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Releasing beneficial wasps in New York orchards

An insect called the oblique-banded leafroller (OBLR) is a very costly pest of apples in New York. Its immature life stages feed on apple blossoms and on developing fruit. Many OBLR-damaged apples drop from the trees prematurely; a small percentage remain on the trees, but these develop deep, corky scars and indentations.

Growers with orchards heavily infested with OBLR can experience 5 to 10 percent fruit injury, even when they have applied multiple sprays of the most effective insecticides available. In 1996 New York apple growers as a group lost $2.7 million in revenues because of fruit sales thwarted by OBLR damage. Finding an effective means of managing OBLR, which has developed resistance to many chemical treatments, will be a tremendous coup for the New York apple industry.

Last summer Harvey Reissig and Jan Nyrop, Cornell entomologists, investigated the potential for biological control of OBLR by a wasp called Trichogramma platneri, which feeds on leafroller egg masses but is harmless to people and livestock. The wasps were released in large numbers in both a commercial orchard and an unsprayed, research orchard. Rates of parasitism of OBLR egg masses by the wasps were recorded for several weeks.

The wasps' effect on OBLR damage varied. Leafroller damage to McIntosh and Cortland apples at the research orchard was 50 to 70 percent lower than in plots where no wasps were released. But damage in the Delicious apples in the same orchard was not at all reduced by T. platneri. In the commercial orchard, damage was reduced by 10 percent in Jerseymacs, but the wasps seem to have had no effect in the Cortland plots.

The wasps alone are not likely to provide adequate management in orchards heavily infested by OBLR. But using beneficial wasps in combination with other control methods could well enable New York apple growers to reduce insecticide applications for leafrollers by 30 to 50 percent. Replacing standard insecticides with the wasps may also enhance the development of biological control of mites.