Bombardiers and assassins: mimetic interactions between unequally defended insects.

In defensive mimicry, resemblance between unequally defended species can be parasitic; this phenomenon has been termed quasi-Batesian mimicry. Few studies have used real co-mimics and their predators to test whether the mimetic interactions were parasitic. Here, we investigated the mimetic interaction between two well-defended insect species, the bombardier beetle (Coleoptera: Carabidae) and the assassin bug (Hemiptera: Reduviidae), using their potential predator, the pond frog (Anura: Ranidae), which coexists with these insect species in the same habitat in Japan. We observed behavioural responses of this frog species (adults and juveniles) to adult . and adult . under laboratory conditions. Among the frogs, 100% and 75% rejected . and . , respectively, suggesting that, compared with the assassin bug . , the bombardier beetle . is more well-defended against frogs. An assassin bug or a bombardier beetle was provided to a frog that had encountered the other insect species. Frogs with a history of assassin bug encounter demonstrated a lower rate of attack toward bombardier beetles. Similarly, frogs with a history of bombardier beetle encounter demonstrated a lower rate of attack toward assassin bugs. Therefore, both the bombardier beetle . and the assassin bug . benefit from the mimetic interaction.