Colorado potato beetle response to soil amendments: A case in support of the mineral balance hypothesis?

The mineral balance hypothesis [Phelan, L.P., Norris, K.H., Mason, J.F., 1996. Soil management history and host preference by Ostrinia nubilalis: evidence for plant mineral balance mediating insect-plant interactions. Environ. Entomol. 25, 1329-1336] suggests 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, in turn, results in both good plant growth and resistance to herbivory. Effects of soil amendment practices on Colorado potato beetle populations in potato fields and their interactions with crop rotation and two pest management approaches were investigated in the present study. Beetle densities were generally lower in plots receiving manure soil amendments in combination with reduced amounts of synthetic fertilizers compared to plots receiving full rates of synthetic fertilizers, but no manure. Crop rotation and pest management approaches had little or no effect. Unlike beetle abundance, plant height and canopy cover were comparable between plots receiving manure and synthetic fertilizer. Furthermore, tuber yields were higher in manure-amended plots. In direct accordance with the mineral balance hypothesis, there was a dramatic dissimilarity in mineral composition of potato leaves collected from manure-amended and synthetic fertilizer-treated plots. Overall, there were differences in concentrations of nitrogen, calcium, magnesium, phosphorus, aluminum, boron, copper, iron, manganese, and zinc. Boron concentration was most dramatically affected by the soil amendment. Mineral content of potato leaves explained 40-57% of the variation in the Colorado potato beetle populations observed among the experimental plots. (c) 2005 Elsevier B.V. All rights reserved.