(a) Adult Pheropsophus occipitalis jessoensis Bombardier beetle. (b) Sirthenea flavipes adult killer bug. Both species are found in the same grasslands in Japan. Credit: Shinji Sugiura
Animals can defend themselves against their natural enemies in various ways. Well-defending species often share clear body colors with other well-defended or unprotected species, forming mimic interactions.
Bombardier beetles spit out toxic chemicals at 100 degrees Celsius to repel enemies like frogs, and many have warning body colors that serve to deter enemies. The killer bug, Sirthenea flavipes, shows distinct body coloration similar to the Bombardier beetle Pheropsophus occipitalis jessoensis that coexists with the killer bug in the same habitat in Japan. The killer bug can stab with its proboscis, causing severe pain to humans. Although well defended by both insects, the mimic interaction between the bombardier beetle and the killer bug remains unclear.
Japanese entomologists Shinji Sugiura (Kobe University) and Masakazu Hayashi (Hoshizaki Green Foundation) found that the bombardier beetle P. occipitalis jessoensis had a stronger defense against a common predator than the killer bug S. flavipes. They also showed that both the Bombardier beetle and the killer bug benefit from a mimic interaction via a co-predator. Their research appears in the June 6, 2023 issue of Berg.
In central Japan, the pond frog Pelophylax nigromaculatus coexists with the Bombardier beetle and the killer bug in the same habitat. Well known as a predator of many insects, the pond frog can attack the bombardier beetle and the killer bug under field conditions. The researchers observed the behavioral response of pond frogs to Bombardier beetles and killer bugs in laboratory conditions.
Among toads, 100% rejected bombardier beetles and 75% rejected killer bugs, indicating that bombardier beetle protects better against toads than killer bugs. The researchers also introduced a bombardier beetle, or killer bug, to a frog that encountered the other insect.
Frogs that did not encounter the Bombardier beetle or killer bug were used in this study. Ignore: Frogs have not attacked beetles (or insects). Stop the attack: Frogs stop their attacks immediately after their tongues touch beetles (or insects). Spit: Frogs spit out beetles (or insects) immediately after taking the indicated insects into their mouths. Credit: Shinji Sugiura
Frogs that had previously encountered one type of insect were less likely to attack other species. Specifically, a history of encounters with killer bugs reduced the attack rate of toads on Bombardier beetles from 75.0% to 21.7%. A history of encounters with Bombardier beetles reduced the toad attack rate on killer bugs from 91.3% to 40.0%. Therefore, the mimic interaction between the bombardier beetle and the killer bug may be mutual.
Attack rates of the Bombardier beetle Pheropsophus occipitalis jessoensis and the killer bug Sirthenea flavipes by the frog Pelophylax nigromaculatus before and after encounters with other insect species. Credit: Shinji Sugiura
more information:
Sugiura, S. & Hayashi, M. Bombardiers and Killers: Mimicking Interactions Among Unevenly Defending Insects., Berg (2023). DOI: 10.7717/ peerj.15380
the quoteBombardier beetle vs. killer bug: simulated interactions across a common enemy (2023, June 6) Retrieved June 6, 2023 from https://phys.org/news/2023-06-bombardier-beetle-assassin-bug-mimetic.html
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