Insect Briefs – Soybean Aphids, Syrphid Flies, and More
Russ Higgins, University of Illinois Extension reports finding a couple of soybean aphids in LaSalle County this week. This follows some earlier reports in July of soybean aphids being found in low numbers in Iowa. Despite some of the recommendations floating around, direct yield loss from soybean aphid feeding does not occur when the first (or five or ten) aphids begin feeding. Today’s soybean varieties are equipped to handle minor challenges, including a few aphids. Yield loss from soybean aphid is related to how many soybean aphids are present and for how long the aphids are present and feeding. The amount of aphid population pressure over time is calculated as aphid-days. Simply put, this is the average number of aphids on a plant multiplied by the number of days they are present. A single soybean aphid on a plant for 10 days is equal to 10 aphid-days, 200 aphids on a plant for 20 days is equal to 4,000 aphid-days, and so on. This aphid-day concept proved to be a good indicator of how soybean yield responded to aphid populations. The lowest level of aphid infestation that has been shown to cause yield loss in soybean is several thousand aphid-days.
*This excerpt was taken from a larger document co-written by many entomologists in the North Central region (see list below). To read the full article with citations, please click on the link: Just the facts: A review of the biology and economics behind soybean aphid insecticide recommendations.
As always, we continue to encourage growers to scout fields and utilize economic established economic thresholds.
University of Minnesota: Bruce Potter, Robert Koch & Phil Glogoza
Iowa State University: Erin Hodgson
Purdue University: Christian Krupke
Penn State University: John Tooker
Michigan State University: Chris DiFonzo
Ohio State University: Andrew Michel & Kelley Tilmon
North Dakota State University: Travis Prochaska & Janet Knodel
University of Nebraska: Robert Wright & Thomas E. Hunt
University of Wisconsin: Bryan Jensen
University of Illinois: Kelly Estes & Joseph Spencer
– I’ve received a few reports of maggots in corn. I believe these insects are syrphid fly larvae. One report indicated large numbers of these larvae throughout the entire corn field. Syrphid fly larvae are actually predators of soft-bodied insects like aphids. They are not causing injury to the corn. Perhaps some of you may remember a similar story out of Indiana last year: https://www.no-tillfarmer.com/articles/4935-looping-worms-and-sweat-bees-seen-in-corn
– Despite inconsistent moth flights, there are reports of fall armyworm and corn earworm feeding in corn.
– We’ve had a few western bean cutworm in traps in northern Illinois. Flights generally peak in mid-July.