Entomologrcul Reseurch in Orgunrc Agriculture, pp 25-34 O 1997 A B Academic Publ~shers Pnnted In Great Britain Soil-Management History and the Role of Plant Mineral Balance as a Determinant of Maize Susceptibility to the European Corn Borer '.. "b -, P.L. Phelan Department of Entomology, The Ohio Agrlculturai Research and Deveiopment Center, The Ohio State University, Wooster, OH 44691, U.S.A. ABSTRACT Proponents of organic farming have long suggested that their methods produce "healthy" crops that are less susceptible to insects and diseases. Experimental comparisons of European corn borer (ECB) egg-laying response to maize plants grown in a greenhouse in soil collected from either organically or conventionally managed farms provided evidence consistent with these assertions. In each of three paired comparisons, higher egg-laying occurred on plants in conventional soil. Subsequent studies suggested that differences in ECB ovipositional preference were related to plant-mineral balance; a three-mineral quadratic model showed strong predictive power for ECB oviposition. A role for plant minerals was also suggested in a study of paired maize fields with high and low ECB populations compared at three different geographic locations. Significant differences in leaf-mineral profiles between fields were measured that were consistent across locations. Based on these cumulative findings, it is hypothesized that: (1) maize plants with an optimal mineral balance show lower susceptibility to insect pests, (2) determining the effects of minerals on susceptibility must include consideration of both ratios and absolute levels, and (3) a more resistant physiological state is more likely in organically managed soils because of the inherent greater capacity of these soils to buffer availability of minerals to plants. INTRODUCTION One of the cornerstones of organic farming is the assertion that such management systems produce crops that are more resistant to pests and diseases (Howard, 1940; Oelhaf 1978; Geisler 1988; Luna 1988). The colloquial explanation for this claim is that "healthy soil produces healthy plants and pests do not feed on healthy plants ". Although the idea has a long history, there have been surprisingly few attempts either to examine this phenomenon empirically