crops. This first generation pupates in June in a crevice or woody stem, emerging in July as the second generation which usually causes greater damage to crops in the garden, repeats the cycle and pupates to overwinter for the next year.

  
The Large White caterpillars are usually found in groups.

Apart from brassica crops they will use wallflowers and other cruciferous plants (four-petalled flowers), as alternate hosts. If the damage is extensive and the leaves look torn, the culprits may be Pigeons. Slugs leave a similar pattern of damage to the caterpillars and may have left the scene, but there will be a slime trail.
The caterpillar of the Box Tree Moth, which is stripping the leaves of Box plants in gardens throughout the British Isles, has similar colours and markings, but is a completely different species (Cydalima perspectalis). They also cover the plant with webbing.

Treatments Inspect the leaves of cabbage and turnips in July when adults are seen, for eggs and small caterpillars - crush by rubbing with a finger. They are usually around the outer edges where the female probably has a better grip while she places them in clumps. Covering the target plants with horticultural fleece or fine netting should prevent the butterflies laying their eggs in the first place. Netting should be held away from the leaves and not draped over them otherwise the butterfly may reach them. This has the additional benefit of protecting from Pigeons which will also feed on brassicas. Apantales glomeratus, a small wasp, is a biological control which lays its eggs in the caterpillar. These develop inside devouring the caterpillar - more suited to commercial growing. Another such control is a virus which attacks the caterpillars, turning them grey and causing death. Starlings and other small birds are predators, but if the crop has been netted they cannot reach them, so ensure the plants are clear of eggs and caterpillars before covering. Don't plant colourful, nectar bearing plants near to the vegetable plot as they attract the adults. Some people have reported that white, butterfly-sized objects, such as egg-shells, placed among the crop act as deterrents. The caterpillars can be sprayed with derris plus a wetting agent to keep the droplets on the waxy brassica leaves.

See also the monograph on the Small White Butterfly

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