Beetle, bombardier

Peschke, K., Schmitt, K., and Zinner, K. (1986). Occurrence of electronically excited products during the defensive reaction of bombardier beetles. Pbotobiochem. Photobiophys. 12 275-282. 

Animals use chemical weapons for both defense and attack. Considering defensive tactics first, bombardier beetles (Brachinus spp.) can fire a hot solution of irritant... 

Agosta, W. (1996). Bombardier Beetles and Fever Trees—A highly readable account of chemical warfare, without much detail on chemical or biochemical aspects. 

Agosta, W. 1996. Bombardier Beetles and Fever Trees. Addison-Wesley, Reading, Massachusetts, pp. 84-89. 

Question 5.9 Why Are Bombardier Beetles Fire-Breathing Dragons ... 

What chemistry is used by bombardier beetles to repel predators ... 

Jeffrey Dean, et al., Defensive Spray of the Bombardier Beetle A Biological Pulse Jet. Science 248 (1990) 1219. 

The Bombardier Beetle. Eric Benson, http //www.wam.umd.edu/-ebenson/brachinus2.html... 

Why are bombardier beetles known as fire-breathing dragons See p. 49. 

The catalysts are enzymes, most of which are proteins. Not only are they catalysts, bnt their catalytic powers are enormous they can increase the rate of a reaction by several orders of magnitnde. Indeed, in the absence of enzymes, life as we know it wonld not be possible. One remarkable example of the nse of the catalytic power of two enzymes in biology is the Bombardier beetle it uses the enormous catalytic power of the enzymes catalase and a peroxidase to deter predators (Box 3.1). 

The Bombardier beetle possesses, at the end of its abdomen, a combustion chamber that contains a hydroqui-none and hydrogen peroxide. When a predator approaches, the cells in the walls of the combustion chamber secrete two enzymes, catalase and peroxidase. Catalase causes decomposition of hydrogen peroxide to produce oxygen peroxidase catalyses the oxidation of the hydroquinone to produce a quinone. 

It is unlikely that the terrorists who, in July 2005, attempted to cause explosions on the London Underground by using a mixture of hydrogen peroxide and flour, obtained the idea of this explosive mixture from a knowledge of the biology of the Bombardier beetle. The mixture failed to explode through failure of the detonators. The secretion of enzymes with their enormous catalytic potential ensures no such failure in the beetle. 

Reservoir and reaction vessel of the bombardier beetle. From D. J. Aneshansley, et al.n... 

The bombardier beetle is an insect of unassuming appearance, measuring about one half-inch in length. When it is threatened by another bug, however, the beetle has a special method of defending itself, squirting a boiling-hot solution at the enemy out of an aperture in its hind section.16 The heated liquid scalds its target, which then usually makes other plans for dinner. How is this trick done ... 

DEFENSIVE APPARATUS OF A BOMBARDIER BEETLE B, COLLECTING VESICLE E, EXPLOSION CHAMBER G, ECTODERMAL GLANDS SECRETING CATALASE L, SECRETORY LOBES M, SPHINCTER MUSCLE 0, OUTLET DUCT. B CONTAINS A MIXTURE OF HYDROQUINONE AND HYDROGEN PEROXIDE, EXPLODED BY CATALASE WHEN IT PASSES INTO E. 

In The Blind Watchmaker Dawkins turns his attention briefly to the bombardier beetle. First he cites a passage from The Neck of the Giraffe, a book by science writer Francis Hitching, that describes the bombardier beetle s defensive system, as part of an argument against Darwinism ... 

The bombardier beetle] squirts a lethal mixture of hydroquinone and hydrogen peroxide into the face of its enemy. These two chemicals, when mixed together literally explode. So in order to store them inside its body, the bombardier beetle has evolved a chemical inhibitor to make them harmless. At the moment the beetle squirts the liquid out of its tail, an antiinhibitor is added to make the mixture explosive once again. The chain of events that could have led to the evolution of such a complex, coordinated and subtle process is beyond biological explanation on a simple step-by-step basis. The slightest alteration in the chemical balance would result immediately in a race of exploded beetles.17... 

Dawkins didn t give us any details of how the bombardier beetle s defensive system might have evolved. To point out the problem with his argument, however, let s use what we know of the beetle s anatomy to build the best possible case for the evolution of the bombardier bee-tie. First, we should note that the function ofthe bombardier beetle s defensive apparatus is to repel attackers. The components of the system are (1) hydrogen peroxide and hydroquinone, which are produced by the secretory lobes (2) the enzyme catalysts, which are made by the ectodermal glands (3) the collecting vesicle (4) the sphincter... 

Thus, to go back to the bombardier beetle and the human eye, the question is whether the numerous anatomical changes can be accounted for by many small mutations. The frustrating answer is that we can t tell. Both the bombardier beetle s defensive apparatus and the vertebrate eye contain so many molecular components (on the order of tens of thousands of different types of molecules) that listing them— and speculating on the mutations that might have produced them—is currently impossible. Too many of the nuts and bolts (and screws, motor parts, handlebars, and so on) are unaccounted for. For us to debate whether Darwinian evolution could produce such large structures is like nineteenth century scientists debating whether cells could arise spontaneously. Such debates are fruitless because not all the components are known. 

Unlike irreducible complexity (where we can enumerate discrete parts), minimal function is sometimes hard to define. If one revolution per hour is insufficient for an outboard motor how about a hundred Or a thousand Nonetheless, minimal function is critical in the evolution of biological structures. For example, what is the minimum amount of hydroquinone that a predator can taste How much of a rise in the temperature of the solution will it notice If the predator didn t notice a tiny bit of hydroquinone or a small change in temperature, then our Dawkins-esque tale of the bombardier beetle s evolution can be filed alongside the story of the cow jumping over the moon. Irreducibly complex systems are nasty roadblocks for Darwinian evolution the need for minimal function greatly exacerbates the dilemma. 

Eisner, T Attygalle, A. B., Eisner, M., Aneshansley, D. J., and Meinwald, J. (1991) Chemical Defense of a Primitive Australian Bombardier Beetle (Carabidae) Mystropomus regularise Chemoecology, 2, 29. 

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