K-State uses geographic tools to track plant pathogens

The Asian soybean aphid — native to China, Korea and Japan — has invaded the United States. It was identified as a distinctly new crop pest on the North American continent in 2000, after appearing simultaneously in 11 states.

Having no natural enemies here to control it, the aphid expanded its range by more than 300 kilometers a year for the next two years, showing up in soybean fields from the Dakotas to Virginia and causing crop losses of more than $2.2 billion.

How did it get here? Probably it was carried in accidentally, says Sonny Ramaswamy, Kansas State University entomology department head. But, in this day and age, scientists have to consider that a new plant pathogen like this could be a deliberate introduction.

He sees the aphid invasion as a training exercise for scientists to prepare for an agroterrorist strike that pits a foreign insect pest against U.S. crops.

“There are interesting commonalities between how insects spread and how pathogens spread,” he said. “In fact, insects, including this aphid, are natural carriers and vectors of a lot of plant pathogens.” The soybean aphid colonizes soybeans, but it carries several viruses that harm other crops like peanuts and alfalfa.

“When I heard about the aphid, I realized we could learn a lot if we studied this outbreak as if it were a deliberate introduction,” Ramaswamy said. On that hunch, he started phoning and visiting K-State colleagues, talking about a project with national security implications.

His collaborators are insect experts, science librarians and modern-day mapmakers. Ramaswamy explained: “We were tackling a complex puzzle: we wanted to see if we could determine how fast the aphid moves, where it’s been; then if we could predict where it’s going throughout the country, and, finally, by looking at the data could we work backwards to determine its point of entry.”

Before 2000, Asia was the only known territory of the soybean aphid. What was known scientifically about natural enemies, host plants, control and management existed in publications in Chinese, Japanese and Korean, but not English.

Enter K-State science librarian Donna Schenck-Hamlin. She directs Information Support Services for Agriculture. She sought funding for a translation project, and with the help of associates in Asia, was able to identify 128 relevant articles that have since been translated into English. They can be read at http://www.ksu.edu/issa/aphids/reporthtml/citations.html

The translation project was expanded to include Korean and Japanese-language publications. K-State’s collaborators are University of Minnesota, Chinese Agricultural University and the Chinese Academy of Agricultural Sciences. Translation funding came from the U.S. Department of Agriculture and the American Soybean Association.

According to K-State science librarian and entomologist Mohan Ramaswamy, the translation effort revealed that China has managed the soybean aphid largely through biological controls, intercropping and traditional plant breeding programs.

K-State Research and Extension Service entomologist John Reese took up the task of creating colonies of Asian soybean aphids for study. The aphid invasion as a proxy for a bioterrorism event is yielding helpful techniques and could lead to an early warning system, he thinks. “Ideally, we’d like to be able to say, ’next growing season, we’ve got a good probability the aphid is going to be seen in specific fields.’”

The Asian soybean aphid reproduces through a combination of asexual and sexual means. Its asexual phase allows it to build to “amazing numbers” during the growing season, Reese said. He noted that, in fact, it’s the only aphid to ever be responsible for cancellation of a sporting event: the players and fans at a Toronto Blue Jays baseball game couldn’t see because of the aphid swarms. “No aphid has ever built up to numbers quite like that,” said Reese.

He contacted K-State geographer and mapping expert Shawn Hutchinson, who directs the Geographic Information Systems Spatial Analysis Lab. So many applications of insect dispersal and movement can be quantified and described in more detail using geographic information system techniques, Reese noted. “Our entomology graduate students routinely take GIS coursework or seek GIS certification. Pairing the two disciplines is a wide-open new field,” he said.

Hutchinson mapped two years of aphid occurrence data for states and counties as recorded on two Web sites: NAPIS and APHID WATCH, a site of the North Central Pest Management Agency.

“GIS has analytical and visualization capabilities that make it a very powerful tool for this kind of research,” he said. An initial finding — the aphid was dispersing more rapidly in an east-west direction.

“Using GIS, we calculated its likely rate of expansion for the 2003 season at 170 kilometers. When the 2003 field-level data became available, our prediction had included all the aphid-positive counties, though not all counties within the predicted expansion zone actually reported aphids in the field,” said Hutchinson. “We are very, very pleased with the prediction model we’ve developed so far.”

Hutchinson is continuing the analysis and has added a geographic database of biological, climatic, and topographic data that uses algorithms created at the San Diego Supercomputing Center. That has yielded a new set of predictions that aphids might be found eventually in the northwest region of the country but probably will not disperse along the Mississippi River valley south of Tennessee.

“In the event of a real agroterrorism event, having a tool like this and expanded geographic databases would be invaluable,” says Hutchinson.

Ramaswamy calls the project “a nice piece of research.” GIS showed how the aphid moved across the country, the topographic and environmental characteristics favoring its dispersal, and where the aphid could go next. But where did it enter the U.S.? Preliminary GIS analysis points to Cook County, Ill., home of Chicago’s O’Hare Airport.

Ramaswamy imagines a grandmother arriving at O’Hare Airport from Asia and being met by her family. Maybe she brought her grandkids some food delicacy like boiled soybeans. The kids gleefully peel and eat the soybeans and toss the shells out the car window on the way home. And maybe, just maybe, one or two female aphids emerged from those shells.

“When you’re talking about insects that reproduce asexually and sexually, one or two females is all you’d need,” he said.

Geographer Nancy Leathers, geography student Jason Herynk and entomologist Leslie Campbell have contributed to this project. The paper, “Agricultural Plant Pathogen Disease Pathways: Predicting the Dispersal of Exotic Soybean Aphids,” appeared in the peer-reviewed Papers of the Applied Geography Conference, November 2003. A second paper is in press with the Annals of the Entomological Society of America.

This research is being conducted through the Plant Pathways Analysis Group of the National Agricultural Biosecurity Consortium, housed at Kansas State University. The U.S. Department of Agriculture Animal and Plant Health Inspection Service, provided funding through the Kansas Agricultural Experiment Station. Other Consortium members are Purdue University and Texas A & M University.