Soil-management history and host preference by Ostrinia nubilalis: evidence for plant mineral balance mediating insect-plant interactions

Organic-farming practitioners have long suggested that maximizing soil biotic activity results in crops of reduced susceptibility to pests. In the current study, we examined the ovipositional preference of Ostrinia nubilalis (Hubner), the European corn borer, on sweet corn grown in the greenhouse using soils from neighboring organic and conventional farms and fertilized with NH4NO3, cow-manure compost, or left unamended. In addition to ovipositional preference, we compared photosynthetic potential, leaf-mineral profiles, and biochemical profiles measured by near-infrared (NIR) spectroscopy. Significant variation in O. nubilalis oviposition among fertilizer treatments was measured for plants in conventional soil, but not for those in organic soil. Photosynthetic parameters, notably net photosynthesis and stomatal conductance, correlated strongly with plant biomass accumulation, but no correlations with O. nubilalis preference were detected. In contrast, a quadratic model of 3 leaf-mineral levels (Zn, Al, and N) showed a strong relationship with O. nubilalis oviposition (adjusted r2 = 0.71); plant growth was best described by a quadratic model of N alone (adjusted r2 = 0.69). The greatest differences in NIR spectra were caused by protein, and soil-fertilizer combinations producing the lowest protein levels were those whose plants received the greatest number of O. nubilalis eggs. We suggest that differences in corn acceptability to O. nubilalis is at least in part mediated by plant mineral balance, which incorporates both absolute levels and ratios of minerals, and that an optimal balance of these minerals is more likely to occur in organically managed soil because of an inherent property of reducing variation in mineral availability in those soils