Ecological tradeoffs in host plant use by the silver-spotted skipper, Epargyreus clarus

Explaining patterns of host plant use by phytophagous insects is a major goal of researchers studying plant-herbivore interactions. Fitness tradeoffs on alternative host plants have been implicated in recent host range expansions and as such, may represent an important evolutionary force in insect diet evolution. To test this proposition, we quantified silver-spotted skipper (Epargyreus clarus) oviposition preference for and larval feeding preference and performance on one native host (black locust, Robinia pseudoacacia) and two naturalized exotic hosts (kudzu: Pueraria lobata and wisteria: Wisteria sinensis). Performance was examined both in the absence and presence of natural enemies. Oviposition choice tests indicated that kudzu and black locust were equally preferred hosts for adults (52 and 46% of total eggs laid), whereas wisteria was largely avoided (< 2% of eggs).  Feeding choice tests with E. clarus larvae produced similar results, except that larvae showed a slight preference for black locust over kudzu, both of which were strongly preferred over wisteria.  In no-choice laboratory feeding trials, larvae developed more quickly on black locust but produced larger pupae on kudzu, suggesting a potential fitness tradeoff between these two equally preferred host plants. Wisteria was a relatively poor quality food for E. clarus in feeding trials, with larvae developing significantly more slowly and producing, on average, the smallest pupae relative to the other two host plants. In the field, however, larval survival was highest on wisteria relative to the two preferred hosts in some trials, suggesting a role for enemy-free space in promoting and/or maintaining the inclusion of this host in the diet of local populations of E. clarus.