PEORIA, Ill. – Grape colaspis and corn leaf aphid outbreaks in parts of Illinois were among the top crop pests of the 2025 growing season, causing plant injury and, in some cases, loss of yield production. The good news: because the insects, especially colaspis, are sporadic in Illinois, history suggests that issues in 2025 do not necessarily translate to another big year for the pests in 2026.

This is according to Dr. Nick Seiter, assistant professor and field crop entomologist for the University of Illinois Extension, who noted that a significant outbreak of colaspis, which resemble bean leaf beetles in size and shape but have stripes along the back, had not been seen in Illinois since 2018. Speaking to a group at the Greater Peoria Farm Show in December, Seiter explained that grub-like grape colaspis is most commonly found in elevated areas of crop fields, and can be found in corn-after-soybean or even soybean-after-soybean rotations.

‘We often see (colaspis) in corn grown in rotation with soybeans or another legume. They feed on the root hair system as it is developing, and they do so in such a way that interferes with nutrient uptake,” said Seiter, adding that for this reason farmers may initially confuse the damage incurred from colaspis with symptoms of a nutrient deficiency.

“Particularly with phosphorus and potassium, where you get the purpling and yellowing of the leaves. That’s kind of the first indication you have a problem, where they shouldn’t really be showing up based on the fertility profile of that field,” he added. 

Seiter last reported on grape colaspis in an April 2019 paper, “Grape Colaspis in Corn and Soybean: a Pre-Season Primer.” (Department of Crop Sciences, University of Illinois at Urbana-Champaign). He noted that colaspis larvae, which feed below ground and resemble tiny white grubs, are responsible for plant injury. Plants may appear wilted, stunted, or as if they have a nutrient deficiency from above the soil surface. The damage is often patchy and most pronounced on high or well-drained portions of a field. Uprooting damaged plants will reveal the larvae, which resemble white grubs, though smaller.

While plants will usually overcome initial larvae damage, severe feeding can kill plants and reduce stands. Because egg laying occurs in soybean, alfalfa and other legumes, the damage can occur in rotated corn or continuous soybean.

“The severity of damage can be spotty; it can kill or stunt a plant. Usually where we see this in fields are the higher, better-drained portions of a field and (the damage) can sometimes result in a partial re-plant. Very infrequently would you see colaspis wreck an entire field,” Seiter said, adding that the most colaspis-infected field he ever “walked” was in the Blue Mound-Mt. Auburn area of south central Illinois last summer. “It was still spotty in that field, but the spots that were affected probably took up around half the field itself. It was a pretty serious situation with some stand loss.”

The geography in Illinois regarding grape colaspis seems to be restricted thus far to a “belt” across south-central Illinois from around Springfield toward Terre Haute, Ind., according to Seiter. The bug expert also assured the Peoria farmers that just because grape colaspis made a return in 2025, there is no particular reason to think pressure from the pest will return or increase in 2026. “It’s very sporadic, and we will kind of see ‘outbreak years’ when we have the right combination of environmental conditions, but it happens infrequently enough it’s kind of hard to even determine what those conditions are,” he said. “2018 was the first time it had been seen in (large numbers) for 10 or 12 years prior, though we see some of the beetles every year. If you walk bean fields you see it is never completely gone.”

Seiter said Illinois farmers also saw a continuance of pressure from corn leaf aphid on certain hybrids in 2025, though the insects’ numbers were not as great as in 2024. “In 2024 we had a rather large outbreak, even causing some yield loss in fields, which is something we really don’t see very often with that insect,” he said. 

“In 2024 we were seeing differences from hybrid to hybrid and variety to variety. Though in 2025 we did not see widespread outbreaks of the insect, we got reports that some of those hybrids that were sensitive in 2024 were sensitive again in 2025 to that aphid.”

Still, with proper hybrid management and selection farmers should not expect to see increased pressure from corn leaf aphid in 2026, according to the entomologist. “Corn leaf aphid is even more sporadic than grape colaspis,” said Seiter, who can be reached with questions at nseiter@illinois.edu.