Evolutionary ecology of host use in the silver spotted skipper
Developing our understanding of the ecological factors shaping patterns of host plant use in herbivorous insects is a major goal of insect ecologists. Previous studies of host shifts in specialist herbivores have suggested that reduced enemy pressure for herbivores feeding on novel hosts can facilitate these diet expansions. The role of enemies in facilitating or maintaining diets of generalists is less clear. Introductions of exotic plants for human use in agriculture and horticulture present unique opportunities to investigate the dynamics of host range expansion in native insects. In this talk, we report early results of an ongoing project investigating the evolutionary and behavioral ecology of host selection in a common butterfly, the silver-spotted skipper (Epargyreus clarus). As caterpillars, these skippers oviposit and feed on a variety of leguminous hosts, which include both native (black locust, hog-peanut, and tick-trefoil) and non-native (Chinese wiseria, soybean, and kudzu) plants. We examined both adult oviposition preference and larval performance of E. clarusin the presence and absence of enemies, utilizing a common garden enviornment over two generations in 2014.
Oviposition trials with this skipper indicated differential host selection by adult females and no-choice feeding assays in the laboratory revealed strong host plant effects on multiple measures of caterpillar performance (survival, development time, pupal mass). Field trials using bagged caterpillars that were protected from natural enemies were generally consistent with lab performance findings, whereas exposed larvae subject to predation and parasitism were considerably more variable in host plant rankings. Across all host plants, both development time and predation was higher in the second generation than the first. There was no evidence of ecological tradeoffs maintainig host in the first year of support, lending greater suppor to bet-hedging models of host use in a temporally unpredictable landscape.