Mar 4, 2011

Researchers testing disruption devices

Since the first commercial pheromone devices for disrupting moths became available in the early 1990s, thousands of U.S. apple growers have been using these devices. In Washington state, between 80-85 percent of apple growers use mating disruption devices, said Jay Brunner, a research scientist at Washington State University.

“This is up from about 60 percent of the growers in 2000,” Brunner said.

New types of mating disruption devices might be making their way to the market within the next few years, devices designed for dealing with a variety of pests.

Codling moth is an especially key pest in apples, since 0.5 percent damage is enough to disqualify an apple from the export market, Brunner said.

“And if you don’t get good control, you can end up getting as much as two or three percent damage,” Brunner said.

Mating disruption devices have become increasingly more important in controlling codling moth over the past five years, since organophosphates like Guthion have been getting phased out of the market.

“It seems like the technology has done well because the reports we’re getting back show that codling moth damage in the fields hasn’t increased and that, if anything, the damage has actually decreased,” Brunner said.

The way mating disruption technology works is that when synthetic sex pheromones get released from dispensers in the field, the pheromones attract male moths seeking fertile females. The males get disoriented by the pheromones and are unable to find female moths and mate. This means the moths can’t reproduce and eventually the moth population diminishes.

This technology tends to work best with relatively low populations of moths, Brunner said.

“If you have a high population, you can use pheromones plus an aggressive insecticide to control the moths. Then, after a year or two, you can dramatically cut back on the number of sprays.”

Most pheromone-based mating disruption devices are enclosed in plastic or synthetic polymers that get diffused over three to six months. Generally, growers hang 400 devices per acre at a cost of $125, which is relatively inexpensive compared to using multiple insecticide sprays. Researchers have been looking at other ways of dispersing pheromones, including spraying pheromones directly on the crop. So far, direct sprays have proved unsuccessful.

Another approach, which could reduce labor costs, involves using an aerosol pheromone-emitting device; i.e., a puffer, which would be dispensed at a rate of one or two puffers per acre. The aerosol emitters release large amounts of pheromones at regular intervals. While these puffers seem to work well in some situations, researchers are concerned that it might take too much time to monitor these devices to make them cost-effective.

“The puffers are relatively new technology, and the concern is that if you have one per acre, there could be gaps in coverage with the pheromones and the moths could end up mating,” Brunner said.

At Michigan State University, researchers have been looking at what attracts male moths to synthetic pheromone devices and how long the disorienting effects of these devices last. A lot of a moth’s response depends on its specific biology, said David Epstein, an MSU researcher.

Oriental fruit fly, for example, is easy to disrupt using straight mating disruptions, while other pests such as codling moths and borer insects are more difficult to confuse for long periods of time.

Matt Grieshop, another MSU researcher, is studying the possibility of using attract and remove technologies, whereby moths get attracted to a synthetic pheromone and then killed by an insecticide that gets released when the insect touches the pheromone device.

Basically, growers know they can confuse male moths for a while and keep them away from the females by using these synthetic pheromones. But the question is: How long do the male moths stay confused?

“From the standpoint of college kids, if a guy goes out to a bar one night and gets shot down, he may come back another night and not get shot down,” Grieshop said. “With the (moths), you can confuse them for a little while, and then maybe they’ll fly off to the next fertile female. But if you trap and kill them, they’re no longer playing the mating game.”

Part of the challenge in building a prototype for these attract and remove devices is getting the male moths to make physical contact with the devices. Certain insects, like peach tree borer, tend to crawl all over the dispensers in the right circumstances. Other insects, like codling moth, are more likely to keep their distance.

“What we found is that the codling moths don’t like very much of anything,” Grieshop said. “With the lesser peach tree borer, they like globular, high-contrast things, whether it’s a scaled model of a female made out of wire with clear plastic wings or an actual pheromone (dispenser) spray painted jet black.”

Whether growers use “attract and remove” strategies or straight pheromones, it helps to understand the insect’s specific biology, said Epstein, who has most recently been studying dogwood borer. More growers have been planting high-density apple orchards lately, which are highly susceptible to dogwood borer. Typically, the female dogwood borer chews her way through the soft bark, where the rootstock is grafted to the scion, and feeds on the vascular tissue of the tree. These pests are usually a problem for trees between the ages of three and seven, Epstein said.

“Dogwood borer is a tough one. It only has one generation a year and it’s a very strong flying insect. It lives longer than a codling moth does and it flies for a longer period of time,” Epstein said.

Until recently, the specific sex pheromone for dogwood borer was unknown, and growers were obligated to use sex pheromones from related species.

“Now we have a specific pheromone, and for the first time we’re working with a dispenser that has the right blend of the pheromone, which we’ve been field testing,” Epstein said.

Epstein is working with using straight mating disruption devices, as well as attract and remove strategies.
It’s too soon to tell for sure how well the new mating disruption product will work, Epstein said.

“It’s very early in the research, but from our 2009 studies, we saw fewer larvae in the trees where we did the mating disruption, and even fewer larvae in areas where we did attract and remove,” Epstein said.

By Lisa Lieberman