In sterile insect release, male insects made sterile by exposure to gamma radiation are released in huge numbers to compete with normal wild males. When the sterile males win the mating game, females lay infertile eggs.
In mating disruption, female sex hormones are released in such volume that males can’t find females hidden in the overwhelming flood of perfume, so females go unmated and can’t lay fertile eggs.
In both cases, reproduction is disrupted as infertile eggs fail to produce larvae that can infest and feed on their hosts.
In British Columbia’s Okanagan, Similkameen, and Shuswap valleys, the two methods are in the second year of a three-year test comparing their effectiveness. It’s a huge test covering more than 4,000 acres of apples in each method.
Dr. Gary Judd, an entomologist and research scientist at the Pacific Agri-Food Canada Research Centre in Summerland, said sterile insect release began there in 1992, and after 20 years it has been effective—but somewhat expensive.
“Overall, it has been highly successful,” he said. “Codling moth numbers have been so reduced that on half the acreage, almost nobody sprays for codling moth.”
The program initially was conceived as an eradication program, and while it reduced codling moth numbers greatly, it was not able to achieve eradication. So it evolved into an annual management program.
“It worked best in the area close to the U.S. border,” Judd said. “At the north end of the valley, it didn’t work as well. Growers there began to use mating disruption as well, but that greatly added to their expense. So the next step is to compare the two and perhaps choose one.”
During the test, the cost is the same for all growers. The management team, which operates the Okanagan Kootenay Sterile Insect Release Program, also provides everything needed for the mating disruption program.
In a deal that goes back to the start, the costs of the SIR program are split 40-60 between growers and property-owning taxpayers, said Cara McCurrach, who heads the team.
Growers pay $139 per acre of apples, pears, or quince they grow, every year. Urban and suburban property owners in the district pay a fee based on the land value of their property, which McCurrach estimates amounts to about $11 a year for an average property. The money goes to hire people to deliver the areawide program—about five full-time and 30 seasonal people who work in the orchards—plus nine permanent staff who operate a sterile moth production factory at Osoyoos. The Canadian government built that facility in 1993, at a cost of $7.4 million.
Lots of politics
Despite the achievements of the sterile insect releases, the program is fraught with the kind of political problems McCurrach believes surrounds any areawide program that depends on the cooperation of lots of people. Here are some of the issues she noted:
Declining fruit base—When the program began 20 years ago, it covered 22,000 acres, but now covers 8,500. Why? The British Columbia fruit industry has not been doing very well, for several reasons, so growers are leaving the business. The costs of the program have remained the same over the past three years, so, with the reduction of planted acreage, the burden of paying for the program falls on fewer and fewer growers.
Lofty goals—The goal in recent years has been to reduce the level of codling moth damage to less than 0.2 percent at harvest on 90 percent of the acreage, and that has been achieved. But for reasons not easily explained, growers operating about 10 percent of the acreage continue to experience “hot spots” where damage is higher.
These growers pay their share of the SIR cost, but have to buy insecticides and spray as well. “We work very hard with them to bring them to the same level of control,” McCurrach said.
Over enforcement—The legal structure that set up the sterile insect release program in British Columbia gave workers in the program rights to enter and monitor private property, which was not always popular. The program began with a “heavy cleanup” campaign.
All host trees
There were efforts to locate all host trees in the valley—in orchards and in cities—and to coax homeowners to remove trees or manage them. A tree-banding program is still under way to capture and destroy pupating codling moths.
The program is governed by a board made up of local government and industry stakeholders, and experts like Judd serve in advisory capacities, helping with the project design and solving problems.
In general, McCurrach said, homeowners support the program because the fees are small for each household, and they see the benefits of less spraying and less pesticide in the environment. “There was not a lot of pushback from homeowners,” she said.
Early in the program, growers were more resistant—until they started to experience a reduction in codling moth infestation that translated into a reduction in their spray costs. Most then became more enthusiastic about it. Unfortunately, a rise in the overall production costs for the area’s tree fruit industry and some areas where the areawide controls seem to have a less-than-perfect effectiveness continues to pressure the program with a pushback from growers in the northern end of the valley.
Mating disruption alternative
In the effort that began in 2011, growers in the northern end of the valley, where the areawide program has been less effective, are testing mating disruption as an alternative to SIR. Growers in the southern end, who are much happier with the program, continue to get their weekly allotment of sterile codling moths—1,000 per acre each week. At the height of the program, more than 12 million sterile moths were released every week.
“Our staff does all the weekly sterile releases and hangs all the mating disruption dispensers. Consistency in application of the control measure is a key element of areawide pest management,” McCurrach said.
One task they also do is surveillance and monitoring of the pheromone traps placed to evaluate the program’s effectiveness. Every week in every orchard, they monitor the traps, squashing each of the moths captured on the sticky glue trap bottom liners, looking for “pink guts.” The sterile moths are all reared on a special diet that contains a red food dye, so any moth that doesn’t look red when squashed is a wild one.