Cycads are an ancient group of tropical gymnosperms that are toxic to
most animals—including humans—though the larvae of many moths and
butterflies (order: Lepidoptera) feed on cycads with apparent immunity.
These insects belong to distinct lineages with varying degrees of
specialization and diverse feeding ecologies, presenting numerous
opportunities for comparative studies of chemically-mediated
eco-evolutionary dynamics. This review presents an evolutionary
evaluation of cycad-feeding among Lepidoptera along with a comprehensive
review of their ecology. Our analysis suggests that multiple lineages
have independently colonized cycads from angiosperm hosts, yet only a
few clades appear to have radiated following their transitions to
cycads. Defensive traits are likely important for diversification, as
many cycad specialists are warningly colored and sequester cycad toxins.
The butterfly family Lycaenidae appears to be particularly predisposed
to cycad-feeding and although aposematism is otherwise rare in this
family, several cycad-feeding lycaenids are warningly colored and
chemically defended. Cycad-herbivore interactions provide a promising
but underutilized study system for investigating plant-insect
coevolution, convergent and divergent adaptations, and the multi-trophic
significance of defensive traits, therefore the review ends by
suggesting specific research gaps that would be fruitfully addressed in
Lepidoptera and other cycad-feeding insects.