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

Soil fertility and resulting crop plant nutrition contribute to optimal crop yields in both conventional and organic farming systems. Additionally, soil management practices can affect the colonization and efficacy of arbuscular mycorrhizae (AM), which in turn may improve crop resilience to drought and soil nutrient deficiencies. Soil mineral fertilization and AM colonization have been shown to affect herbivorous insect oviposition response and performance. However, the below-ground interaction of fertilization practices and AM colonization on plant nutrition and insect oviposition response has been largely unexplored. To test this, we obtained soils from agricultural fields managed under 3 different soil fertilization practices for 5 continuous years: Synthetic fertilizers only with a 2-year corn-soybean rotation (conventional farming, or CONV), dairy manure with a 4-year alfalfa/oat-alfalfa-corn-soybean rotation (standard organic farming, or STDO), and dairy manure + 4-year alfalfa/oat-alfalfa-corn-soybean rotation with biannual gypsum applications (organic basic cation saturation ratio farming, or BCSR). Soils from these treatments have been previously shown to vary significantly in their Ca:Mg:K ratios and also in S content. We reared field corn plants in these soils in a greenhouse, then used them to conduct oviposition choice assays with the corn insect pest Ostrinia nubilalis (European corn borer, or ECB). Colonization of AM on plant roots did not significantly differ among treatments. Plant tissue minerals (primarily S, Fe, and Cu) varied significantly among treatments but were not affected by AM colonization. However, the number of ECB eggs laid per plant per trial varied significantly by soil fertilization treatment, plant height, and AM colonization, with significant interaction effects. Female oviposition response was positively correlated with AM colonization and height in low mineral soil fertilization treatments (STDO and CONV), but moths showed a negative response to AM colonization in BCSR plants as plant height increased. Our results indicate that both fertilization practices and mycorrhizal associations can interact to modify oviposition in pest insects, which may have significant implications for the utilization of fertilization practices for pest insect suppression.