Selaginella and the Satyr: Euptychia westwoodi (Lepidoptera: Nymphalidae) Oviposition Preference and Larval Performance

Members of the plant genus Selaginella (de Beauvois 1805) have few known insect herbivores even though they are considered by some to be ‘living fossils’, with extant taxa virtually indistinguishable from 300 Mya fossils. Butterflies are well-known herbivores, and the satyrs are among the most speciose of them despite having radiated ∼35 Mya ago. Nearly all satyrs feed on grass or sedges, but members of the Neotropical genus Euptychia Hübner 1818 feed on Selaginella; little is known about the degree to which this butterfly favors this ancient plant over those that its close relatives utilize. To advance our knowledge of Euptychia natural history, we conducted a series of experiments to examine oviposition preference and growth rates across a series of potential host plants on a Euptychia westwoodi population in Costa Rica. We found that Euptychia westwoodi Butler 1867 exhibit a strong preference to oviposit on Selaginella eurynota over the sympatric Selaginella arthritica, though they perform equally well as larvae on both plants. We did not observe oviposition on a sympatric grass that is commonly consumed by close relatives of E. westwoodi, and when larvae were offered the grass they refused to eat. These results suggest that E. westwoodi in Costa Rica exhibit a strong preference for Selaginella and may have lost the ability to feed on a locally abundant grass commonly used by other Satyrinae.