Breakthrough in codling moth control
A pear ester has potential for both monitoring and controlling the pest in apples and pears.
Dr. Doug Light with the U.S. Department of Agriculture’s Western Regional Research Center in Albany, California, and Dr. Alan Knight with the USDA’s Agricultural Research Service lab in Yakima, Washington, received a 2005 Technology Transfer Award from the USDA for “outstanding efforts in the development and transfer of environmentally friendly technologies that substantially enhance monitoring and control of the codling moth on apple, pear, and walnut crops worldwide.”
Here, the two researchers explain how a pear ester derived from Bartlett pears can be used in monitoring and controlling codling moths.
The discovery that codling moth is attracted to pear ester has opened up new possibilities for monitoring and controlling this important pest.
Dr. Doug Light, entomologist with the U.S. Department of Agriculture in Albany, California, describes it as a breakthrough that could revolutionize codling moth control. He discovered the ester’s attraction for codling moth about six years ago while testing a collection of plant volatiles held in a repository at the Albany research lab. Of all the compounds, the ester, which was derived from ripe Bartlett pear, was by far the most attractive.
The ester—a volatile called ethyl (E,Z)-2,4-decadienoate—attracts both male and female moths, not just the males as pheromone lures do, and is attractive to young codling moth larvae as well.
Working with Dr. Alan Knight, entomologist at USDA’s Yakima Agricultural Research Laboratory, Light developed lures containing synthetic pear ester for trapping and monitoring codling moth. The researchers think that the pear ester lures (known as DA lures) will eventually replace the pheromone traps that are still widely used today because the lures can directly measure the activity of female moths in the orchard, which can differ from male activity and behavior. With pheromone traps, male behavior is monitored in order to extrapolate information on activities of the females, such as egg laying.
“Instead of predicting female activity based on capture of male moths, you’re dealing with real biology,” Light said. “It’s more straightforward.”
With a picture of what’s actually happening, growers should be able to time controls better or avoid using unnecessary sprays, which translates to less impact on the environment and lower costs to growers, Light said.
The DA lure can be used in apple, pear, or walnut orchards, though it might be less effective in pears where there is fruit injury or towards the end of the season, when the pears start to give off natural ripening odors.
Researchers have found DA lures in apple work best in Granny Smith blocks, but Knight said it appears to be effective in Comice, Bosc, and d’Anjou pear orchards also.
Knight said the DA lure is not as strongly affected by the pheromone released from dispensers used for mating disruption as a pheromone lure and doesn’t pull moths in from a great distance, as pheromone traps might do.
“Our studies have measured population levels within a hectare (2.5 acres) around each trap and correlated injury with trap counts. Pear ester gives you a good measure of the local population.”
But Knight said growers would probably want to continue using pheromone traps along with pear ester traps at first because they know how to interpret their results. Also, a good pheromone trap enables the grower to monitor moth populations in and around the orchard. The pear ester trap, on the other hand, would be good for measuring moth activity in specific locations, such as near bin piles or on borders. One useful approach may be to alternate pear ester and pheromone traps in the orchard.
The absence of moths in a trap does not necessarily mean there are no moths in the orchard, Knight said, but if a pear ester trap catches moths, it’s an excellent indicator of a pest problem.
A combination lure containing pheromone and pear ester has proven to be very effective to monitor codling moth in mating-disrupted orchards. Knight said studies have shown that the pear ester greatly increases the attractiveness of the pheromone to the male moths.
Early in the season, the DA lure is almost equivalent to the pheromone lure in its attractiveness in apple orchards, but later in the season, catches in the pear ester trap can be lower. One strategy that the researchers have considered is to have growers use the DA lure to set female biofix for the first generation and then use pheromone or the combination lure to monitor moth populations later in the season.
Attract and kill
Knight and Light have also been testing the pear ester attractant as an attract-and-kill strategy. Mass trapping with 50 to 100 traps per acre using a combination DA-pheromone lure as a bait only reduced fruit injury by about 50 percent in trials. Knight has experimented with new types of killing stations and has developed a vertical grid made of bird netting that is treated with an insecticide and baited with the combination lure. He suggests that this technique could be used to augment mating disruption or other types of control in hot spots such as bin piles and borders, or in neighboring backyard trees. During 2005, using only 24 panels per acre, Knight and Light were able to reduce fruit injury by 75 percent in a pheromone-treated Granny Smith block in California.
The pear ester has also been tested as a microencapsulated spray formulation and in hand-applied “puzzle piece” dispensers for mating disruption, either alone or in combination with pheromone. In tests last summer, the ester-and-pheromone dispenser gave better disruption of mating than pheromone alone.
“In an orchard with mating disruption, we suppose that male moths follow the false trails of pheromone released by dispensers, ‘thinking’ it will lead to females,” Knight said.
After a time, it appears that males look for rendezvous sites where females are likely to be, and those are usually near fruit, so that larvae that hatch from the eggs they lay are near a source of food.
The researchers think that male moths zero in on the combined odor of female moths and ripe fruit thinking they are going to be especially lucky, but instead they are just really confused.
Towards the end of the moth flight, when the males are getting older, they seem to be more interested in the ester [food] than the pheromone [sex],” Knight observed.
The combination dispensers are in the experimental stage and might be available in two years.
The U.S. Environmental Protection Agency reviewed the use of pear ester for pest control purposes and declared it to be a benign natural product. It is used as a food flavoring and is an ingredient in confectionary, Knight said.
The pear ester is attractive to newly hatched codling moth larvae as well as to adult moths. Light and Knight have been looking at the idea of using pear ester as an adjuvant with a regular insecticide spray.
The tiny capsules of ester become point sources on the leaves that attract the larvae and encourage them to spend more time wandering on the leaf, where they are exposed to insecticides, rather than going straight to the fruit and burrowing inside, where they are protected.
Knight said adding the ester to low rates of Guthion (azinphos-methyl) reduced injury by as much as 60 percent in tests last summer in apple. The effective rate of ester was high—perhaps higher than would be economically feasible—but lower rates have been very effective in walnuts. This summer, Knight will investigate this rate issue in Granny Smith where the pear ester seems to be the most attractive. Knight calls this cultivar the “walnuts of apple.”
“We also want to look at this adjuvant effect with some of the newer classes of insecticides, like insect growth regulators and neonicotinyls, that probably need some additional help,” he said.
A lot of progress has been made in developing the pear ester as a new tool to manage codling moth since Light’s discovery. With so many potential applications of the ester to be explored, both Knight and Light are thrilled that a large number of scientists in California, Oregon, Washington, Michigan, and other fruit-producing regions around the world are working with it.