Defense chemicals secreted by Ardistomis schaumii beetles can pass directly through the exoskeletons of their foes with the aid of special solvents.

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Delivering defensive chemicals to a foe is a challenge for all organisms that synthesize such chemicals. Many strategies have evolved in nature including aerosolization, hypodermic injection, etc. Ardistomis schaumii beetles have developed a delivery method that involves dissolving the defensive chemicals in a solvent called limonene. Limonene, a non-polar solvent, is somehow able to facilitate the transport of polar defensive chemicals through the non-polar exoskeleton of predatory arthropods. Though the precise chemical mechanism is still unclear, the advantage is obvious; A. schaumii can deliver repellants directly into the bodies of their foes rather than attacking sensory organs like many repellants.

This summary was contributed by Ashley Meyers

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"Information on the defensive chemistry of over 500 carabid species show that their defensive secretions consists mainly of hydrocarbons, acids, quinones, aliphatic ketones, and aldehydes, and a variety of other organic compounds." (Attygalle et al. 2009:1443)

"Limonene, a well-known constituent in essential oils of several plants, is known to function as an insect repellent as well as a repellent of some birds and mammals such as deer." (Attygalle et al. 2009:1446)

"Many arthropods use benzoquinones as repellents. It is also known that benzoquinones are generally accompanied by hydrocarbons which have been speculated to serve as solvents for uptake of the quinones which are crystalline at room temperature. Apparently nonpolar compounds facilitate the transport of active polar compounds through the waxed epicuticle of enemy arthropods. It is very likely that limonene acts as a permeation enhancer for benzoquinone. For example, it has been demonstrated that the transdermal delivery of acetylsalicylic acid, a potent antithrombotic drug, via skin patches can be significantly improved by admixing it with limonene." (Attygalle et al. 2009:1448)

Journal article
Orange/lemon-scented beetles: opposite enantiomers of limonene as major constituents in the defensive secretion of related carabidsNaturwissenschaftenAugust 18, 2009
Athula B. Attygalle, Xiaogang Wu, David R. Maddison, Kipling W. Will

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