Tree Fruit & Grape News, March 1999

Mating Disruption of Codling Moth

Gary J.R. Judd
Pacific Agri-Food Research Centre,
Agriculture and Agri-Food Canada, Summerland

In 1992, I wrote an article for the British Columbia Orchardist (Vol. 15(3):13-15) entitled, "Management of Codling Moth with Pheromone: a new twist in insect control", in which I discussed how effective this new technology was, and how a small group of organic apple growers in Cawston were leading a successful charge into a new era of insect control.

Unfortunately, that was the same year the Okanagan-Kootenay Sterile Insect Release Program, better known as SIR, received funding to build the rearing facility in Osoyoos. As a result of the SIR initiative, interest in the control of codling moth with pheromones was low, but I continued to speak to various growers’ groups explaining to each that this was "what everybody else would be doing". By everybody else, I meant our American cousins. History has proved me correct as in Washington State (WA) alone, 57 thousand acres of apples were treated with pheromones to control codling moth in 1998.

What are pheromones?

Pheromones are natural chemicals, usually produced by the female of a species to communicate and signal her presence to potential mates. Based on this normal biological function, pheromones are quite simply defined as, chemical sex attractants. The existence of pheromones has been known to entomologists for over 30 years, and codlemone, the major active ingredient in the codling moth sex pheromone, has been known for 25 years. Scientists have developed methods of synthesizing pheromones in the laboratory, and many are readily available for commercial use. For over a decade, many growers have been using synthetic codlemone in traps to monitor male codling moth populations and time insecticide sprays.

How can pheromones be used to control insects?

When sufficient synthetic pheromone is released into the air within an orchard, male codling moths become confused, and are unable to find females. When normal chemical communication between male and female moths is disrupted, mating is disrupted, fewer fertile eggs are laid, fewer larvae hatch and less damage occurs. This entire process is commonly called "pheromone confusion" or "mating disruption" (MD).

There are several ways excessive pheromone confuses male codling moths. Firstly, male moths follow the false pheromone trails created by the release of synthetic pheromone into the wind, thereby making themselves unavailable for mating. Secondly, male moths exposed to high concentrations of pheromone become so desensitised to pheromone that they no longer smell it, or respond. Normally, an insect’s nose, that is it’s antennae, detects the pheromone and sends a message to the brain. However, after long exposure to pheromone, neither the antennae nor the brain respond; this is known as habituation. Thirdly, the highly concentrated synthetic pheromone trails released from dispensers, mask or camouflage, the weaker, natural pheromone trails of female codling moths.

Applying pheromones

Various systems for applying and releasing synthetic pheromone into an orchard have been devised. One of the simplest, and the one that is registered in Canada and currently being used throughout Washington, is a reddish brown plastic dispenser that looks something like a garbage bag "twist tie" (Fig. 1). This dispenser also known as a Shin-etsu Rope, is sold under the trade name ISOMATE-C+ (South Valley Sales and Growers Supply). The Isomate-C+ dispenser is a hollow, sealed tube that contains about 200 milligrams of liquid pheromone. Upon exposure to warm air or sunlight the dispenser heats up and pheromone is released as a gas through the plastic wall of the tube. When numerous dispensers are releasing pheromone into the air of an orchard they create a cloud of pheromone. In order for MD to be effective, the pheromone cloud must be maintained above a critical concentration during variable weather conditions for several months. Years of research have been spent developing release devices to achieve this objective. Pheromone must be applied before codling moth begin to fly and mate in the spring. This means that the pheromone dispensers are usually applied in late April or early May, depending on the temperatures in your area. Pheromone dispensers must be fastened to lateral branches near the top of the tree, usually in the top third, on strong branches that will not hang low when fruit are present. In old standard plantings this can require a ladder to hang dispensers, although some inventive American grower has built a special tool on a pole to attach them without a ladder (pheromone retailers should be able to provide these).

Research has shown that one spring application of 400 dispensers per acre is sufficient to provide season-long control of codling moth in B.C. We know from many experiments over the last 10 years that applying more than 400 dispensers per acre does not improve control, it is just a waste of pheromone and money to treat at levels above 400 per acre. The 400 dispensers are distributed evenly throughout the orchard. For example, if an orchard has 400 trees per acre then every tree should have one dispenser. In addition, the density of pheromone dispensers should be applied at a double rate (equivalent of 800 per acre) along the border trees. Therefore, each edge tree in our example should receive two dispensers. Research has shown that codling moth can be controlled with 200 dispensers per acre, provided population densities are low, applying one cover spray of Guthion during the first flight of wild moths ensures populations are low. Pheromone should always be applied first and then the spray, do not wait until you spray to apply pheromone.

