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

1. Plant-herbivore interactions are typically examined through plant defense and herbivore performance, yet individual herbivore behavioral mechanisms underlying these interactions are rarely considered alongside plant traits.2. We characterized key behavioral differences between the two closely related polyphagous lepidopteran chewing herbivores, Spodoptera exigua and S. littoralis, and quantified the contribution of herbivore traits, plant chemistry, and environmental factors to these behaviors and their consequences for plant and herbivore performance.3. The two herbivore species exhibited strikingly different behavioral strategies: S. exigua is relatively immobile, attaches tightly to leaves and is more cryptic on foliage. In contrast, S. littoralis is highly mobile, easily detaches from plants, is better camouflaged on soil, preferentially feeds on lower leaves, and exhibits reactive anti-predator responses.4. By quantifying herbivore behaviors, plant chemical defenses and morphology within an environmental context, we show that innate herbivore behavior is the primary factor structuring interaction outcomes for both species, even though they carry performance costs in the presence of plant defenses. Further, these behaviors occur independent of larval stage, across native and introduced populations.5. Together, our findings show that species-specific behavioral syndromes, rather than plant defense traits, can structure plant-herbivore interactions. This can have important implications for plant-herbivore coevolutionary trajectories, if plant defense capacity does not limit herbivory and herbivore behavior is not modified by plant defense status.