By Yucheng Wang and Tatum Dwyer et.al
During July-August 2025, we unexpectedly observed significant damage resembling European corn borer (ECB) injury along the edges of several corn fields in Martin and Mower Counties, Minnesota (Figure 1).
Affected plants showed rows of holes on the leaves and boring damage in the stalks. However, dissection of the corn stalk revealed that the culprit was common stalk borer (CSB), Papaipema nebris (Guenée) (Lepidoptera: Noctuidae), rather than ECB (Figure 2).
Bt trait testing of the affected plants confirmed the expression of several Bt proteins, including Cry1F, Cry2A, Cry3Bb, and Cry34/35 (Figure 3). Among these, Cry1F and Cry2A target lepidopteran insects and are expected to suppress CSB infestations, whereas Cry3Bb, and Cry34/35 are only effective against corn rootworms.
Damage was concentrated in the first few rows next to grassy areas, while interior rows remained largely undamaged. In one field, approximately 60-70% of the plants along the first few rows, based on ~200 sampled plants, showed visible injury near the ditch. This edge pattern of injury is characteristic of the common stalk borer’s migration behavior from grassy weeds into corn early in the growing season. Further investigation is needed to determine whether the survival of CSB larvae in these Bt corn plants is resulting from the movement of large larvae or potential resistance to Bt proteins.
Source : umn.edu