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

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. Larvae of three lycaenid species (Lycaeides argyrognomon, Lycaena phlaeas and Zizeeria maha) and Pieris rapae possess n‐alkanes as the dominant cuticular hydrocarbons (CHCs), whereas those of Papilio polytes show an alkene‐dominated CHC profile.Formica japonica workers exhibit significantly more frequent biting on Pa. polytes larvae than three lycaenid and P. rapae larvae.Treatments of three lycaenid and P. rapae larvae with authentic alkenes significantly activate ant aggression (biting), which suggests that the absence of alkenes in larval CHCs is effective for circumventing ant predation.