Predators and other natural enemies need help to maintain and improve codling moth control programs.
Once-stable integrated pest management programs for apples, walnuts and pears in Western orchards began to show cracks as organophosphates fell out of favor.
The softer, more targeted products replacing them seem to affect orchard systems in less-clear ways, including outbreaks of previously controlled secondary pests, such as spider mites, aphids and pear psylla, says Vince Jones, entomology professor at Washington State University’s Wenatchee Tree Fruit Research and Extension Center.
Jones serves as director of a three-state team studying ways to improve codling moth programs through enhanced biological control.
“Secondary pests are easily managed by natural enemies—as long as we don’t disrupt the natural enemy cycle,” says Nick Mills, professor of entomology at the University of California, Berkeley.
While new pesticides may be less toxic to humans, “that doesn’t mean they’re low risk to natural enemies,” Mills says.
Subtle, longer-term effects
Standard pesticide studies look at outright mortality in non-target organisms, but may not catch more subtle, longer-term effects, Jones says.
Parasitic insects, spiders, ladybird beetles and other natural enemies may be suffering from long-term population reduction through pesticide-induced sterility, lower egg production or changes in sex ratios, Jones says. Pesticides also may draw out the kill time for some beneficials beyond studies’ 24- and 48-hour exposure windows.
“It’s not as bad as killing them outright,” says Peter Shearer, entomology professor and superintendent of Oregon State University’s Mid-Columbia research center in Hood River. “But if they’re not there in numbers to provide control, then they can’t get the IPM job done.”
Pear growers face greater difficulty with psylla, he says. Some products used against codling moth are toxic to psylla’s natural enemies, while early-season sprays of low-dose pyrethroids can build to dangerous levels over time.
Managing psylla through biological control would produce substantial reductions in spray costs, Shearer says.
Pesticides’ effects on natural enemies
Mills’ assignments revolve around walnuts, starting with lab tests of recently released pesticides along with those still in the pipeline. “We’re getting the start of an idea of which ones are likely to be most disruptive to natural enemies,” he says.
Rimon (novaluron) and Delegate (spinetoram), for example, seem to pose problems in the lab for natural enemies. Field tests starting later this year will attempt to confirm those results under commercial growing conditions.
Parasitic wasps that have reined in walnut aphids since the 1970s now seem to suffer disruptions from some of the new products.
Along with looking at sublethal effects on natural enemies, Jones and his team hope to develop better phenology models for natural enemies and spray strategies that minimize impacts on beneficials without sacrificing pest control effectiveness.
New monitoring techniques
That requires new ways to monitor target species, including finding the best attractants for lures. These new methods also will be “valuable additions to the toolbox” for growers and pest-control consultants, Mills says.
And because the natural enemies involved typically are found in many different crops, developments here could aid more than just tree-fruit growers.
But predators aren’t easy to study. “Unless you actually catch them in the act of eating something, it’s hard to say which is responsible for what,” Jones says.
Tom Unruh, research entomologist at the U.S. Agriculture Department’s Agricultural Research Service unit in Wapato, Wash., is trying to solve that problem with a two-pronged approach: orchard video cameras and gut-content analysis.
Producing sufficient solid data from the cameras has proved tricky, Unruh says, but he’s logged some surprising initial results.
“So far we’re seeing birds and rodents doing most of the work” when it comes to predation of codling moth larvae, he says.
The cameras also clarify the importance of the predatory ground beetles that orchard folklore holds up as a key codling moth predator. While the beetles zero in on moving larvae, they ignore the cocooned form in which the moth spends six months of its life, he says.
“We’re learning a lot,” Unruh says. “But it’s slow going.”
It’s what’s for dinner
Molecular analyses of what different predators are eating have run into hitches in finding a definitive process that’s not too sensitive for speedy use.
Bats also serve as natural enemies, with codling moth DNA detected in feces up to 18 hours after feeding. But many of the controls used in conventional orchards aren’t soft on birds and bats, he says.
Some growers have added plantings near their orchards that enhance bird and beneficial arthropod habitats, he says.
“We’ve made some good progress on the project,” Jones says. Lab and field research will remain the primary focus for the next two years, after which economic analysis and outreach will come to the fore. A how-to manual and scenarios to guide growers to the most cost-effective program will be integrated into WSU’s online Decision Aid System.
“We have to be able to show that it works on a commercial scale,” Mills says.
“We’re trying to leave a legacy of information that will be synthesized for various crop systems,” Jones says. “We want to have as good an online presence as possible that people can use.”
The end result, Shearer says, will lift IPM to a higher level that relies more heavily on natural enemies to regulate secondary pests.
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