Stink bug enemy breeding in lab
Parasitic wasps, chemical lures show promise to control pest population
Published: Monday, March 14, 2011
Updated: Tuesday, March 15, 2011 00:03
In a sealed-off, quarantined laboratory, Kim Hoelmer is cultivating a weapon. Inside a climate-controlled room protected by double thick windows is a colony of tiny parasitic wasps that have the potential to save the local agricultural economy from a foreign invader.
Hoelmer, a research entomologist at the USDA's Beneficial Insects Introduction Research Unit, which is housed at the university, says the wasps being studied here may one day control the population of the brown marmorated stink bug, an invasive species from China.
Stink bugs do not bite humans or carry disease. Instead, they wreak thier devestation on the local economy.
Last year, the brown marmorated stink bug ruined much of the fruit harvest in the Mid-Atlantic region, and some farmers reported that they had to throw away 20 percent of their apples. When stink bugs feed, their straw-like mouths bore holes in the fruits they eat. Although the scarred produce is not dangerous to eat, it takes on a corky texture undesired by consumers.
Without a natural predator in this area, the stinkbug population has grown exponentially. They were first discovered in Allentown, Pa., between 1996 and 1999, but now they can be found in 29 states.
"If we find out where these invaders are from, we can go there and find the natural enemies that keep them in check," Hoelmer says.
In 2005, when it became apparent that stinkbug numbers were on the rise, Hoelmer traveled to China and Japan to search for a natural enemy. Sometimes, native predators will prey on invasive species. However, this did not happen with the brown marmorated stink bug.
"The native natural enemies, the native parasites of stinkbug eggs, were not switching over to this invasive species," he says. "The next step was to go to Asia and look for natural enemies of the brown marmorated."
After a week of searching through the countryside, Hoelmer found what he was looking for on the back of a leaf—a cluster of stinkbug eggs, overtaken by the parasitic wasps.
The wasps, less than a millimeter in size, grow their young inside stinkbug eggs. As the wasp develops, it eats away at the unborn stinkbug. When the egg hatches, all that is left is the wasp. Stinkbugs lay their eggs in clusters of around 25, and a female wasp will inject her young into all of them. Every time a stink bug egg mass is found by a parasitic wasp, it will produce 25 more wasps, the females of which will then seek out stink bug eggs of their own.
"Theoretically one female wasp at the beginning of the season can produce thousands of wasps at the end of the season," Hoelmer says. "And each one of those wasps will have eliminated one stinkbug."
What he is testing now is whether these wasps will kill other non-invasive stinkbugs and beneficial insects in the area.
"We have to make a case that it will be safe enough to release; that's what most of our research is based on," Hoelmer says. "Until that time, it stays inside the quarantine lab."
It's imperative the wasps only kill the invasive stink bugs. Hoelmer says there are beneficial stink bugs in the area, and if the wasps attack those as well, it could disrupt the native ecosystem. Certain stink bugs are predators for other agricultural pests.
"We don't want it feeding on every stink bug, or attacking every kind of stink bug that it comes across. Because actually there are some beneficial stink bugs, people may not think about that," Hoelmer says.
So far, he says the wasps seem to have an affinity for only the invasive variety. Hoelmer says his testing is in advanced stages, but will still need approximately two more years of research before he can submit a proposal to take the wasps outside of quarantine.
Although the use of the wasps as a biological control seems promising, a solution two years from now offers no relief for local farmers. However, a more short-term solution may be in sight.
In Beltsville, Md., researchers at a USDA lab have synthesized a chemical lure for the invasive bugs. Insects communicate mainly by chemical sensors, and the right formula can trick male stink bugs into thinking they are following a mate. This lure, combined with a mechanical trap, could stabilize the pest's booming population.
Jeffery Aldrich, a research entomologist at the lab, has studied the chemical—a pheromone of another insect—since 2003. Aldrich says by this summer, there will be stinkbug traps on the market. He says researchers are still working on a stink bug repellent, but the chemical lure is a good start.
"We've got about half of the equation," Aldrich says. "I'm confident that people will see bugs in their trap."
He also says a spray that combines the lure with a poison could be effective in controlling stink bug numbers in orchards. Aldrich says the farmers would only have to spray a few of their trees. The bugs would be attracted to them and then die from the poison.
However, he's still searching for a true stink bug pheromone, which would be more effective than the chemical they are currently working with.
Stuart Constable, production manager of Highland Orchards in West Chester, Pa., says farmers are still in the dark about what they should do to combat the stink bugs.
"It's on the front burner, it's a hot topic," Constable says. "But we don't have any concrete answers."