Spatial and temporal patterns of caterpillar performance and the suitability of two host plant species

Abstract

1. The butterfly Melitaea cinxia uses two host plant species in the Åland Islands of south-west Finland. Survey data show that host plant use is spatially variable and that the two species are not used (fed on by M. cinxia larvae) in proportion to their abundances. The pattern of host plant use by M. cinxia has been attributed in part to plant distribution and spatial variation of butterfly oviposition preference. 2. The additional roles that may be played by spatial variation in host plant quality and larval physiology (performance ability) were investigated. Seven years of field survey data and a series of laboratory experiments were used to demonstrate that neither of these variables contributed measurably to the observed pattern of host plant use. 3. Specifically, while there was great variation among individuals in both the performance ability of caterpillars and host plant suitability, the two plant species appeared equally suitable, there was no within-species geographic variation in plant suitability, and there was no evidence for adaptation of caterpillars to the locally used host plants.