Does group feeding by toxic prey confer a defensive benefit? Aristolochic acid content, larvae group size and survival of pipevine swallowtail (Battus philenor) larvae.

• Main Author: Wilmoth, Lauren Wisner
• Format: Others
• Published: Trace: Tennessee Research and Creative Exchange 2011
• Subjects: Gregariousness; Trade-off; Hippodamia convergens; Aggregation; Battus philenor; Aristolochic acid; Behavior and Ethology; Ecology and Evolutionary Biology
• Online Access: http://trace.tennessee.edu/utk_gradthes/924

Aggregative feeding is widespread in Lepidopteran larvae suggesting that this behavior serves on adaptive function. Many studies of the potential benefits of aggregative feeding in Lepidopteran larvae have been conducted. However, no studies have directly examined the benefits of cryptic larvae being both chemically defended and gregarious. Group feeding occurs disproportionately more in chemically defended larvae than in larvae that have no chemical defense. Most of these larvae are cryptic when they are most highly aggregated and most vulnerable to predation. In this study, the benefits of group feeding in terms of decreased predation were explored in first instar larvae of pipevine swallowtail larvae, Battus philenor, a species that exhibits chemical sequestration. Contrary to our expectation, we found that groups of larvae fed a diet with high levels of the toxin aristolochic acid, which they sequester naturally and use as a defense against natural enemies, had significantly lower survivorship due to predation in both the field and in the laboratory experiments compared to groups of larvae fed a diet with low aristolochic acid content. We also found that aristolochic acid does not deter the generalist predator Hippodamia convergens, the ladybird beetle, suggesting that this compound is not a universal predator deterrent as previously assumed. Thus, instead of finding a benefit to group feeding and chemical defense in cryptic larvae, we have found a negative impact of group feeding in this population of B. philenor. Based on this evidence, we speculate that other benefits of group feeding might be outweighing the negative consequences of increased predation during the first instar. Future research on chemical defense, aposematism, and aggregative feeding should take into consideration that chemical defenses might not be universally effective against all natural enemies.