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Termites explode to defend their colony

July 26, 2012 This article courtesy of Nature News.

Species uses chemical reaction to drive toxicity of their "explosive backpacks".

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A species of termite in the rainforests of French Guiana takes altruism to the next level: by growing sacks of toxic blue liquid that they explode onto their enemies in an act of suicidal self-sacrifice.

The “explosive backpacks” of Neocapritermes taracua, described in the journal Science today, grow throughout the lifetime of the worker termites, filling with blue crystals secreted by a specialised pair of glands on their abdomens. Older workers carry the largest and most toxic backpacks. Those workers also, not coincidentally, have dull and worn mandibles, which the insects are unable to sharpen by molting.

“Older individuals are not as effective at foraging and nest maintenance as younger workers – in this moment they can provide another service to the colony,” says lead author Robert Hanus of the Academy of Sciences in the Czech Republic. “It makes perfect sense to me because theories predict that social insects should perform low risk, laborious tasks such as house keeping in the first part of their life and to perform risky tasks such as defense as they age.”

Self-destructive behaviour is common among the sterile worker castes of social insects like termites and honeybees, who are free to evolve specialised altruistic behaviours that benefit the colony as a whole. Defensive suicidal rupturing – termed “autothysis” – has evolved independently in a number of termite species, suggesting that the behaviour is highly adaptive.

Other species of termites illustrate how these explosive backpacks would evolve, says Hanus. Many species simply defecate onto their enemies, and can do so from a considerable distance with remarkable accuracy. Other species go a step further, by actively squeezing their abdominal muscles until they explode; these species have developed a portion of abdominal wall which is thinner and weaker, primed to rupture. In the next stage of suicidal rupturing, some species of termites have evolved specialised glands that produce a toxic chemical which is more harmful to enemies than mere intestinal waste.

N. taracuahas added a new chapter to the story of termite suicide, by using a chemical reaction to make their defensive chemical more toxic. Their two specialised glands produce copper-containing blue crystals, which are gathered in a pair of pouches. When the termites explode, these pouches burst alongside the salivary glands. The crystals must react with secretions from the salivary glands in order to become toxic.

“It is the two component chemistry which underlies the exceptional toxicity in this species,” says Hanus.

The Czech researchers dosed the bodies of an enemy termite species with blue liquid from the older workers, white liquid from younger workers, liquid from the younger workers that had been treated with blue crystals, and liquid from the older workers with the blue crystal removed. The blue liquid from older workers proved the most toxic, followed by the while liquid which had been treated with blue crystals.

“The sophistication of this is remarkable: we have never seen an external pouch like this before that adds one substance which needs to be mixed with another substance,” says Olav Rueppell of North Carolina State University, who studies social evolution and honey bees. “This kind of adaptation would not evolve in a solitary context; this shows the power of eusociality, and why these insects are so successful.”


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