First the good news – soybean aphids are getting munched on by parasitic wasps.
Now the bad news – soybean aphids may be spreading disease in potatoes.
Potatoes are not a suitable food source for soybean aphids, but aphids land in potato fields, probe the plants and spread disease.
Hopefully, the natural predators of soybean aphids can win out and keep aphids under control in soybeans and potatoes.
For over a decade, soybean aphids have invaded soybean fields in the upper Midwest. Soybean aphid outbreaks continue, but scientists and farmers have noted that populations seem more moderate in some locations.
Aphid reductions could be a result of dry conditions, but could also be a result of natural predators.
“Populations in northern China, the aphid’s home range, rarely rise to outbreak levels,” said Ian MacRae, University of Minnesota Extension entomologist, Crookston.
MacRae spoke to farmers during the Minnesota Soybean Research & Promotion Council See For Yourself Minnesota Road Trip.
His research interests include site-specific integrated pest management. When asked by farmers about soybean aphids, he shared some of the research conducted at the University of Minnesota by George Heimpel, University of Minnesota entomologist, and others.
A parasitic wasp called Alphelinus certus, which is about the size of a gnat, is eating aphids from the inside out. The wasp will lay an egg in the aphid’s abdomen. The hatchling then uses the aphid as a food source.
MacRae said farmers could learn to identify parasitized aphids.
“Occasionally, you will look at aphids and they are a great neon green and feeding happily,” he said. “Sometimes the aphid will look brown and crusty and even have a hole in its back. One of these parasitic wasps has gone through a whole life cycle in there.”
He pointed out that at 250 aphids per plant on 80 percent of the plants, natural mortality can’t keep up with aphid reproduction.
“When that happens, boy, we really need to step in,” he said. “It gets back to the 250 aphids per plant on 80 percent of the plants.”
Researchers and farmers are hoping natural pests – like A. certus – can control soybean aphids before outbreaks occur, and also help prevent disease in potatoes.
In recent years, seed potato growers have seen an increase in Potato Virus Y (PVY) – a plant pathogenic virus that affects potato production. PVY can also affect tomatoes, green peppers, petunias and weeds.
PVY is spread by many species of aphids.
The sucking insect uses its stylet to probe a sick plant. Virus particles attach to the stylet, and when the aphid probes the next plant, the virus particles on the stylet are transferred.
MacRae said the acquisition and transmission of a non-persistent virus like PVY takes only seconds.
“Soybean aphids are restricted to soybeans as a summer food source and buckthorn in the fall and spring. They do land in potato fields and will probe potatoes to assess if they are suitable food sources – (they aren’t). When they find they’re not a suitable food source, they’ll fly off to another plant to assess that one,” said MacRae. “That’s how they transmit non-persistent virus like PVY.
“They may sample a number of plants in the field, but won’t stay on potato plants or leave daughters.”
MacRae said the most effective vector of PVY is the green peach aphid – but there are years when scientists find high PVY levels but low populations of green peach aphids.
Scientists are using suction traps to monitor aphids in seed potato growing regions, and they are finding soybean aphids in the traps.
MacRae said there are a number of researchers now trying to observe the movement of soybean aphids from soybean fields to potato fields.
He encourages farmers who are interested in PVY to visit www.potatovirus.com to learn more.
Scientists also continue to observe the natural predators of soybean aphids. They are hopeful that parasitic wasp populations can keep aphid populations under control.
“We rarely see soybean aphid populations of 12,000 per plant anymore – even in Fergus Falls and Underwood,” said MacRae. “The populations are lower in many areas – so it’s good news.
“Hopefully we are looking at increased natural mortality, and we’ll find this pest easier to control.”