Facultative defences and specialist herbivores? Cinnabar moth (Tyria jacobaeae) on the re growth foliage of ragwort (Senecio jacobaea)

Abstract

Abstract. 1. Ovipositing females of cinnabar moth lay just as many eggs on regrowth foliage as on normal rosette leaves of ragwort.2. Larvae reared on regrowth tissues achieve the same weight at pupation as insects fed on primary leaves and capitula. Diet affected neither survival rate nor development time.3. Larvae from eggs laid on normal foliage achieve lower pupal weights when fed regrowth tissues, and larvae from eggs laid on regrowth leaves perform less well on a diet of normal foliage.4. The complex of changes associated with re growth following defoliation does not appear to reduce the fitness of this specialist herbivore, nor does it reduce the likelihood that the plant will be attacked by ovipositing adult moths.5. A facultative response which consisted of an increase in ‘qualitative defences’ is unlikely to be effective against adapted herbivores.