Small insects no larger than a pinhead create an enormous predicament for Minnesota farmers: whether to use insecticides.

Because soy aphids – miniature fly-like insects that eat soy plants – arrived in the United States from Asia about three years ago, they have destroyed crops across the country. Because soy crops provide three-fourths of Minnesota’s livestock feed, a solution to the soy aphid problem is particularly important for state farmers.

University entomologist George Heimpel is working to help farmers prevent the damage without using chemical insecticides. Heimpel said he hopes to reunite the soy aphid with its natural enemies from Asia to solve the need for pesticides.

Heimpel said insecticides provide a temporary solution, but the effects are short-lived and bring other consequences.

“Spraying not only destroys the soy aphids but also its natural enemies,” Heimpel said. “What’s more, insects tend to become resistant to insecticides over time, and we have to continually develop new chemicals to kill them.”

Shortly after soy aphids began eating U.S. crops in 2000, Heimpel and two other researchers went to northeastern China to collect insects that prey on aphids. Since then, he has been testing, in quarantined labs, which insects most effectively destroy aphids.

Although natural aphid enemies can be found in most soy-growing Asian nations, he chose northeast China because it is similar in climate to Minnesota and is where soybeans originated.

“We try to match climates as much as possible to see which insects are most likely to survive tough Minnesota winters,” Heimpel said.

Minnesota Soybean Research and Promotion Council Chairman Jim Call said the council financially supports University entomology research because it wants to help farmers find a more environmentally friendly and longer-lasting solution.

He said since aphids came to the United States three years ago, they have forced soy farmers in southern and eastern parts of the state to spray almost 100 percent of their crops.

Call said spraying crops also might hurt livestock that eat the soy.

“From an environmental standpoint, (biological controls) are much less harmful than chemicals,” Call said.

Heimpel said because it is a one-time cost, using biological pest controls will be cheaper than insecticide spraying in the long run.

However, University entomology doctoral student Jana Lee said releasing enemy insects is neither a quick nor easy solution. She said she has worked with the same insects for three years and has still not found a solution.

“It doesn’t work as easily as chemicals, but we are still working on understanding which ones will be most effective,” Lee said.

University entomology research assistant Cynthia Hsu said the payoff of biological controls is infinite, but there is a danger of killing other insects along with the aphids.

“We need to collect a lot more background information before we release these bio control agents,” Hsu said. “It doesn’t always work, but when it does, it can be very effective.”

Heimpel said he had some success when he released a Japanese wasp in Minnesota crops last year. The wasps only attacked soy aphids, Heimpel said.

He said he has collaborated with the U.S. Department of Agriculture, Purdue University and the University of Illinois. He said the next step is to find the most promising insect to kill the soy aphids and test them on a larger scale in a U.S. Department of Agriculture quarantined lab.