Differences in 1,4-benzoxazin-3-one profile and induction during growth of young maize affect foraging patterns of leaf herbivores

Abstract: 1,4-benzoxazin-3-ones (BXs) are the major secondary defence metabolites in many grasses. Over the past years, their role in resistance against insect pests has been studied extensively in maize. However, little is known about how the spatial and temporal variability of BX accumulation in maize leaves determines herbivore feeding patterns. To answer this question, we investigated how BXs shape the foraging behaviour of two insect herbivores, which differ in their degree of host-plant adaptation, on maize plants at different growth stages. Whereas Spodoptera frugiperda was able to tolerate high concentrations of BXs and preferentially fed on younger leaves irrespective of plant age, the generalist Spodoptera littoralis was more susceptible to BXs and showed a clear shift in its feeding behaviour on older plants that contain less BXs. The spatial feeding patterns of S. littoralis were well correlated with the distribution of BXs within the plant. Our results suggest that the defensive investment by the plant determines the feeding patterns of the two herbivores, thereby providing an example of phytochemically driven herbivore behaviour.