Although sex is a strong attractant, food can sometimes be a bigger draw. Such is the case with a chemical that scientists have discovered in pears that has just the right scent to attract codling moths to traps. This discovery is part of a larger University of California program to control codling moth pests in homeowners' backyard trees.
The novel chemical is pear ester, which serves as the natural taste of Bartlett pears used in pear-flavored jellybeans. Moths have apparently evolved to detect this odor and use it to locate a preferred food, like ripening pears.
Placed in traps that are hung in trees, sex attractants called pheromones have been the main tool for growers for monitoring codling moths in orchards. Pheromones are chemicals that female moths give off to attract males for mating. Unlike pheromones that only attract male moths, the pear ester attracts both sexes.
Entomologist Douglas Light, USDA-Agricultural Research Service, discovered the chemical. Light and fellow entomologist Alan Knight worked together to field test it in apple, pear and walnut orchards.
"We discovered that pear ester acts as a kairomone," Knight said. "Unlike pheromones, which involve only one species, kairomones are chemicals emitted by one species -- in this case pears -- that attract and benefit another species, such as codling moths. We hope that by using pear ester, we can capture enough females to provide control."
Codling moth, the infamous "worm" in the apple, is tough to manage in the home orchard. Soon after hatching, caterpillars bore into apples, pears, or walnuts and feed, leaving reddish-brown droppings, or frass.
Codling moth adults are about one-half to three-quarters of an inch long with mottled gray wings they hold tent-like over their bodies. Their appearance blends well with most tree bark, making them difficult to detect. If trapping the adults, codling moths can be distinguished from other moths by the dark, coppery brown band at the tip of their wings.
Knight is working with UC Cooperative Extension farm advisor Dan Marcum of Shasta and Lassen counties and UC Integrated Pest Management advisor Carolyn Pickel of Sutter and Yuba counties to spread the word about the new discovery as part of their Selective Organic Fruit Tree (SOFT) program. The program is funded by the UCCE Integrated Pest Management Demonstration Grants Program.
The project has a multi-pronged approach controlling codling moth, including better cultural practices, like pruning; trapping females and males with new lures and traps; and releasing natural enemies, like the granulosis virus and insect-feeding nematodes.
Through the SOFT program, scientists hope to give homeowners an effective program using several certified-organic-approved methods to produce worm-free fruits and nuts in backyards. In turn, reduction of moths in backyard trees can reduce the potential for the pests to migrate into commercial orchards, a matter of growing concern with the encroachment of suburban developments into agricultural areas.
Knight, Marcum and Pickel are taking their project to residential areas starting in the small town of McArthur in Shasta County -- population 365.
McArthur is one square mile, and every home has one or more fruit trees, with 75 percent of the trees infested with codling moth. Coupled with the low population and absence of nearby commercial production, the area is an ideal test site. The town's Wayside Garden Club boasts 200 members who are keenly interested in backyard horticulture and may serve as a catalyst to successfully implement the SOFT program.
"First, we surveyed homeowners and asked why they grow the trees -- for fruit or shade? What do they do with the fruit -- eat it, or give it to livestock? Do they prune or spray?" Knight said.
This baseline information set the stage for Marcum to design six workshops on pruning trees. Marcum suggested hand thinning to remove all infested fruit during each generation before worms leave the fruit and also advised removing dropped fruit. Thinning out the infested fruit has the added benefit of encouraging the remaining fruit on the tree to grow larger.
"Our goal is to bring codling moth populations down to a low level so the area can have clean apples this fall," Marcum said. "The approach is an area-wide urban program to improve codling moth control and to reduce the use of pesticides."
Knight followed up with one workshop on codling moth. He told the group that they can make their own pheromone traps, preferably something fairly clear that they can see through to easily identify the codling moths in the trap from the ground. Just add 30 percent vinegar to the pear ester lure.
"Nearby backyard trees where no control program is in place can serve as a continual source of codling moths, thus making it even more difficult to limit damage. I encouraged the audience to get their neighbors involved in the process," Knight said.
The scientists also encouraged the backyard gardeners to spray on the granulosis virus, which is specific to codling moth and accepted by organic growers.
"The codling moth granulosis virus is a naturally occurring baculovirus that makes the worms lethargic and eventually dissolves them from the inside out," Marcum said. "Baculoviruses infect only arthropods, that is, insects and related species. While one of only a few available choices for organic farmers, the baculovirus should also be of interest to those who now use chemical pesticides and want to reduce dependence on them."
The third technique is to spray parasitic nematodes onto tree trunks to destroy populations of codling moth larvae that lie dormant during the winter. Parasitic nematodes are available in small quantities for residential use. Moderate temperatures and available moisture are key factors affecting the activity of nematodes, so sprays applied in the spring and fall can be very effective. Gardeners can easily use a garden hose to wet their backyard trees.
Scientists hope to extend this program across the state and into southern Oregon, if they can get more funding.
"We have high hopes that this cooperative neighborhood-centered program will empower homeowners to bond together to control a mobile pest impacting their community," Pickel said.