Development and survival of a specialist herbivore, Melitaea cinxia, on host plants producing high and low concentrations of iridoid glycosides

The Glanville fritillary butterfly (Melitaea cinxia) in Finland feeds on the plants Plantago lanceolata and Veronica spicata. These two plant species are distributed heterogeneously and both vary spatially and temporally in iridoid glycoside concentrations. We investigated the associations of plant species and iridoid glycoside (aucubin and catalpol) concentrations with weight, development rate and survival of larvae of the Glanville fritillary under laboratory conditions. In one experiment we compared the performance of split brood groups of larvae feeding on the two plant species collected from natural populations. In the second experiment larvae were fed P. lanceolata lines laboratory selected for high and low aucubin and catalpol concentrations. Larvae fed V. spicata performed better in terms of survival, weight and growth rate than those feeding on P. lanceolata, regardless of iridoid glycoside concentration. However, in the second experiment iridoid glycoside concentration in P. lanceolata was positively associated with larval performance. High iridoid glycoside concentrations retarded development rate of the first instar larvae, whereas later on the development was accelerated by higher concentrations of these compounds. The spatial and temporal variation of plant species suitability and iridoid glycoside content, and larval family level effects of plant chemistry on performance convey a dynamic ecological and evolutionary relationship between these host plants and their specialized herbivore.