Innate behaviors shape generalist herbivore host choice and feeding patterns independent of plant defenses

Plant-herbivore interactions are typically examined through plant defense and herbivore performance, yet the behavioral mechanisms underlying these interactions are rarely considered alongside plant traits. We compared two closely related polyphagous chewing herbivores with strikingly different behavioral strategies: One is relatively immobile, attaches tightly to leaves and is more cryptic on foliage, whereas the other is highly mobile, easily detaches from plants, is better camouflaged on soil, preferentially feeds lower leaves, and exhibits reactive anti-predator responses. By quantifying innate herbivore behaviors, plant chemical defenses and morphology, and environmental context, we show that herbivore innate behavior is the primary factor structuring interaction outcomes, even when they carried substantial performance costs in the presence of plant defenses. Further, these behaviors occurred independent of larval stage, across native and introduced populations. Together, our findings show that species-specific behavioral syndromes, rather than plant defense traits, can structure plant-herbivore interactions, with significant implications for coevolutionary trajectories.