Intraspecific variation in feeding preference and performance of Galerucella nymphaeae (Chrysomelidae:Coleoptera) on aquatic macrophytes

The feeding preferences and performance of a freshwater macrophyte-feeding chryso­melid beetle (Galcruccl/a nymplzacac) were assessed in laboratory experiments. Populations of Galerncella had a relatively narrow diet breadth, preferring species of Nuphm; Polt1gonum, and in 1 case Brasenia, while largely ignoring the remaining macrophytes offered in assays. However, because of interpop­ulation variation in host preferences, the species G. nymplzacae should be considered polyphagous. Distant populations from the Upper Peninsula of Michigan, Indiana, and North Carolina collected from ,'\J11plrnr spp. all readily consumed Nuplzar spp. and Polygonum spp., but beetles from a site in south '.'vlichigan collected from P a111phi/ii11111 or from Brasrnia schreberi treated Nuphar as a low-pref­erence host. The performance of Galcrucella in no-choice assays was clearly related to the behavioral preferences of the larvae: larvae performed well on 3 macrophyte species that they willingly con­sumed, but performed poorly when they refused to consume alternative host plants and presumably starved to death. It is unknown if the starved beetles could have performed well physiologically if they had eaten alternative hosts. Performance was also related to the quality of host plant, given that beetles collected from ,'-.'11plw1· luteum or N. ad,nw reached a larger adult mass on N. l11teum than on N. ad,nza. The feeding preferences of Galcrncclla were largely non-plastic within a single generation, although there were sometimes behavioral differences among clutd1mates raised on different host plants. \1orphometric and prcliminarv allozvme data suggest the North American populations used in this paper are conspecific, but they probably represent a different species than European G. nym­phacat. The intraspecific variation of our North American G. nymp!rneae in host preferences and per­formance suggests that at least 2 different ecotypes occur in North America.