Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2009
Publication Date: 4/1/2009
Citation: Lewis, L.C., Bruck, D.J., Sumerford, D.V., Gunnarson, R.D. 2009. Technique to Assess Effectiveness of Control Tactics Against Ostrinia nubilalis (Lepidoptera: Crambidae) in Whorl-stage Corn. Journal of Economic Entomology. 102(2):624-628. Interpretive Summary: The European corn borer (ECB) is a primary pest of corn in the Midwest, damaging corn both in the whorl stage, when leaves are still unfurling, and the pollen-shedding stage. Both generations of the ECB finish their life cycle by boring into the plant and making tunnels in the stalk. Entomologists evaluate plant protection products by placing laboratory-produced insects in the whorl of small corn plants. Once the larvae have had time to tunnel within the plant, the plants are split from tassel to the base and the cm of tunnels made by the insect recorded. Stalk splitting is labor intensive and one must wait at least 40 days post application to determine efficacy of a product. Research was conducted where laboratory-reared ECB were placed in the whorl of plants, toxicant applied, and the whorls of the plants were pulled at several intervals later and the number of live larvae counted. Then, 40 days post application, the plants were split and tunneling recorded. The numbers of live larvae in the whorl were indicative of the amount of tunneling. The method of whorl pulling and counting of larvae will make evaluation of plant protectant products less labor intensive and the process can occur much sooner in the growing season. This information is useful to IPM practitioners and research entomologists.
Technical Abstract: The European corn borer, Ostrinia nubilalis, is one of the most damaging insect pests of corn. Studies were conducted to determine if live larval counts obtained from corn whorls were indicative of the amount of larval tunneling that would result at the end of first generation O. nubilalis feeding. Whorls from plants treated with Dipel® 10G [6400 International Units (IU) per whorl] and untreated controls, both infested with O. nubilalis neonates, were evaluated for the number of live larvae recorded 5, 7, 9, 11, and 18 days following Bacillus thuringiensis application. Forty days following larval infestation, 25 plants from each plot were split from tassel to base and the cm of larval tunneling recorded. Experiments were performed at multiple locations in 1990, 2000, and 2002. B. thuringiensis significantly reduced the number of live larvae and cm of larval tunneling. Live larval counts from the whorl of vegetative corn were indicative of the amount of tunneling injury that resulted and is a practical method to access the efficacy of control measures implemented against first generation O. nubilalis injury. There was a significant effect of location on the amount of damage that would occur. Qualitative relationships between the number of insects in the whorl and subsequent injury to the plant were apparent at all locations. However, additional data sets specific for each location are required to develop predictive, quantitative relationships between the number of insects in the whorl and subsequent injury to the plant.