Ecological determinants of host plant use by fall webworm

The factors governing host plant use in generalist insect herbivores are poorly known.  With the broad array of potential host plants available, how do generalists choose among them?  To begin to address these questions, this research examined fall webworm (Hyphantria cunea Drury), a highly polyphagous moth in the family Arctiidae that feeds on over 600 woody plant species worldwide, with variable local preference patterns.  Field surveys of oviposition sites in the greater Washington DC area accompanied by genetically-controlled laboratory feeding trials sought to understand the relationship between preference and performance on a variety of host plants. Larval host plant had a strong effect on all herbivore performance measures examined and the rankings of host plant suitability did not vary among full-sib families. From the biotrophic perspective, no apparent tradeoffs exist among performance measure on alternative hosts indicating that populations should be under selection to specialize on the highest quality hosts. However, host use patterns observed in the field did not predict performance in the laboratory for any fitness measures.  Larvae were found to be feeding on the most common host plants at rates higher than would be expected by chance, suggesting female fall webworm are choosing ovipostion sites strongly based upon local abundance of potential host plants.  Plant nutritional quality, often described as a key component in host plant selection for polyphagous insects, appeared to play only a mild role in host plant selection, suggesting other factors (i.e., host plant difference in attack from the third trophic level) may play a role in local patterns of host use.