Biological control of glasshouse red spider mite

Glasshouse red spider mite is difficult to control as it breeds rapidly in warm conditions and some mite strains have developed resistance to some insecticides. Biological control is an attractive alternative as it avoids these resistance problems, as well as the risk of spray damage to plants.

There are several biological control predators available for treating glasshouse red spider mite infestations. Phytoseiulus persimilis, a tiny, orange mite, is the most commonly used biological control of glasshouse red spider mite. Adult and nymph Phytoseiulus persimilis are best released on outdoor plants in summer. More active than glasshouse red spider mite, these predators feed on all spider mite life stages. Amblyseius mites are less efficient than Phytoseiulus mites but are useful as a preventative control, particularly in winter. The larvae of Feltiella acarisuga, a predatory midge and British native, can be introduced in spring if it is suspected that red spider mite have overwintered on plants.

These predators are susceptible to insecticides, so biological control cannot be used the same time as chemical controls. The only exceptions are those insecticides with very short persistence, such as vegetable oils or fatty acids, which can be used to keep mite numbers down before it is time to introduce predators.