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Mechanistic origins of bombardier beetle (Brachinini) explosion-induced defensive spray pulsation

Science  01 May 2015:
Vol. 348, Issue 6234, pp. 563-567
DOI: 10.1126/science.1261166

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A beetle's internal bomb

Bombardier beetles shoot a toxic pulse at potential predators and other harassers. The toxic spray is created by a chemical reaction that occurs inside the beetle's body. Although the details of the reaction are known, how the beetle is able to precisely combine the chemicals at appropriate times and release the pulse at regular intervals has remained a mystery. Arndt et al. used synchrotron x-ray imagery to observe the process as it occurs within live beetles. Expansion and contraction of an internal expansion membrane facilitate the precise cyclic injection of reactants and the subsequent ejection of toxic sprays that keep the beetle's predators at bay.

Science, this issue p. 563

Abstract

Bombardier beetles (Brachinini) use a rapid series of discrete explosions inside their pygidial gland reaction chambers to produce a hot, pulsed, quinone-based defensive spray. The mechanism of brachinines’ spray pulsation was explored using anatomical studies and direct observation of explosions inside living beetles using synchrotron x-ray imaging. Quantification of the dynamics of vapor inside the reaction chamber indicates that spray pulsation is controlled by specialized, contiguous cuticular structures located at the junction between the reservoir (reactant) and reaction chambers. Kinematics models suggest passive mediation of spray pulsation by mechanical feedback from the explosion, causing displacement of these structures.

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