Department of Plant and Soil Science
'Super Pests' Call for 'Super Solutions'
Yolanda Chen asks, What have we done to plants? and How do insects become pests?
- By Cheryl Dorschner
The history of one of our food staples – potatoes – is fraught with famine, blight and beetles. And another important food family – the brassicas – broccoli, kale, cabbage and Brussels sprouts are magnets for so many pests that they are routinely grown under row covers.
These two vegetables, like all agricultural crops, live on borrowed time – that is, until they are discovered by insect pests that are able to exploit them.
For some insect pests, each insecticide is effective for a limited time, for others, no insecticides are effective. None.
University of Vermont insect ecologist Yolanda Chen makes it clear that pesticides are never sustainable as a long-term solution.
“Some insects, such as the Colorado potato beetle, have evolved resistance, more than 50 times. The cost of pesticide research and development alone can be prohibitive,” she says. “The problem is that we do not understand how insects are able to do this over and over again.”
Chen’s current research studies two insects that attack potatoes and brassicas – the Colorado potato beetle and the Swede midge respectively.
The Colorado potato beetle, Leptinotarsa decemlineata, devastates crops in the Eastern United States and is problematic throughout the northern hemisphere. The beetle has been an extraordinarily successful pest, rapidly evolving pesticide resistance and adapting to changes in climate and its host plants. Chen’s lab is precisely focused on trying to understand why this beetle is so successful, and how it has evolved.
The Swede midge, Contarinia nasturtii, is a small fly whose larvae distorts the growing tips of plants. One cannot see the damage until it’s too late, and the crop has been destroyed. As a new arrival to Vermont in 2006, it is particularly devastating in the Northwestern corner of the state. This spells trouble for Vermont agriculture, because brassicas are ideal for Vermont’s short, cool growing season.
Chen looks for solutions by asking questions about the very nature of the role of insects in their environment. She asks, “What have we done to plants? How do insects become pests?”
ORIGIN OF THE SPECIES
“Most crops we grow in the U.S. are not originally from here,” Chen points out. “Potatoes originated in Peru. Brassicas originated in the Mediterranean region. We have moved them outside their native habitat to one in which they didn’t evolve in balance with predator and beneficial insects, fungi, bacteria and the like. Domestication reduces diversity and disrupts species interactions.” When relocated, their role in the system is completely changed.
That’s what we’ve done to plants. She also studies insects in terms of their origins. “If you think about it, 80 million years ago, all the major insect groups were already here on earth,” Chen says, “but agriculture has only been around for 10,000 years. So insects have a leg up, so to speak, on farm crops.”
Her research searches for the ecological and evolutionary origins of insect pests.
So for the Colorado potato beetle, “We looked at the characteristics of different populations around the world to understand how that beetle colonized potato crops,” she says. “We found one population in Mexico that shares many characteristics with those of northern U.S. populations – although genetically they’re different, they overwinter and they feed on the potato plants.”
Chen compares how beetle populations are genetically related, how they vary in response to the cultivated potato versus their native host plant Solanum rostratum, and whether different populations differ in their ability to become resistant to insecticides.
“What we learn about beetles in Mexico could provide insight about why this pest is so successful in escaping its natural enemies and adapting to temperate potato agroecosystems,” she says.
For the Swede midge, one study aims to increase the profitability of brassica farmers by developing low-input management strategies. Another looks at disrupting the host location using companion plants and non-host plant phytochemicals. But the larger question is still, how do we deal with invasive pests?
“If we understand more about insect ecology, we can exploit its ecological interactions for pest management,” Chen says. These new approaches to agriculture may lead to new methods ways to farm within a globalized world.
COMING TO A FARM NEAR YOU
Andy Jones has been battling the Swede midge in Burlington since 2010. For some reason the Intervale Community Farm, which he manages, seems to have been a pioneer in facing the problem, so he’s highly motivated to test solutions. “I was the grower who was driving forward the Swede midge problem for small, diversified growers. Nobody else was afflicted, and nobody else was interested, says Jones. “We are suffering! We’ve come to accept a lot more damage than we’d like in many of our Brassica crops.”
He and fellow farmers have experimented with row covers, netting, distant crop rotation and planting later so plants mature out of sync. with the midges’ life cycle. All of these increase costs, reduce yields or come with other issues.
“So if we can increase the plant’s natural defenses or somehow else reduce the damage through one of the experimental treatments, I would be very excited,” Jones says.
The Intervale Farm became a research site for Yolanda Chen in 2010 to try experimental sprays and row covers. Obviously there’s no quick fix, but the scientific information gathered is valuable.
“I think looking at any insect pest with an agroecological approach is worthwhile, Jones concludes. “As a lover of learning and science, I think that there are amazing things to be learned about our ecosystems, insects, our farms and nature. As a practitioner looking for sustainable management options, I am always pushing for research that has in-the-field relevance… some agroecological approaches have yielded great dividends for growers. Some have not.,” he says. “Ever the optimist, we will continue to work with Yolanda on this project as long as there is still much to know.”
Yolanda Chen is a scientist and an optimist. “If we understand more about insect ecology, we can exploit its ecological interactions for pest management,” Chen says. There are actually an increasing number of examples where scientists have "cracked the code" and been able to ecologically manipulate insects. These new approaches to agriculture may lead to new methods ways to farm within a globalized world.