Sweet maize hybrids' yield response to adult western corn rootworm (Diabrotica v. virgifera Leconte, Col.: Chrysomelidae) silk feeding and IPM implications thereof

The western corn rootworm [Diabrotica virgifera virgifera LeConte (WCR)] is an important pest of maize in USA and Canada, and Europe. Its primary damage is due to larvae feeding on maize roots; yield and quality also occur due to WCR adult silk clipping and interference with ear pollination. WCR economic thresholds for sweet maize hybrids are not available. We aimed to determine whether silk feeding and artificial silk cut in various sweet maize hybrids could be correlated to potential WCR adult levels. The two-year field study was conducted in Hungary using seven different sweet maize hybrids. The silk was cut back to 0, 1, and 2 cm, measured, and compared daily to the silk length of uncut control plants. As a separate treatment, WCR adults were placed in cages on the uncut Suregold hybrid to assess silk clipping activity. After harvest, cob weights were measured, and fertility levels were assessed. Results showed that sweet maize hybrids can tolerate some silk cutting (simulating high WCR density and silk feeding). The action threshold for these hybrids is much higher than that for inbred lines or commercial grain maize, in line with prior studies for the Suregold hybrid (8-12 adults per year). Meteorological conditions and multiple pest presence, phytosanitary regulations, and IPM considerations may help finetune adult WCR control intervention decisions.