Trade‐offs in responses to host plants within a population of a generalist herbivore, Choristoneura rosaceana

Evolutionary constraints on the ability of herbivores to efficiently use a set of phytochemically similar hosts, while maintaining a high performance on phytochemically different hosts, are central in explaining the predominance of host specialization in phytophagous insects. Such feeding trade‐offs could be manifested within insect populations as negative genetic correlations in fitness on different host species. We tested the hypothesis that feeding trade‐offs were present within a population of the obliquebanded leafroller, Choristoneura rosaceana (Harris). Components of fitness were measured in families originating from an apple orchard that were fed on four host‐plant species in the laboratory. Under the conditions of this experiment, all across‐host genetic correlations were strongly positive, suggesting that this population comprised true generalists. With the exception of diapausing propensity, the heritability of the fitness components tended to be lower in caterpillars fed on apple leaves than in insects fed other hosts. This suggests a constraint on the selective response of the fitness components in the orchard environment. 1994 The Netherlands Entomological Society