AMES, Iowa--For Iowa soybean farmers, aphids are rapidly becoming enemy number one. Their numbers for this year's growing season topped the charts. Left unchecked, soybean aphids can cut yields by as much as 40 percent.
And now aphids aren't just for soybeans anymore. Iowa's aphid diversity is on the rise and the population now includes "aphid species that feed on cereal crops as well as perennial grasses that may be used for biofuels," said Allen Miller, director of the Iowa State University Plant Sciences Institute's Center for Plant Responses to Environmental Stresses and professor of plant pathology.
Miller and Institute affiliate Bryony Bonning, a professor in the department of entomology, are capitalizing on this year's bumper aphid crop by collecting aphids to search for viruses that specifically infect soybean aphids. If successful, they will be the first to identify a soybean aphid virus.
Their efforts are a step in the process toward creating a biopesticide to control Iowa's soybean aphid population, which arrived in the Midwest several years ago from Asia. These biopesticides could help eliminate the use of crop dusting with pesticides, which kill indiscriminately.
Bonning and Miller are working at the molecular level with natural aphid viruses, tailoring them to kill only targeted aphid species. The researchers' most recent results appear in the September issue of the Journal of Virology.
To understand the viral biology, or how these viruses infect the insect and what they do once inside the aphid's cells, Bonning and Miller needed to clone an aphid virus.
They chose the Rhopalosiphum padi virus, named for the Latin name of its favorite host, the bird cherry-oat aphid, a widespread and abundant aphid that feeds on cereals such as maize, barley, oats and wheat.
The biggest challenge in the lab for Bonning and Miller was to find a cultured cell line in which the virus could reproduce, because to date, no one has been able to grow aphid cells in culture. A cell line from an insect called the glassy winged sharpshooter--a major grapevine pest-worked.
"This is the first time anyone has successfully reproduced a virus from this family of viruses and one that is able to infect its natural host--in this case, aphids," said Bonning.
The advent of Bonning and Miller's viral clone means the researchers can begin the work of understanding how the virus infects and damages its host. It also opens up the possibility for genetically engineering or manipulating the virus to work as a biopesticide.
Coincidentally, Bonning and Miller's aphid pest management research efforts have crossed paths with others concerned with the rescue of honey bees from the recently observed Colony Collapse Disorder.
The collapse of honey bee colonies all over the United States has caused much alarm among bee keepers and farmers because honey bees are the sole pollinators of many crops and partially responsible for the pollination of many others. Bee pollination of fruits, vegetables and nuts alone is worth billions of dollars to U.S. agriculture.
A recent report has linked collapsing honey bee colonies with infection by a virus from the same family as Bonning and Miller's cloned aphid virus. This report recently appeared in the online supplement to the journal Science (www.sciencemag.org/cgi/content/abstract/1146498).
As for the aphid, there is no existing cultured bee cell line.
"But we've set a precedent about how they can produce their virus in vitro in the absence of a bee cell line to study its biology and possibly find a way to render it benign," said Bonning.
"Our project was technically challenging, and really high risk," said Bonning. "But in addition to our own goals, we came out with a state of the art methodology that the bee researchers can use."