Source: AgAnswers, an Ohio State Extension and Purdue Extension Partnership

The soybean aphid, an insect pest whose quirky behavior has made it more famous than the actual damage it causes, is doing something this season that Midwest entomologists might have successfully predicted: absolutely nothing.

The insect, which can level soybean fields with its voracious appetite if populations are high enough, is missing in action so far this season - and not only in Ohio, but also throughout the Midwest.

"It's very difficult to find the soybean aphid in Ohio. Most people who go out looking for it probably won't find it," said Ron Hammond, an Ohio State University research entomologist. "Not only is nothing happening in Ohio, but nothing much is happening in the Midwest. Reports from northern states indicate researchers aren't finding many of the insects up there. For example, in Minnesota, only six fields were identified last week with the aphid. This time last year, the state was spraying hundreds of fields."

Researchers are patting themselves on the back for what is turning out to be an accurate prediction of soybean aphid populations this season. If the prediction holds true, aphid populations could be falling into a cycle of low one year and high the next.

"Last year, the soybean aphid was just awful, with high populations throughout the Midwest," Hammond said. "If populations stay low this year, we expect insects to overwinter this fall and explode next year in high numbers."

When the insect was discovered in the Corn Belt in 2001, masses of winged aphids sent people running for cover as far north as Canada. The following year, aphid populations were uncharacteristically low. Populations rose again in 2003.

Researchers believe aphid populations may be tied to the population of the multicolored Asian ladybeetle, a known predator. Put simply, when soybean aphid numbers are high, ladybeetle numbers also are high.

Although controlling aphids during summer months is light, the ladybeetles may prevent the aphids from overwintering by actively feeding on them in the fall. Ladybeetle populations are expected to be low this year because aphid numbers also are low, which would account for researchers' assumptions that aphid populations will be high next season.

"We expect to see some aphid population build up at the end of this summer, but how much we don't know yet," Hammond said. "But just because soybean aphid populations are low right now doesn't mean growers should be forgetting about the insect. They need to be out in their fields scouting for the insect, as usual. We will know that our prediction of low aphid populations is accurate only at the end of the season. Time will tell."

That's good advice to follow now that other insects are emerging, and at a time when soybean plants are most sensitive to insect defoliation. Bean leaf beetles, Mexican bean beetles, Japanese beetles and grasshoppers are likely to be making an appearance soon, if they aren't already emerging.

"Insect defoliation is an issue growers face every summer, and all we can do is recommend to growers to pay attention to any defoliation and take action, if necessary," Hammond said. "It's normally not one insect that will cause significant damage, but when you add up all these insects, then you can start reaching thresholds."

Hammond recommends growers pay special attention to the bean leaf beetle, whose first-generation brood feeds on plants and second generation can feed on pods.

"Use first-generation populations as an indication of how high the second generation will be," Hammond said. "If first-generation populations are high, then second-generation populations, which emerge in August and September, might also be high."

Hammond also recommends a technique to help reduce the additional spread of bean pod mottle virus, which is based on Iowa State University research.

"For those growers who sprayed to control the overwinter populations to lower the transmission of bean pod mottle virus, research has shown that another treatment targeted at the first generation helps to slow the feeding of bean leaf beetles and, hence, slows the continued spread of the virus," Hammond said.