The European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Crambidae), is one of the most economically important pests of agricultural crops in much of the eastern and central United States. O. nubilalis is particularly damaging to sweet peppers (Capsicum annuum L.) because it causes direct injury to the fruit, premature fruit ripening, and fruit rot, a result of pathogens such as Erwinia carotovora entering the feeding wound.
Effective control of O. nubilalis in peppers is only achieved by multiple preventative insecticide applications, often with little or no knowledge of the pest density in the field. Sampling for O. nubilalis could reduce the number of insecticide applications as part of an overall Integrated Pest Management (IPM) program. However, quantifying O. nubilalis larvae in the plant canopy can be difficult due to their small size and propensity to quickly bore into plant tissue (Fig. 1), often the fruit, where they are protected from chemical sprays.
The monitoring of egg masses may be a better way to quantify O. nubilalis for developing an IPM scouting program. As a result, we attempted to identify likely areas of O. nubilalis egg masses within the plant canopy allowing more accurate estimation of O. nubilalis population numbers in the field. We collected a total of 362 O. nubilalis egg masses on pepper plants during our study. The results were that only three egg masses (0.8%) were found on plant structures other than a leaf, including one on a stem and two on fruit. Over 93% of egg masses were found on the lower surface of the leaf compared with the upper surface indicating a significant egg laying preference for the undersides of leaves (Fig. 2). This may be a strategy to reduce egg mortality from fluctuating environmental conditions as well as predation by natural enemies. No differences were found in the observed distribution of egg vertically throughout the plant (Fig. 3). This suggests that O. nubilalis does not have a vertical preference for oviposition in the canopy of a bell pepper plant which is similar to findings in sweet corn that showed a uniform vertical distribution of O. nubilalis egg masses on plants. Possibly the uniform egg mass deposition within the plant canopy is a strategy to minimize intraspecific competition by O. nubilalis for food resources.
In summary, we conclude that O. nubilalis females primarily (>93% of the time) oviposit on the undersides of leaves on pepper plants, but with no apparent preference for vertical region on the plant. An egg sampling strategy for O. nubilalis in peppers should concentrate on the underside of leaves on all regions of the plant.
Originally printed in Virginia Vegetable, Small Fruit and Specialty Crops – July-August 2004.
Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
July 30, 2009