The effect of zinc fertilizer on maize growth, leaf mineral nutrition, and caterpillar herbivory

Mineral nutrients, such as zinc (Zn), are critical for plant growth; however, the effect of Zn on insect herbivory is poorly characterized. Because Zn deficiency may compromise plant physiology while high levels of zinc may be directly toxic to herbivores, we predicted lepidopteran herbivores would perform best on plants deficient in Zn or those with an intermediate dose of Zn fertilizer. We first tested these hypotheses in a greenhouse experiment using maize (Zea mays L. [Poaceae]) and two noctuid caterpillars, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) and Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and evaluated the effects of a normal range of Zn (0–11.7 g m⁻³) on the interaction between maize and each caterpillar species. In the greenhouse, we found Zn increased uptake of other nutrients, particularly nitrogen (N), and fertilizing with just 2.5 g m⁻³ Zn maximized maize growth. Spodoptera frugiperda performance increased marginally with Zn fertilization. While neither caterpillar species was directly affected by Zn concentrations in leaves, S. frugiperda caterpillars responded to leaf N. In the field, we investigated the effect of Zn fertilization on leaf-nutrient concentrations, early season damage by resident herbivores, performance of S. frugiperda on excised leaf tissue, and maize yield. We found fertilizing with Zn increased leaf N, but compared to the greenhouse experiment, had a smaller effect on Zn uptake and no effect on herbivory. Zinc treatments did not affect maize yield in the field. We conclude that Zn fertilization can increase N leaf concentrations, which in turn can affect some herbivores, with species-specific effects.