Antipredator strategies of pupae: how to avoid predation in an immobile life stage?

Abstract

Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be 'avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue 'The evolution of complete metamorphosis'.

Keywords: chemical defence; physical defence; predator–prey interactions; protective coloration; pupal defence.

Figure 1.

Insects have evolved an extensive diversity of protective coloration strategies in the pupal stage, although their function and mechanisms have largely remained unstudied. (a) Pupae of the Peacock butterfly (Aglais io) are well camouflaged. (b) Pupae can also masquerade themselves to resemble something uninteresting to potential predators such as leaf-mimicking chrysalises of the Common Maplet butterfly (Chersoneria risa). (c) In some species, such as Harlequin ladybird (Harmonia axyridis), pupae may advertise their defensive toxins with conspicuous warning colours. (d) Pupae can also have shiny coloration such as chrysalides of the Common Crow butterflies (Euploea core), which could both function as a warning signal or conceal the pupa from the predator's eye. (Photos: a–d Adobe Stock.)

Figure 2.

Pupae can defend against predators with different kinds of morphological and chemical defences or even rely on protection from other individuals. (a) Aposematic Heliconius melpomene butterflies' pupae are covered with spines. (b) Many moth species produce a silk cocoon or loose silk nets to protect the pupa (white satin moth, Leucoma salicis). (c) Larval, pupal and adult stage in the common buckeye (J. coenia) contain iridoid glycosides that give them chemical protection predators. (d) Maculinea rebeli butterfly pupae use vocal communication to recruit ants to guard them. (Photos: a–c Adobe Stock, D. Marco Gherlenda.)