Influence of Crop Variety and Fertilization on Oviposition Preference and Larval Performance of a Generalist Herbivore, the True Armyworm, Mythimna Unipuncta

The relationship between oviposition preference and offspring performance of herbivores is an essential question in the field of plant–insect interactions and may have important implications on integrated pest management practices. Here, we investigated the preference–performance relationship of a generalist herbivore, the true armyworm, Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae, Leucaniini). We evaluated the effect of crop species, cultivars, and fertilization rate on host use by adult and larval M. unipuncta in both laboratory and field experiments. Female M. unipuncta preferred to oviposit on cereals (Triticum aestivum L., Hordeum vulgare L., Zea mays L., all Poaceae) compared to oilseed (Brassica napus L., Brassicaceae) or pulse (Pisum sativum L., Fabaceae) crops. The preference–performance relationship was examined further on four cereal crops, spring wheat (T. aestivum cv. CDC Go), winter wheat (T. aestivum cv. CDC Buteo), feed barley (H. vulgare cv. Xena), and malt barley (H. vulgare cv. Copeland). Feed barley was the least preferred cereal by female moths but resulted in the highest larval performance of all tested plants suggesting that females did not select the host on which their offspring performs best, based on nutrient content. In contrast, late‐instar larvae selected the hosts, feed barley and malt barley, on which they performed the best, suggesting that larvae have a more active role in host selection for development, compared to adult females. The addition of fertilizer to host plants did not influence adult female oviposition preference. Larvae reared on plants treated with the half (70 mg N) or full (140 mg N) dose of fertilizer resulted in heavier pupae, compared to those reared on unfertilized plants, regardless of crop variety. However, under field conditions fertilization did not enhance larval performance on feed barley plants. The generalist herbivore M. unipuncta does not exhibit the ‘mother knows best’ principle on the tested hosts and potentially employs a bet‐hedging strategy instead.