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"Imported" mites feed on mite pests in apples, grapes

photo of apple blossom
An apple blossom is tied to a grapevine for transfer of beneficial mites. Photo: A. Wise.

Spider mites, especially European red mites (ERM) are pests of both apples and grapes in New York. Previous IPM projects carried out in upstate New York orchards and vineyards have shown that ERM can be managed by enhancing existing populations of beneficial mites that feed on spider mites. One beneficial species, Typhlodromus pyri (T. pyri), can totally supplant the use of miticides in these locations.

Not all locations in our state are equally fortunate when it comes to mites. While both T. pyri and another beneficial species, Amblyseius fallacis (A. fallacis), occur naturally in western New York, only A. fallacis is commonly found in the other important apple or grape-growing areas of the state, the Hudson and Champlain Valleys, and Long Island. Both species feed on ERM, but T. pyri is a much more effective natural enemy for the following reasons: 1) T. pyri remains in the tree or vine all year, so it is always available to feed on spider mites; 2) T. pyri feeds on a wider variety of foods than A. fallacis does and can therefore remain at high densities even when populations of ERM are temporarily low; 3) T. pyri can detect the presence of ERM via chemical cues and prefers to feed on it; and 4) T. pyri survives northeast winters better than does A. fallacis.

In 1996 Cornell scientists transported T. pyri from western New York into the Hudson and Champlain Valleys and elsewhere in the northeast. How does one move microscopic creatures from one orchard to another? Researchers have observed that when apple trees are in bloom, beneficial mites congregate in and near the flowers to feed on pollen. In May of 1996, apple blossom clusters were collected from an orchard at the Experiment Station in Geneva and were sent to 9 orchards in New York and 32 orchards in 6 other northeastern states. The clusters were then attached to apple trees in the recipient orchards, and the T. pyri made those trees their new homes.

Mites were again released in July, when apple leaves from Geneva were stapled to leaves in the 41 recipient orchards. Leaf samples from each site were later collected and sent back to Geneva. They were put through a mite brushing machine, and the beneficial mites that fell off the leaves were counted under a microscope. T. pyri were found in samples from all but 3 of the 41 sites. Now that they have become acclimated to these new regions, researchers expect that T. pyri will provide biological control of European red mite during the 1997 growing season.

In the vineyard study, T. pyri collected from an apple orchard in Geneva were successfully established in two Long Island vineyards. The effect of fungicides on T. pyri was measured in these vineyards. Mite densities following treatments showed that one commonly used fungicide is very toxic to T. pyri. The next step in biological control of spider mites is to find an alternative to this fungicide for management of grape diseases.