Does group feeding by toxic prey confer a defensive benefit? Aristolochic acid content, group size and survival of first‐instar pipevine swallowtail (Battus philenor L.) larvae. (27th May 2019)

• Record Type: Journal Article
• Authors: Wilmoth, Lauren W.; Fordyce, James A.
• Is Part Of: Ecological entomology. Volume 44:Number 6(2019)
• Page Start: 745
• Page End: 752
• Publication Date: 2019-05-27
• Subjects: Aggregative feeding -- caterpillar -- chemical defence -- gregarious -- predation -- sequestration; Insects -- Ecology -- Periodicals; Entomology -- Periodicals; 595.7
• DOI: 10.1111/een.12753
• Languages: English
• ISSNs: 0307-6946

Abstract

Abstract : 1. Aggregative feeding of larvae is widespread in the Lepidoptera, and many hypotheses have been proposed to explain the adaptive significance of this trait. Group feeding occurs disproportionately more in species with aposematic, chemically defended larvae compared with species with cryptic, non‐chemically defended larvae, consistent with the hypothesis that group feeding provides an enhanced aposematic signal to natural enemies. Most species characterised as having chemically defended larvae are cryptic during the first instar, when they are most highly aggregated and most vulnerable to predation. 2. The benefits of group feeding in terms of decreased predation were explored for first‐instar larvae of the pipevine swallowtail, Battus philenor, a species that sequesters aristolochic acids from its Aristolochia host plant and exhibits aposematism in later instars and as adults. We found that groups of larvae with experimentally enhanced aristolochic acid content had significantly lower survivorship due to predation both in the field and in laboratory experiments compared with groups of larvae without enhanced chemical defence. 3. A laboratory experiment found that aristolochic acid does not deter the generalist predator Hippodamia convergens . 4. No evidence was found that was consistent with the hypothesis that group feeding and increased sequestered chemical defence interact to decrease rates of larval mortality in non‐aposematic, first‐instar larvae. Future research on chemical defence, aposematism, and aggregative feeding should continue to appreciate that particular chemical defences and feeding behaviours are not universally effective against all natural enemies. Abstract : Aggregative feeding is widespread among larvae of Lepidoptera that are chemically defended, and a common adaptive explanation for this behaviour is that group feeding augments chemical defence and reduces larval mortality. Group feeding by first‐instar pipevine swallowtail larvae provided no additional defensive benefit against natural enemies in both field and laboratory experiments. Increased larval chemical defence resulted in higher mortality for caterpillars feeding in groups than for larvae feeding singly.