About the series “Warm Front” examines the ways that climate change is altering Minnesota and its landscape. Part 1: Spring trends earlier on the Rainy River Part 2: Invasive grasses choke birds’ habitat Part 3: Warmer lakes affect cold-water fish Part 4: Increasing rainfall overwhelms stormwater systems Part 5:: Invasive insects threaten Minnesota agriculture

Raspberries used to be an easy cash crop in Minnesota. Just plant, water, fertilize and "let it go," according to grower Ryan Femling in Afton.

That all changed in 2012, when the spotted wing drosophila showed up. The exotic fruit fly with big red eyes likes raspberries, pierces the fruit with its serrated appendage to lay its eggs inside. Upon hatching, larvae feed on the fruit and turn the berries mushy.

Femling, a specialty crops manager at Afton Apple Orchard, had to rip out several acres of infested bushes when the pest found his operation a few years ago. Now he sprays pesticides at night about once a week.

The spotted wing drosophila is just one of several destructive invasive insects, weeds and diseases moving in on Minnesota as climate change brings warming winters, longer growing seasons and increased rainfall.

To the general public, these invasive insects may be most obvious in their destruction of trees: Eastern larch beetles have decimated stands of tamaracks, and the emerald ash borer has ravaged city canopies.

But the damage to agriculture could turn out to be just as serious. The drosophila cost growers $2.4 million in crop losses and spraying costs in just one year and quickly forced some Minnesota fruit orchards out of business, according to a recent study. Some produce operations might be forced to install elaborate netting and other costly techniques to protect their crops. And farmers are on alert for another invader, the brown marmorated stink bug, which caused "catastrophic damage" to the produce harvest in several mid-Atlantic states in 2010, according to the University of Massachusetts Amherst.

The pest detection unit at the Minnesota Department of Agriculture is busy trapping insects, disseminating information to growers and monitoring bugs intercepted at U.S. ports and those marching toward Minnesota.

"There's always something new on the horizon," said Angie Ambourn, the unit's supervisor.

The spotted wing droso­phila and the brown marmorated stink bug are two of the "Big 3" invasive insects worrying the state's specialty crop growers, according to University of Minnesota entomologist Bill Hutchison. The third is the Japanese beetle and, taken together, they're already a threat to the state's small berry crops, wine grapes, apples and farmers market vegetables, Hutchison said. In time, they could also threaten soybeans and field corn, Minnesota's dominant cash crops.

The spotted wing drosophila made its unwanted appearance in Minnesota in some wild raspberries in 2012. It spread quickly across the state. A tiny brownish fly with a black dot near the tip of its wing, it favors the soft flesh of the raspberry, but most fruit is potentially a target, Hutchison said.

"It really likes to hang out at wooded edges around farms," he said.

University researchers are also studying the more familiar Japanese beetle. While not new to Minnesota — it showed up in the late 1960s — the beetle has flourished in the Twin Cities metro area with warming winters, Hutchison said.

A major landscape pest, the brown and metallic-green creature feasts on more than 300 species, including roses, grapes, apples and linden trees. It chews leaves around their veins into lacy skeletons, though it doesn't necessarily kill the plant.

It's largely been confined to the metro area and southeast Minnesota, but there are now reports of the beetle in row crops, where it can reduce yields, according to the Agriculture Department.

Photos by Brian Peterson and file

Minnesota's “Big 3” invasive insects: The spotted wing drosophila, top, lays its eggs inside fruit, and the larvae hatch and feast on it. The Japanese beetle, above left, feasts on more than 300 species, including roses, grapes, apples and linden trees. And the brown marmorated stink bug also has a wide-ranging appetite.

'It sounds like frying bacon'

Warming winters, longer growing seasons and wetter weather all make Minnesota more hospitable to the pests. According to the Minnesota climate office, the state's winters have warmed an average of 1.2 degrees Fahrenheit per decade since 1970.

For the stink bug and drosophila, both of which overwinter as adults, the milder winters simply mean fewer die off.

That's of less importance for the Japanese beetle, which overwinters as larvae in the soil, where it's cozier, explained Eric Burkness, a researcher in Hutchison's lab at the U. But Minnesota's wetter climate is giving the beetle a boost, he said.

"That increased rainfall allows the larvae to survive better as they're feeding on grass roots in the soil," Burkness said.

Irrigation systems are a "dinner bell" for the beetle, said Faith Appelquist, an arborist at St. Paul-based Tree Quality. New housing developments often see such a Japanese beetle frenzy of munching around July and August that she can hear them at work in the trees.

"It sounds like frying bacon," Appelquist said.

The brown marmorated stink bug — flat and pale brown, with white speckles — derives its memorable name from the penetrating coriander-like odor it emits through its abdomen when threatened.

U entomologist Bob Koch first discovered the bug in the state in 2010 when he stumbled upon one in a lab.

"I think it was probably brought in by some packages that came in, or maybe it was on somebody's shoulder," Koch recalled. "This insect likes to act like a stowaway — tuck in nooks and crannies."

Today, for reasons unknown, the stink bugs have congregated around Wyoming, Minn., where for now they're mainly an annoyance, said resident Lucy Stoyke. Stoyke said her daughter, Kristina, first spotted the bugs in the house. Now they are a family of citizen scientists, monitoring and collecting the insects, and storing them in plastic bottles they provide to U researchers.

The bugs have been particularly prolific this year. Last month Lucy Stoyke found a huge cluster in their lilac bushes: "There were so many in the lilac branches that I could just shake them."

The stink bug, too, has a wide-ranging appetite. It feasts on apples, raspberries, sweet corn, soybeans, green beans — even shade trees — piercing fruit with its needlelike proboscis and sucking out the juices.

Now it's turning up in some soybean fields, although it has not resulted in serious crop yield losses yet. "I think the key word is 'yet,' " said Koch.

David Kee, director of research for the Minnesota Soybean Growers, called it a "hungry beast" and said the state's farmers are "vigilant."

Mark Vancleave, Star Tribune

Ryan Femling sprayed his raspberry plants at Afton Apple Orchard in Hastings to kill the spotted wing drosophila, an invasive fruit fly. He spreads the pesticide after dark to minimize harm to bees and other pollinators.

Not a lot of good options

About once a week at Afton Apple Orchard, Femling sets out at sunset, steering his small sprayer tractor up and down the rows of red raspberries in the dark, when the fruit fly is most active and desirable pollinators are not.

His two tractor headlights float above the rows as he sprays a fine mist of pesticide during the height of the fall berry season.

A family-run operation, Afton Apple Orchard considered organic options such as covering the plants in high houses, he said, but it didn't pencil out. They opted to spray chemicals as carefully as possible. U-pick raspberries are part of the "agri-tainment" mix the farm uses to stay afloat.

"We'd be poor, broke and starving if we just did apples," Femling said.

Like Femling, other growers and gardeners have to make tough choices to keep the invasive bugs under control. Common insecticides can be effective but have unintended environmental effects. Growers using them are urged to spray only at night.

Organic insecticides such as spinosad and pyrethrin are available but aren't as effective.

The best nonchemical control option for all three of the "Big 3" insects, Hutchison said, is covering rows of plants in a fine mesh insect netting, a technique known as high tunnels.

It's not perfect, said Burkness, the U researcher. It's relatively expensive and "a completely different production practice."

"It's been a tough run," he added. "There hasn't been a lot of really good options."

Jennifer Bjorhus • 612-673-4683