War of the Species: Scientists Try Natural Enemies in Fight Against Harmful Pests

By Tina Lam, Detroit Free Press

Nov. 15–The sesame seed-sized milfoil weevil has its own fan club.

At Paradise Lake in northern Michigan, residents hold an annual Weevil Festival in July, dressing up in weevil costumes and holding street and boat parades to honor the critter.

An Ohio company that raises and releases the weevils, including in 50 Michigan lakes, sells a popular weevil plush toy.

Why the love? When planted by the thousands in lakes infested by the invasive Eurasian milfoil, the weevil larvae burrow into the plants’ stems, chewing away until weakened plants collapse.

Weevils, beetles, wasps and fungi are the new heroes in a David-and-Goliath battle. Scientists are unleashing them to attack invasive species that kill trees and dominate native plants, robbing wildlife of food and habitat.

“I don’t think people are aware that invasives are costing us billions of dollars every year,” said Carl Freeman, a professor of biological sciences at Wayne State University.

Because they are foreign, invasive species have no native enemies. Scientists search out their natural enemies, often in the invasives’ home countries, and bring them here. The goal is to use biological control instead of expensive chemicals or machine harvesting.

Consider the weevil …

“The weevils have been very successful for us here for 10 years,” said Marilyn Smith, president of the Paradise Lake Association near Mackinaw City. When the group first planted weevils, 340 of the lake’s 1,900 acres were packed with dense green mats of lacy milfoil weeds. Boats had trouble getting through and fish were disturbed. Once the weevils arrived, the milfoil retreated.

Marty Hilovsky calls his weevil program “bugs without borders.” He’s president of EnviroScience Inc. in Ohio, which raises Euhrychiopsis lecontei weevils and has planted them in 120 lakes in 10 states and Canada to tackle milfoil.

The weevils are native to the United States and Canada, but lakes usually have too few to damage milfoil. It takes huge numbers, raised in a lab, to do the trick. Because weevils aren’t cheap, their use can divide lakefront homeowners who often pay for the controls.

Kendra Cheruvelil, a Michigan State University freshwater ecologist, hopes to determine scientifically, not just anecdotally, whether they’re working.

Carol Plunkey, president of the Van Etten Lake Association in Oscoda County, said the weevils “are doing a great job.” The association stocked weevils for two years starting in 2003. “We were prepared to do it for five years, but we didn’t need to,” Plunkey said. “Cost was part of it, but it was an environmentally-friendly way to clean up the lake” without hurting fish or native plants.

… and the galerucella beetle

The galerucella beetle, native to Europe, gets credit for chewing up hundreds of acres of purple loosestrife, a pretty but destructive invasive plant that has taken over many wetlands and lakeshores in recent decades. Starting with about 22 experimental sites in the mid-1990s, MSU entomologist Doug Landis planted the tiny beetles. “It’s quite a dramatic success story,” he said.

The beetles caused severe damage to the loosestrife within four years. Now, the beetle planting has spread to hundreds of sites in Michigan.

Loosestrife is still around, but instead of being 6 to 8 feet tall and dominant, it’s a foot or so tall and grows in scattered spots, struggling to compete with native plants.

Landis said it often takes years and careful research to get approval to release foreign enemies to tackle invasive species. Scientists must show that they won’t cause extra harm by importing predators for the invasives. Sometimes, the foreign predator and prey continue to live together in balance, and in other cases, the imported enemy dies out when it kills off an invasive species, because it no longer has a food source.

Wasps vs. emerald ash borers

Leah Bauer doesn’t know yet whether the Asian stingless wasps she and other researchers released from August to October in Michigan forests will kill off the emerald ash borer, but she’s optimistic. Bauer, a U.S. Forest Service entomologist at MSU, has raised thousands of the tiny wasps that are natural enemies of ash borers in their native China.

The ash borer, first found in Wayne County in 2002, has no natural enemies here. Since its arrival, the borer has spread and killed more than 20 million ash trees, mostly in Michigan. In China, the tiny wasps keep the borer beetles in check.

The three types of wasps being tested in Michigan bore into the beetle eggs or larvae, killing them. The releases were in Ingham, Shiawassee, Genesee and northern Oakland counties. More releases will occur next year, and a lab may be built in Brighton to raise the wasps.

“We’re hoping to tip the balance of nature in favor of the ash trees,” Bauer said.

Fungi research on horizon

Wayne State researcher Freeman has a vision: Long, thin endophytic fungi, thinner than human hairs, weave through the inside of phragmites australis plants, an aggressive invasive species that can grow 15 feet tall.

He hopes to get funding to infect phragmites seeds with the fungi. The fungi live and spread inside the plant’s stem and prevent nutrients from getting to it. Bamboo-like phragmites grows so densely that turtles get trapped inside stands of it and die, fish can’t get enough oxygen, and ducks and red-winged blackbirds can’t nest there.

People have tried chopping phragmites down and burning it, but it comes back. Spraying chemicals on it takes five to seven years to work, Freeman said. Phragmites occupies millions of acres in the United States.

“What’s going to work in the long run is a bug or a nematode or a fungus that can attack it,” Freeman said.

Contact TINA LAM at 313-222-6421 or tlam@freepress.com.

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