Soil-Management History and the Role of Plant Mineral Balance as a Determinant of Maize Susceptibility to the European Corn Borer

Abstract

Proponents of organic fanning 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: (I) maize plants with an optimal mineral balance show lower susceptibility to insect pests, (2) detennining 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.

Reduced Fitness of the Colorado Potato Beetle (Coleoptera: Chrysomelidae) on Potato Plants Grown in Manure-amended Soil

“…The differences could not have been attributed to the reduction in plant vigor in the absence of chemical fertilizers because we did not detect any difference in plant size or canopy cover, while yields were actually higher in manure-amended plots. Because natural enemy pressure on Colorado potato beetle populations in northern Maine is extremely limited, Alyokhin et al 2005 speculated that, in accordance with the mineral balance hypothesis (Phelan et al 1996, Phelan 1997, the observed response was plant-mediated. However, before this study, no direct evidence was available to show that growing on manure-amended soils indeed makes potato plants less suitable Colorado potato beetle hosts.…”

“…Plants grown on organically managed soils fertilized with manure and compost have been shown to be less favorable hosts for phytophagous insects than plants grown on conventionally managed soils fertilized with synthetic fertilizers (Eigenbrode and Pimentel 1988, Phelan et al 1995, 1996. Phelan et al (1996) and Phelan (1997) suggested a hypothesis that the organic matter and microbial activity associated with organically managed soils afford a buffering capability to maintain nutrient balance in plants. An optimal nutrient balance results in both good plant growth and resistance to herbivory, while crops growing in soils without these biologically based buffering capabilities are more likely to take up either excess or insufÞcient levels of certain nutrients.…”

Micronutrient Interactions on Soybean Growth and the Developmental Performance of Three Insect Herbivores

“…In an attempt to explain differences in pest pressure between organic and conventional systems, Phelan et al (1996) and Phelan (1997) offered the "mineral balance hypothesis," which postulates that the organic matter and microbes associated with organically managed soils afford a buffering capability to maintain nutrient balance in plants. It is further suggested that an optimal nutrient balance results in both good plant growth and resistance to herbivory.…”

European corn borer oviposition response to soil fertilization practices and arbuscular mycorrhizal colonization of corn

“…Though ECBs preferentially oviposit on corn, they also respond to volatiles of, and will readily oviposit on, other plant species (Udayagiri and Mason 1995), which suggests that ECBs are responding to chemical conditions within their host plants that are not plant speciesspecific. Studies with corn plants have shown that not only does O. nubilalis oviposition rate change significantly in response to different fertilization practices (Phelan et al 1995), but also to mineral profiles within individual plants (Phelan et al 1996, Phelan 1997. This broad response to chemical composition of host plants makes O. nubilalis a good model organism, as well as an economically important one, in which to assess fertilization-mycorrhiza mediated oviposition response.…”

“…Some herbivorous insect species have been shown to lay fewer eggs upon, or show reduced performance when feeding upon, crops grown with organic fertilizers as opposed to synthetic fertilizers (Phelan et al 1995, Morales et al 2001, Hsu et al 2009, Cardoza 2011. Also, plants that have been reared in organically managed soils can achieve a ratio of microminerals (Mg, Ca, Fe, Al, Mn, Cu, Zn) that may make them less susceptible to herbivorous insects (Phelan 1997).…”