While oligophagous and polyphagous insect herbivores may be capable of food-mixing within their lifespans, some individuals are functionally monophagous. Limited access to host plant species may result from dispersal mechanisms that provide little control over destination (such as ballooning), coupled with heterogeneous distributions of host plant species within and between communities. Host plant choice may also be affected by the costs of switching between hosts with different nutritional and allelochemical characteristics. Many populations of the polyphagous moth species Epimecis hortaria live in patchy environments with uneven distributions of host plant species. When combined with neonatal dispersal through ballooning, it is likely that many caterpillars only have access to a single host plant species. We conducted feeding trials on E. hortaria caterpillars to determine the effects of single host plant diets (Liriodendron tulipifera, Asimina triloba, Sassafras albidum, and Lindera benzoin) on caterpillar growth and survival. We measured caterpillar weight and head capsule width at days 12 and 19 after hatching. We also examined caterpillar survivorship, maximum caterpillar weight and pupal weight.
Results/Conclusions
Host plant diet had significant effects on caterpillar growth, maximum caterpillar weight, time until pupation, weight loss during pupation, and maximum pupal weight (p< 0.001). Caterpillars fed on tulip poplar had early rapid growth and developed into large pupae; pupal size was positively correlated with adult weight. Caterpillars fed on pawpaw grew more slowly for a longer time, resulting in the highest maximum caterpillar weights. However, pawpaw caterpillars lost significantly more weight during pupation than any other treatment group (p<0.001), becoming some of the smallest pupae. Although host plant diet affected E. hortaria growth and development, caterpillars in all treatment groups were still able to successfully survive and pupate. Our results demonstrate that E. hortaria polyphagy is not only a result of diet-mixing by individual caterpillars, but provides a range of potential monophagous diets, demonstrating a mechanism by which lepidopteran species may increase larval success in patchy environments.