Mating disruption keeps male and female codling moths from finding one another, preventing them from procreating and effectively reducing the codling moth population in the orchard. These pests of apples and pears emerge in early spring, after overwintering as full-grown larvae. Codling moth (Cydia pomonella) overwinters in leaf litter or under loose bark scales or other protected location in the orchard. As temperatures increase to about 50º F, the cocooned larvae mature into moths, with pupation occurring around first pink. First flight is roughly at full bloom, and full flight happens several weeks later.
After mating, eggs are deposited on or near fruit. After six – 10 days, these larvae emerge and bore into fruits, first feeding near the surface, and later feeding on seeds and inner flesh as they grow. Thirty days later, larvae emerge from the fruit and migrate to a sheltered spot to cocoon.
Codling moths can produce several generations each growing season. Some first generation larvae will pupate during the same growing season, while others remain cocooned until the next spring. Those that do pupate will mate in the canopy, and lay eggs that hatch the next generation of larvae. Some of this second generation larvae will also pupate, producing a third generation larvae in mid-summer.
Codling moth damage includes “stings,” or shallow scars where larvae only fed on the surface. If the larvae continue to feed and grow, their excrement or frass will flow out of the entry and exits holes in fruit. Fruit infected by the first generation of larvae in spring will drop.
Codling moths are active between 55º and 80º, and are more active in warm, dry springs than in cold, wet ones. Mating disruption helps to decrease codling moth populations while preserving the efficacy of insecticides. Degree day models can help time the placement of pheromone traps.
“Pheromone-based pest management is increasingly important,” Don Thomson of Pacific Biocontrols Corporation said during a Washington State University Tree Fruit Extension Virtual Winter Institute presentation on IPM in apples. “We have a lot of different insecticides, but a lot of them are older insecticides.”
With little new product development, mating disruption as a primary tool to combat codling moth is needed to “protect the efficacy of the products that we have,” he said.
Dispensers which release codlemone (the pheromone released by female codling moths) can either be reservoir dispensers or aerosol dispensers. The former release the hand-applied chemical in response to temperatures, while the latter – puffers and misters – are an active release system, which can be shut off and can be programmed depending on growing conditions and pest activity.
Passive systems are placed throughout the orchard at a recommended rate of up to 400/acre, distributed uniformly. The dispensers release a plume of chemical when temperatures are within the active range of the codling moth. The plume moves downwind, confusing nearby male codling moths, who aren’t sure where to find females, in a process known as competitive attraction.
The passive system depends upon the density and distribution of the dispensers. As the density of dispensers per acre increases, codling moth traps demonstrate a decrease in capture. If the number of dispensers per acre is decreased, greater amounts of codling moths are found in pheromone traps. But it is not a linear correlation, Thomson said, and twice the number of traps doesn’t double the reduction in captured moths.
The percentage reduction in moths also depends upon the initial pest pressure, as more codling moths in the orchard means less competitive advantage for the mating disruption system.
“Point sources are important, and so is population density,” he said. “You need low populations in order for codling moth mating disruption to work effectively. Codling moth mating disruption is density dependent.”
Research shows that passive dispensers evenly distributed disrupted 97% of codling moth mating activity on average, while the same number of dispensers placed in only a few sites dispersed across the orchard disrupted 87% of mating activity on average. Only 76% of mating activity was disrupted on average when all the dispensers were placed together in one location.
Because codling moths aren’t going to be dispersed evenly in the orchard, but rather found in “hot spots” where population density is higher, dispensers located in densely populated regions won’t be as effective.
Aerosol dispensers only require one or two units per acre, as a very large amount of chemical is released. These dispensers contain a propellant, which pushes the chemical out into the surroundings forcefully. Two aerosol units per acre will suppress 90% of the mating activity.
“The aerosol plume moves differently. They move quite differently than do the plumes coming off of hand-applied dispensers,” Thomson said.
But even with the huge and widespread release of pheromone from the aerosol dispenser, some males will still move around the edges of the plume and find females. The windward border around each dispenser is susceptible to increased mating success, resulting in localized increases in codling moth populations and development of hot spots.
Aggregate distribution of codling moths in orchards requires that population monitoring occur, with traps being located evenly throughout the orchard to ensure that hot spots are not being missed. Areas of high density won’t be impacted by mating disruption, and insecticide may be warranted in these locations.
There is only one pheromone that plays a role in codling moth mating behavior, and it is primarily made of an alcohol, with only 1% of its chemical makeup being an acetate. As mating disruption is increasingly utilized for codling moth control, is there concern that resistance could develop?
Research conducted in 2018 used the chemicals extracted from the glands of female overwintering codling moth larvae that had just pupated, which were then blown over male antennae. The experiment demonstrated that the male moths are attracted to the codlemone exuded, and that the codlemone collected from the female glands has not undergone any changes and is the same chemical configuration it always has been. These females also weren’t emitting any more of the codlemone, or a stronger formulation. “It’s still the same codlemone and there’s no indication of any change to the pheromone that it uses. And there also isn’t any change in the amount of the pheromone being emitted,” Thomson said.
Although it doesn’t appear that mating disruption is causing any changes in codling moth pheromones, proper use of mating disruption is imperative. “Making sure we have low populations by using pheromone properly, in conjunction with the insecticides we have, and good supplemental controls like sanitation … is really important for us to maintain good control of codling moth in the future,” Thomson said.