Researchers have been unable to duplicate whatever it is in apples that attracts codling moths.

Dr. Peter Landolt, research leader at the U.S. Department of Agriculture’s research lab near Wapato, Washington, had been hoping to pinpoint what attracts the moths to the fruit and use an artificial version as a lure for monitoring the pest or as part of a control strategy. The advantage of using kairomones (volatiles extracted from the host plant) rather than insect sex pheromones is that they are attractive to both male and female moths.

Drs. Doug Light, with the USDA in Albany, California, and Alan Knight at the Yakima lab, have done that with a volatile originally derived from Bartlett pears, but Landolt said that in three years of testing he’s not found anything in apples that is strong enough to work.

Codling moths find apples in part by chemical odor, he said. When infested apples or ripe apples, which are giving off a ripe apple aroma, are placed in an orchard where the fruit is still green, they attract codling moths.

Theoretically, if the moths are attracted to apples by odors, scientists should be able to reproduce that and use it as a lure.

“We know there are several apple odor chemicals that are attractive to codling moth,” he reported to the Washington Tree Fruit Research Commission, which funded the project. “But where we identified the compounds and tested the synthetic compounds in the field, they are weak compared to the pear ester. I’m assuming that makes them impractical for any monitoring or control. I’m still thinking we don’t know how moths are selecting and finding apples.”

Landolt’s tests showed that beta farnesene, E,E-alpha farnesene, and ethyl caproate with ethyl benzoate were mildly attractive to codling moths in the field. Although male moths responded significantly to a blend of nonanal, bergamotene, ethyl caproate, methyl benzoate, and methylbutyl acetate, the attraction was weak compared to that of pear ester or pheromone. The response of females to alpha farnesene or beta farnesene was inconsistent. Ocimene and linalool appeared to repel the moths.

Landolt said he’s not sure if there was a problem with the release rates used in the tests or the ratio of the compounds in the blends tested. There might also be a problem with the type of trap used in the experiment.

Competition from foliage and fruit odors and from other tested lures could be an additional factor, he said.