How well does pheromone confusion work?

In 1990 we began using MD on a small scale with five organic growers in Cawston. They have continued to use MD to this day, most recently in combination with SIR, but earlier in combination with tree-banding to catch overwintering larvae because they could not use Guthion to reduce starting populations. Research has shown that as much as 50-60% of the overwintering codling moth population can be removed and destroyed using banding techniques. Table 1 summarises the levels of damage seen in these pheromone-treated orchards over the last 10 years. Some comparison orchards receiving Guthion sprays (1990-1992) or in recent years Guthion sprays and SIR (1995-1998) are also shown. It is very clear that the combination of MD and SIR is a very powerful control strategy. Our experiences here have been mirrored by a similar, but larger trial (600 acres), in Oroville, WA. Table 2 shows results provided by the USDA, at Wapato, showing a significant reduction in damage and populations of wild codling moth by using a combination of MD + Guthion in the early years and MD + SIR more recently.

Limitations of pheromone confusion

Our research has shown that when disruption fails to control codling moth damage below an economic threshold (1.0%), this lack of control was correlated with one of several factors: 

1) Experience has shown that MD like SIR, works best when initial codling moth population densities are low. As a general rule, MD as a stand-alone tool is not recommended when codling moth damage was greater than 2% in the previous year. However, we have shown that higher populations are not a problem if good orchard sanitation precedes pheromone treatment, or if growers apply one cover spray of Guthion at the correct time during the first flight of the season. 

2) MD has not worked as well in orchards with trees taller than 12-15 feet, unless you also apply a cover spray. We know this is related to the larger canopy volumes in larger trees, which simply means more pheromone is required in taller trees, or a lower population to start with. It is more effective to apply a cover spray than it is to put out more pheromone. 

3) Orchards or blocks to be treated with pheromone should be larger than one acre to lower the chances that mated females will fly in from neighbouring trees. Remember, MD of moths in your orchard, will not control mating of moths in your neighbours orchard! The best thing to do is to have several growers in an area treat with pheromone, this area-wide approach is being used successfully in Washington State. In areas being treated by SIR there is no need to worry about immigration of moths into a small orchard because chances are that moths entering your orchard will be sterile. 

4) MD will not work in a backyard setting with very few trees because the pheromone cloud I referred to earlier is created by having a dense uniform tree canopy. Therefore, orchards with many missing trees or open spaces and variable canopy heights are not good sites for MD. 

Summary. The major limiting factor to successful use of MD is population density. If initial populations are low enough, most of the problems listed above become unimportant, so everybody should apply that first cover spray the first year they use MD. In the second year of use the spray will probably not be needed.

Who is or should use MD for control of codling moth?

MD will continue to be used by organic growers throughout BC and the rest of the world, but more locally, conventional growers who have not seen their codling moth counts come down under the SIR program should most definitely use this new tool. Growers in Zones 2 and 3 of the SIR program should look to use MD disruption in combination with their current Guthion controls, just to ensure they have low populations of codling moth when SIR comes to their area.

Availability of codling moth ISOMATE-C+ in Canada

Isomate-C+ is the only registered pheromone product available for control of codling moth in Canada, it can be purchased through regular chemical retailers or through contact with the SIR program staff in Osoyoos. Applicators for applying Isomate-C+ should also be available through these same outlets. More information on using Isomate-C+ should be available from the SIR Program staff.

Future research on MD

The success of mating disruption research in WA and elsewhere, indicates that pheromone confusion, as a method of controlling insects, is here to stay. An application rate of 200 Isomate-C+ dispensers per acre at a cost of about $75 CDN for the product and one hour of labour to apply, makes MD cost competitive with conventional insecticides. Research in 1999 will examine for the third year the effectiveness of a MD product, ISOMATE-CM/LR that will control codling moth and leafrollers at the same time. This product will bring down the cost of insect control substantially. In addition to our work on codling moth, we are currently conducting mating disruption research on eye-spotted bud moth and mullein bug among others. We hope our ongoing research will make the production of insecticide-free fruit a reality for many local growers in the not too distant future. 

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