Do canal-cutting behaviors facilitate host-range expansion by insect herbivores?

According to the escalation-radiation model of coevolution, insect herbivores that acquire the ability to circumvent a plant defense enter a new adaptive zone and increase in species. How herbivore counteradaptations to plant defenses might lead to speciation is poorly understood. Studies of nymphalid butterflies suggest that the evolution of broadened host range may be a critical step. This paper examines if leaf-feeding insects capable of deactivating defensive plant canals with canal-cutting often have broad host ranges. A total of 93 species of canal-cutting insects were identified from the literature, including nine new canal cutters. Only 27% of canal cutters with known host ranges are generalists that feed on plants in multiple families. The proportion of generalist canal cutters is similar or lower than estimates of generalists among phytophagous insects overall. Only five species, at most, of the canal-cutting generalists feed exclusively on plants with secretory canals. The paucity of generalists can be attributed in part to the considerable taxonomic distance separating canal-bearing plant families and their corresponding chemical distinctiveness. The dependence of many canal-cutting species on host chemicals for defense would also favor specialization.