Host‐plant Relationships in the Papilionidae (Lepidoptera): Parallel Cladogenesis or Colonization?

Stepwise coevolution, as defined by Ehrlich and Raven (1964) and others, can be equated with parallel cladogenesis or association by descent (Mitter and Brooks, 1983). I review the insect/plant literature and discuss recent cladistic findings for the Papilionidae, and compare two contrasting theories: 1) that insect/host associations have evolved through parallel cladogenesis; or 2) that insects have 'colonized' their hosts subsequent to plant cladogenesis. I conclude that no documented examples of parallel cladogenesis between insects and plants are known. The swallowtail cladograms instead offer evidence in support of the second theory. They suggest that host association patterns in the Papilionidae have resulted from repeated colonization of plants belonging to a relatively small number of families. I discuss data which indicate that plant secondary chemicals have been important 'barriers' to colonization (sensu Ehrlich and Raven, 1964), and have in large part mediated host switching in the Papilionidae.