Even pests have pests, and often growers can encourage those natural enemies sufficiently to keep crop pest populations at tolerable levels. For example, the cottony cushion scale was once a big problem in the California citrus industry, but a natural predator called the videlia beetle greatly reduced the problem once it was introduced into the state.
The grape leafhopper can be a damaging pest, but when growers plant wild blackberry vines near their vineyards, they encourage the build-up of a certain kind of parasitic wasp which attacks the blackberry leafhopper species in addition to the grape leafhopper. This can keep the grape leafhopper numbers sufficiently low, reducing the need for pesticidal control. Some insect predators and some parasites of insects are raised commercially for release on farms. Growers can also control some diseases and nematodes by applying biocontrol agents such as bacteria, nematodes or fungi which act as hyperparasites.
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