Dynamics of host plant selection and host-switching by silver-spotted skipper caterpillars

Investigations of host plant selection in herbivorous arthropods have emphasized the importance of oviposition site selection by adults; however, a more complete picture of this process requires additional consideration of the factors influencing host plant choice during the immature feeding stages. We conducted a series of larval choice experiments to examine both the innate and induced preferences of larvae of the Silver-spotted skipper (Epargyreus clarus L.) on three commonly used hosts (Wisteria, Robinia, and Pueraria). Late instar E. clarus larvae reared on each of the three host plants displayed an overall pattern of innate preferences that correlated well with larval performance measures and reflected differences in foliar nutrient concentrations. Larval preferences were also influenced by rearing host species, indicating a role for feeding-induced preferences. When larvae reared on low-quality Wisteria for the first four instars were switched to higher quality Pueraria for the final instar, they developed more quickly and attained significantly higher pupal mass than larvae maintained on Wisteria throughout development. Similarly, larvae switched from Pueraria to Wisteria for the final instar suffered increased development time and produced significantly smaller pupae than those maintained on Pueraria throughout. Thus host-switching, particularly during the more mobile final instars, appears to offer larvae an opportunity to recoup fitness losses associated with early development on a low-quality host. For an equal amount of consumption, larvae feeding on Pueraria gained 50% more mass than those feeding on Wisteria, reflecting measured differences in foliar nitrogen concentration; despite these overall differences in quality, larval growth efficiency was similar among hosts. Especially in the age of common exotic plant introductions, a full understanding of the behavioral component of host selection by herbivorous insects requires appreciation of the dynamic role that immatures can play in host selection and use.