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Putting the Bite on Plum Curculio WeevilsBy Linda McGraw
June 6, 2001
Anyone who has ever bitten into a "wormy" apple will appreciate the efforts of Agricultural Research Service chemist Fred J. Eller, who has developed and patented a pheromone bait that can give fruit growers an early warning of plum curculio weevils. Pheromones are chemicals secreted by animals, especially insects, that influence the behavior or development of others of the same species, often acting as a sex attractant.
Plum curculio weevils, Conotrachelus nenuphar, attack apples, peaches, cherries, pears, apricots and plums in the southern and eastern United States. Adult female weevils lay eggs under the skin of developing fruits, causing yield loss and scarring. Normally, growers become aware of the pests only after the eggs are laid, when a telltale "crescent moon" blemish appears on the fruit. Once this moon appears, the fruit is permanently scarred. The plum curculio is only one-quarter inch long, with a brown and gray body, and a long snout. The female beetle lays her eggs inside pome and stone fruit, causing "wormy" fruit.
Eller, based at ARS National Center for Agricultural Utilization Research at Peoria, Ill., identified the pheromone released by the male curculio weevil. The chemical attracts both female and male curculios. He incorporated the chemical, called grandisoic acid, into a trap that was originally designed for boll weevils by ARS researchers in Mississippi. Eller placed several traps baited with the chemical attractant in orchards at blossom time. He found significantly more weevils in the baited traps than in the unbaited traps.
More work is needed to expand the use of the pheromone and to add volatile compounds, such as fruit odors, to enhance the attractiveness of the pheromone and capture weevils even at low densities. Currently, other researchers at the ARS Appalachian Fruit Research Station, Kearneysville, W.Va., are combining the pheromone that Eller identified with apple odors to make a more attractive lure for the plum curculio.
Ultimately, a pheromone-baited trap may one day offer a reliable monitoring tool to help growers reduce pesticide use by spraying only after pest populations are detected and prior to significant crop damage. ARS is seeking companies to license the technology.
ARS is the chief scientific research agency of the U.S. Department of Agriculture.