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Biological Control of the Cabbage Whitefly

Aleyrodes proletella - in the public domain

Aleyrodes proletella - in the public domain

How to control the cabbage whitefly in an environmentally friendly way

The cabbage whitefly, Aleyrodes proletella (Order: Hemiptera; Family: Aleyrodidae) is one of many pests on Brassicacea (cabbage, sprouts, etc.).

It is a tiny insect (not longer than 2 mm), and with its four white-powdered wings it looks somewhat like a miniature moth. A great number of whitefly species exists, which all look very similar, and all belong to the same family. They occur on many different species of wild and cultivated plants. The cabbage whitefly, however, lives only on cabbage and other Brassicacea.

Biology of the cabbage whitefly

Adult whiteflies and eggs.

Adult whiteflies and eggs.

Eggs are laid at the underside of leaves, in circles, or semi-circles. Newly-born larvae are mobile for up to three days. Then their antennae and legs degenerate, and the larvae become immobile scales, which are tightly attached to the leaf. They feed on plant sap, until entering the non-feeding pupal stage, before finally emerging as adult whiteflies. This cycle continues throughout spring and summer, and three or four generations may occur each year. In autumn, when day length decreases, the adult females prepare for overwintering, by increasing the size of their fat bodies, and by halting the growth and development of their gonads. Males do not overwinter. After inseminating the females, they will eventually die during the winter.

Damage by the cabbage whitefly

Like aphids, feeding whiteflies excrete honeydew, which makes the leaves sticky and prone to become infested by black, sooty mould. Although cabbage whitefly are not a serious pest, the sooty moulds that they may cause, can weaken the plants indirectly, by cutting off light from the leaves. This may cause the leaves to fall prematurely, thus weakening the plant.

A gall midge.

A gall midge.

Natural enemies of the cabbage whitefly

An important enemy of the whitefly is a tiny, black wasp with a characteristic white abdomen: Encarsia formosa (Order:Hymenoptera; Superfamily:Calcidoidea; Family: Aphelinidae). This wasp is often used in greenhouses against the damaging greenhouse whitefly, Trialeurodes vaporariorum.

Other wasps of the same family parasitise cabbage whiteflies. These are completely black.

Female aphelinid wasps lay one egg inside each whitefly scale. When the larva hatches, it feeds on the whitefly larva, eventually killing it. Adult wasps emerge by cutting a hole in the top of the scale, and will soon be ready to parasitise other scales.

Another enemy is a species of gall midge (Order: Diptera; Family: Cecidomyiidae). The adult gall midges are very small flies with long legs, and their antennae are ringed with short hairs. The orange-red larvae are predatory and attack eggs and scales by piercing them and sucking out the fluids. The larvae overwinter in the soil, and in spring they pupate before emerging as adult flies.

Orius insidiosus attacking whitefly scales.

Orius insidiosus attacking whitefly scales.

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The ladybird, Delphastus pussilus is also a good biological control agent against whitefly. Its larvae feeds on eggs and nymphs and can consume up to 1000 whitefly eggs in its lifetime.

Other effective predators are the green lacewing, Chrysoperla carnea and the pirate bug, or flower bug (Anthacoridae) Orius spp.

The predatory mite, (Euselus spp), is often used against mites and thrips in citrus, but is also effective against whitefly scales.

Songbirds that feed on whitefly include phoebes, swallows and kinglets.

Sites on biological control of the whitefly - The use of various beneficials

Treatment of the cabbage whitefly

  • Hang yellow sticky traps above the plants. Tapping the plants will make the whiteflies to fly up. As they are attracted to yellow, they will fly straight into the trap. Take care not to wear yellow clothing, therefore, as you may carry the whitefly from plant to plant.
  • Hand pick older leaves, on which most of the whitefly will sit, and destroy these.
  • To prevent sooty mould from developing on whitefly-infested leaves, spray the underside of the leaves with water or diluted washing-up liquid. This will remove the honeydew on which the moulds grow.
  • Some plants will deter whitefly. These are, among others: rosemary, mint, hyssop, sage, marigold, but also onions and garlic. Plant these around your cabbages to prevent the whiteflies from settling.

Comments? Questions? Leave them here.

getmoreinfo on September 07, 2012:

Wow I learned something new, I love reading about the various insects.

Rosaquid on September 07, 2012:

Thanks for the environmentally friendly tips.

DuaneJ on May 30, 2012:

Very resourceful lens!

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