Oviposition site selection on oats: The effect of plant architecture, plant and leaf age, tissue toughness, and hardness on cereal leaf beetle, Oulema melanopus

In sequentially planted oat stands, the cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae: Lemini), is found in greater numbers, and lays more eggs, on later planted (younger) oats (Avena sativa L.) (Poaceae). Plant characteristics that could explain this ovipositional preference were examined in a series of experiments. Cage and open field whole plant preference tests confirmed the attraction of ovipositing females to younger oats. A cage effect illustrated the role of plant architecture (plant height) in CLB host selection. Two multiple-choice and one no-choice excised leaf experiments determined that characteristics of individual leaves associated with leaf insertion level (leaf number from base to apex) and age influence ovipositional site selection. Leaves of higher insertion level have higher nitrogen content, but fewer eggs are laid on those leaves. Two experiments examining the interaction between total leaf nitrogen and leaf insertion level showed that only leaf insertion level affected oviposition choice. Published literature suggests variation in secondary plant compounds cannot explain O. melanopus ovipositional preference among leaves. Grass leaves of higher insertion level have more extensively developed cells associated with tissue toughness and hardness. The data and supporting literature suggest tissue toughness and hardness are deterring oviposition on oat leaves of higher insertion level. However, newly eclosed larvae are able to feed on leaves usually avoided as oviposition sites. The explanation for this result may be a lack of correlation between host suitability and ovipositional preference.