Wasps on the job
Not all wasps are jerks.
Some of them are good guys, and a particular kind of wasp has joined the ranks of beneficial insects being used to fight noxious weeds in the Grand Valley.
Now before you get all worked up over wasps being released on purpose, keep in mind these are not your run-of-the-mill yellowjackets dive-bombing your backyard barbecue.
This wasp has an important job to do in the war on weeds, and it doesn’t sting people.
Meet Aulacidea acroptilonica, the gall-forming wasp being released by biological control specialists at the Colorado Department of Agriculture’s insectary in Palisade. This insect comes from several places in the Middle East and southern Russia and has been studied since 2003 in Europe.
It was sourced by scientists looking for a natural biocontrol agent to introduce in the United States, spent some time at Montana State University in quarantine, and came to Palisade for additional study and release in 2013. Its target? Russian knapweed, a noxious weed on the state’s hit-list of most-wanted weeds.
The wasp joins the gall midge, another insect being used as a biocontrol for the weed, and works in a similar way but has different strengths, according to Joel Price, a biological control specialist at the insectary.
Experts have been releasing the wasp to see how it performs in the high-desert environment for the past three years, and have established it in Palisade outside the testing facility, as well as at sites in Whitewater and near Delta.
This year, officials released the wasp on Bureau of Land Management property near Loma, hoping that it will thrive on a large population of Russian knapweed and multiply.
The wasp works its magic slowly, but effectively, Price said.
The wasp damages the weeds in an ingenious way: by laying eggs in the stem of the plant. Then those eggs stimulate the plant to use energy to encapsulate the foreign object, making it harder for the weeds to use that energy for other things, such as growing and spreading or making seeds.
“These wasp larvae fool the plant into producing the swelling and nutritive tissue for the larvae,” Price said.
While the wasp doesn’t kill the plant quickly, it handicaps it and keeps it in check, so it can’t be as aggressive.
“Anytime a plant is forming additional structures such as a gall, it diverts nutrients that would otherwise go to flowers and seed production,” Price said. “Under certain conditions you can imagine that it can’t really afford that diversion and it can stress the plant and it reduces its competitive ability.”
Like other insects, the adult form of the wasp lives only a few days, and exists mainly for reproduction. The larvae is what really hits the knapweed hard, and it stunts the plant and can severely deform the stem.
The wasp has special strengths that make it a different and effective tool in addition to the gall midge, Price said. Because it has a hard-bodied exoskeleton, it can withstand more extreme conditions and isn’t as sensitive to weather changes as the midge. It also attacks the stem of the plant, while the midge prefers soft, new growth, and both insects are useful in doing their respective damage to the plant.
“If the plant were the human body, the wasp would be attacking the core,” said Price, and that results in reducing the plant’s growth more effectively overall.
The wasp prefers undisturbed patches of knapweed, while the midge thrives with more disturbance because it likes the soft, new growth on the plant, Price said.
Both insects are particularly helpful in reducing the spread of the weed, which has a habit of sprouting aggressively if landowners try to cut it down or pull it from the ground and leave broken bits of roots.
“I think of it as the head of the hydra – you slice one off and you get two,” Price said. “That’s why mechanical control is particularly challenging, and these little gall-formers can help slow it down.”
Right now, officials at the insectary are targeting areas they know are infested with Russian knapweed, and have the best chances for the wasp to succeed. The idea is to establish field nurseries, where they can go back and collect populations of the wasp and start distributing them more widely. This is a slow process, because the wasp only has one generation per year. Officials are working with a network of landowners and public-lands agencies to make this happen.
“In the next two years we hope to continue to facilitate their exponential growth across the state,” Price said.