Size discrimination among conspecific hostplants in two pierid butterflies; Pieris napi L. and Pontia daplidice L.

Females of the butterflies Pieris napi and Pontia daplidice discriminate against large hostplant individuals, usually preferring low rosettes or seedlings, when hostplants are abundant. In this paper the larval mobility between young hostplant, and differences in survival and growth rate on low versus tall conspecific hostplants were studied in these two species in Sweden. The results suggest that the largest effect of plant size is that small plants support faster growth than bigger ones. This seems to be due to differences in microclimate conditions, not an effect of different suitability as food. Thus, on the assumption that there are no systematic differences in larval death rate, which is supported by the results in this study, preference for small hostplants should be advantagous, leading to higher survival during development, and higher probability for an additional brood per year.