Mimetic interactions through common enemies

Animals can defend themselves against their natural enemies in various ways. Species that are well protected often share striking body colors with other species that are well protected or not, forming mimetic interactions. Bombardier beetles secrete toxic chemicals at 100°C to ward off enemies such as frogs, and many have warning body colors that serve to deter enemies. killer bug, Sirthene flavipesshow a striking body color similar to the bombardier beetle Pheropsophus occipitalis jessoensis that coexisted with assassin insects in the same habitat in Japan (Fig. 1). The killer bug can stab with its proboscis, causing severe pain to humans. Although these two insects survive well, the mimetic interactions between bombardier beetles and killer bugs remain unclear.

Japanese entomologists Shinji Sugiura (Kobe University) and Masakazu Hayashi (Hoshizaki Green Foundation) found that the bombardier beetle P. jessoensis occipitalis have a stronger defense against common predators compared to killer bugs S. flavipes. They also show that bombardier beetles and assassin insects benefit from mimetic interactions through shared predators. Their research appears in the June 6, 2023 issue FriendJ.

In central Japan, pond frogs Pelophyllax nigromaculatus coexist with bombardier beetles and killer insects in the same habitat. Pond frogs, which are known as predators of various insects, have the potential to attack bombardier beetles and killer insects in field conditions. Researchers observed the behavioral responses of pond frogs to bombardier beetles and assassin insects in laboratory conditions (see video). Among the frogs, 100% repelled the bombardier beetles and 75% rejected the killer bugs (Fig. 2), indicating that the bombardier beetles defended better against the frogs than the killer bugs. The researchers also gave bombardier beetles or killer bugs to frogs that encountered other insects. Frogs that had previously encountered one insect species were less likely to attack another species (Fig. 3). In particular, history of encounters with killer bugs reduced the attack rate of bombardier frogs from 75.0% to 21.7% (Fig. 3). Historical encounters with bombardier beetles reduced the killer toad attack rate by frogs from 91.3% to 40.0% (Fig. 3). Therefore, the mimetic interactions between bombardier beetles and killer insects may be mutualistic.

Videos:
https://youtu.be/BZ75K6rfvdE
Credit: Shinji Sugiura

Journal article:
Sugiura, S. & Hayashi, M. (2023) Bombardiers and assassins: mimetic interactions between defense-imbalanced insects. FriendJ (https://doi.org/10.7717/peerj.15380)