Generalist-feeding animals must overcome a wide range of defenses in the species that they consume. In particular, structural feeding barriers in plants pose major challenges to generalist herbivores, and it is unclear what adaptations enable them to surpass these barriers. Understanding the feeding strategies used by generalist herbivores, as well as their limitations, is important for predicting future range shifts of introduced species as well as other species of economic or ecological concern. We investigated how two strategies, developmental plasticity and social feeding behavior, may contribute to diet breadth in western leaf-footed bugs, Leptoglossus zonatus (Hemiptera: Coreidae). To test the role of plasticity in diet breadth, we raised bugs on a diet of sunflower seeds covered with either a thin or a thick artificial coating and measured their mouthpart morphology at adulthood. We found that bugs raised on seeds with a thick coating had relatively longer mouthparts, indicating likely diet-induced plasticity. To test how social behavior contributes to diet breadth, we raised bugs with either an adult or a juvenile conspecific on a diet of pecans with or without shells. Juvenile bugs may reuse the feeding sites of larger conspecifics to facilitate feeding through barriers. We therefore predicted that bugs feeding on pecans with shells would have higher survival when housed with an adult than with another juvenile. Surprisingly, we found that juvenile survival was severely limited by pecan shells and the presence of adults did not ameliorate this effect. Our results suggest that morphological plasticity, but not social behavior, facilitates feeding and could function to maintain diet breadth in L. zonatus.