The genetic basis of host plant use by phytophagous insects can provide insight
into the evolution of ecological niches, especially phenomena such as
specialization and phylogenetic conservatism. We carried out a quantitative
genetic analysis of multiple host use traits, estimated on five species of host
plants, in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera:
Chrysomelidae). Mean values of all characters varied among host plants,
providing evidence that adaptation to plants may require evolution of both
behavioral (preference) and post-ingestive physiological (performance) char-
acteristics. Significant additive genetic variation was detected for several
characters on several hosts, but not in the capacity to use the two major hosts,
a pattern that might be caused by directional selection. No negative genetic
correlations across hosts were detected for any ‘performance’ traits, i.e. we
found no evidence of trade-offs in fitness on different plants. Larval
consumption was positively genetically correlated across host plants, suggest-
ing that diet generalization might evolve as a distinct trait, rather than by
independent evolution of feeding responses to each plant species, but several
other traits did not show this pattern. We explored genetic correlations among
traits expressed on a given plant species, in a first effort to shed light on the
number of independent traits that may evolve in response to selection for
host–plant utilization. Most traits were not correlated with each other,
implying that adaptation to a novel potential host could be a complex,
multidimensional ‘character’ that might constrain adaptation and contribute
to the pronounced ecological specialization and the phylogenetic niche
conservatism that characterize many clades of phytophagous insects.