Effect of hostplant genotype and predators on iridoid glycoside content of pupae of a specialist insect herbivore, Junonia coenia (Nymphalidae)

Abstract

Abstract Two field experiments assessed the effects of hostplant genotype, presence or absence of predators, and type of predator on chemical content of pupae of the Buckeye butterfly, Junonia coenia (Nymphalidae). When fed Plantago lanceolata (Plantaginaceae), J. coenia larvae sequester two iridoid glycosides, aucubin and catalpol, which are retained into the pupal stage. In the first experiment, it is found that hostplant genotype significantly affected iridoid glycoside content of pupae, but although the predatory stinkbugs ( Podisus maculiventris : Pentatomidae) caused the larvae to alter their foraging behavior, pupal iridoid glycoside content was not influenced by the presence or absence of the predators. In the second experiment, it is found that the kind of predator present had an effect on chemical defense of pupae: pupae exposed as larvae to stinkbugs had a higher proportion of catalpol than pupae exposed as larvae to wasps, Polistes fuscatus (Vespidae). Furthermore, pupae from both experiments contained higher proportions of catalpol than that available in the plants on which larvae fed. Therefore, the conditions under which herbivorous larvae develop, such as hostplant genotype eaten and type of natural enemies present, can affect their chemical content.