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Corn Defense Responses to Nitrogen Availability and Subsequent Performance and Feeding Preferences of Beet Armyworm (Lepidoptera: Noctuidae)

Ren, Li-Li, Hardy, Giles, Liu, Zhu-Dong, Wei, Wei, Dai, Hua-Guo
Journal of economic entomology 2013 v.106 no.3 pp. 1240-1249
Spodoptera exigua, Zea mays, carbohydrates, corn, energy, feeding preferences, fertilizer application, larvae, nitrogen, nitrogen content, nitrogen fertilizers, nutritive value, phenolic compounds, phytophagous insects, plant growth, plant-insect relations, population dynamics
Many studies have reported the effect of nitrogen (N) fertilization on plant constitutive defense responses; however, little is known about their effects on plant induced defense patterns and its consequence for insect herbivores. In our experiments, the effects of N availability on growth, nutritional quality (N content, protein/carbohydrate [P:C] ratio, modified gross energy [MGE]), and constitutive phenolics of corn, Zea mays L. were quantified. Moreover, the indirect effects of N fertilization on the beet armyworm, Spodoptera exigua Hübner through larval performance and feeding preference were examined. N fertilization increased plant growth, and depressed defense traits by increasing N content and the P:C ratio, as well as decreasing the constitutive concentration of phenolics. Subsequently, beet armyworm showed higher performance and preferentially fed on high-N corn because of its low defense traits. After beet armyworm feeding, high-N corn significantly deterred larval feeding, and had negative effects on the performance of beet armyworm through decreasing P:C ratio and increasing induced phenolics. On the contrary, there were no significant changes in P:C ratio and phenolics in low-N corn after feeding damage. Larval performance and preference were also not affected by induced compounds in low-N corn, which suggested that the expression of induced defense was dependent on N availability. The result indicates that N availability can exert a variety of bottom-up effect on plant defense patterns to influence insect population dynamics, and thereby may represent a source of variation in plant-insect interactions.