The sting thing

Farm Forum

Are you bugged by a munching, gnawing, tree- or crop-decimating, even cattle-annoying, insect?

It just happens that there is probably a wasp for that.

Wasps have a reputation of being indiscriminate stingers of anyone who happens to pass. But the wasps best known for daubing mud, building paper nests hanging in the patio, or swarming from an underground lair are few in number compared to the wasps that are increasingly being used as a biocontrol agent in the protection of agricultural crops – parasitic wasps that prey on such pests as the alfalfa weevil that damages hay fields, emerald ash borer that kills ash trees, whitefly that attacks greenhouse tomatoes, even biting flies in livestock pens.

And the best thing about these wasps: they don’t sting humans.

Just as good, parasitic wasps do as their name implies: The adult female stings her host and lays her eggs inside the host’s abdomen. The wasp larva hatch and consume the host from the inside, leaving the host’s dead body to pupate into adults.

Parasitic wasps are very specialized in which hosts they select and are very effective at controlling that host’s numbers. They are a very real way to decrease the use of pesticides without sacrificing crop yield. Frank Stonaker, pest management advisor for Colorado Greenhouses near Denver, says that biocontrol is about 25 percent less expensive than using pesticides and can be just as effective, without the damage to the beneficial insects and environment that chemicals have.

“In areas where three or more parasitic wasps are established, alfalfa weevil is seldom of economic importance,” agreed Anthony Shelton, professor of entomology at Cornell University in Ithaca, N.Y., “even in areas once requiring multiple applications of insecticide.”

However, parasitic wasps have had limited use as a widespread pest control because of a lack of efficiently producing populations of the wasps.

Piet-hein van Baar, manager of Willcox Greenhouses in Willcox, Ariz., worked with the University of Arizona and the USDA in using parasitic wasps to control greenhouse pests. He says he was impressed by how little pesticide needed to be used, and if not for timing difficulties with wasp releases, he might not have needed to use chemical at all.

Shelby Fleischer, entomologist at Penn State University in University Park, Pa., adds that orders of biocontrol insects need to be made well in advance and producers do best if they know exactly how many they need which weeks. The progress isn’t flexible enough to allow producers to adjust releases according to regular monitoring of their crops.

That’s why a team of researchers with the U.S. Department of Agriculture has been working on ways to stockpile a certain species of parasitic wasp, Habrobracon hebetor, that attacks the Indianmeal moth – the insect that attacks stored grain products, including bagged flour and boxed cereal in household kitchens. These moths not only cause product losses, but even in small infestations where their effect on stored food isn’t noticeable, they can leave behind contaminants.

USDA studies indicate that releases of the H. hebetor wasp can reduce Indianmeal moth populations by 71 percent, or by as much as 97 percent if H. hebetor is combined with another parasitic wasp that targets the moth’s eggs.

H. hebetor adult wasps can be conditioned to remain in a resting state through two months at 41 degrees Fahrenheit and then be revived without ill effects. According to James Throne, research entomologist at the USDA’s Center for Grain and Animal Health Research in Manhattan, Kan., this cold-storage technique could open the door for wasp-rearing operations to go commercial by increasing flexibility of wasp releases and reducing the expense of maintaining wasp colonies between releases.

If the research continues to hold promise, this could significantly upgrade the use of parasitic wasps as a biocontrol industry-wide.

That’s what Helmuth Rogg, manager of the Oregon Department of Agriculture’s Insect Pest Prevention and Management Program, is hoping. Oregon is battling a new, invasive insect threatening major agricultural regions, such as Willamette Valley.

“On a pest risk scale of one to 10, I would say the brown mamorated stink bug is a 15,” Rogg said. “Biological control can help. It’s a perfect choice for a classic, biological control program. We have an exotic pest that comes into a new environment without its natural enemies where it can easily multiply. Parasitic wasps are found in its native Asia and brought to the U.S. Hopefully, biocontrol will be successful, because there aren’t really any other viable management options at the moment.”