Ever since the use of insecticides was reduced in favour of biological control, British gardeners are discovering that some pests are on the increase (Financial Times, Oct 31/Nov 1, 1992). Now, there are friendly insects to control white flies, greenhouse red spider mites and vine weevils.
Encarsia formosa, a tiny wasp, lays eggs on white fly scales, and its larvae devour the scales, preventing more adult white flies appearing from them. To control the greenhouse red spider mites, the Pytoseiulus persimilis -- another mite -- can be introduced. Being meat eaters, the adults and nymph of the mite consume the adult and nymph of the greenhouse red spider mite. A minute nematode, often called eelworm, feeds on the grubs of the vine weevil, which eats leaves and damages plant roots.