1. Past studies of plant–phytophage communities have encountered both nested and modular/compartmented food web structures, revealing potentially important differences in the nature of interactions.
2. We analysed qualitatively and quantitatively a taxonomically resolved plant–hispine beetle food web from Panama (lower Central America) to characterise its structure. The study included all beetles in the subfamily Cassidinae (Chrysomelidae) found feeding on common monocotyledonous plants in the Tropical forest understorey and edge habitats.
3. Nestedness, a structural property common to many food webs, was not observed in this study, however strong evidence for a modular structure was uncovered.
4. Our findings suggest the feeding niches of hispine beetles are constrained within module boundaries, which largely correspond to plant ordinal and familial limits, and secondarily to plant attributes, including the morphology of immature leaves.
5. We conclude that modularity in this food web is largely a product of narrow, discrete hispine beetle host specificity for larger phylogenetically related plant taxa.