Absence of cuticular alkenes allows lycaenid larvae to avoid predation by Formica japonica ants

Abstract

Chemical mimicry and camouflage based on cuticular hydrocarbons (CHCs) are adaptive strategies that are frequently observed in myrmecophilous insects. The larvae of several lycaenid butterfly species that exhibit obligate associations with specific ant species have been reported to use chemical mimicry. However, little is known about the strategies used by the larvae of species that have facultative associations with multiple ant species. We attempted to reveal the effects of larval CHC profiles on interactions with Formica japonica workers, using three lycaenid species, two facultative ant‐associated (Lycaeides argyrognomon and Zizeeria maha) and one non‐ant‐associated (Lycaena phlaeas), which commonly possess n‐alkanes as the major CHCs. In field bioassays, the lycaenid larvae were attacked by ant workers less often than larvae of Papilio polytes (Papilionidae), the CHCs of which were rich in 7‐alkenes. Treating the lycaenid larvae with 7‐heptacosene and 9‐heptacosene significantly activated ant aggression (biting), whereas treating them with n‐heptacosane, n‐octacosane and 13‐methylheptacosane had little effect. Furthermore, larvae of Pieris rapae (Pieridae), possessing n‐alkanes as the dominant CHCs, suffered an intermediate level of ant biting between the lycaenid and Pa. polytes larvae. However, treatments of the P. rapae larvae with 7‐heptacosene and 9‐heptacosene significantly affected the frequency of ant biting. These findings suggest that the absence of alkenes in larval CHC profiles is an effective means of circumventing predation by ants and allows lycaenid larvae to inhabit the foraging territory of predaceous ants, at least to some extent.

Natural Diversity of Cuticular Pheromones in a Local Population of Drosophila after Laboratory Acclimation

“…These properties depend on CHC chemical structure, in particular chain length and number of double bonds [17,18]. CHCs are also involved in protection against harmful external factors (predators, microorganisms, pollutants, xenobiotics and so on) [19][20][21][22]. In many insect species, CHCs are also necessary for inter-individual communication underlying courtship and mating behaviours, territory, nest and trail marking, and aggressive interactions [23][24][25][26][27][28].…”

On the adaptive meaning of chemically insignificant cues in multitrophic caterpillar-ant-plant symbioses

“…Studies with the chemical profiles of myrmecophilous caterpillars with different kinds of interactions with ants (commensalism, mutualism, or parasitism), different degrees of specificity (facultative or obligate), and different feeding habits (herbivorous, omnivorous or carnivorous) have identified several kinds of chemical strategies (e.g. [6,17,28–29]). Thus, myrmecophilous caterpillars are excellent models for studying the ecology and evolution of different chemical strategies mediated by cuticular compounds [30].…”