Some insects have developed incredible abilities in the course of evolution that help them survive in certain conditions and protect themselves from predators. For example, kamikaze termites carry “backpacks” filled with a toxic substance. In an emergency, they explode, allowing them to destroy their enemies with “chemical weapons”. For a long time, scientists were puzzled by how they managed to carry “chemical weapons” safely for themselves, but use them at the right time. Thanks to a recent study, this mystery was solved.
A kamikaze termite carries a “backpack” with toxic substances. Photo source: phys.org
Kamikaze termites are “running chemical bombs”
Kamikaze termites (Neocapritermes taracua) are also called “running chemical bombs” due to their explosive behavior. Scientists discovered this ability relatively recently, in 2012. As reported in a study published in the journal Science, worker termites Neocapritermes taracua develop a two-component suicide apparatus consisting of copper-containing protein crystals.
The chemical is contained in external blue sacs. Glands in the abdominal cavity are responsible for its production. The amount of protective substances, and at the same time the readiness to explode, increases with age in termites. When termites are threatened, they blow up themselves and any enemies that are nearby.
When they explode, the enzymes in the “backpacks” mix with relatively harmless secretions produced in their salivary glands. When the two components mix, a sticky liquid with extremely toxic volatile substances is formed. These substances can immobilize or kill predators. Of course, the termite itself also dies in the process.
Kamikaze termites kill themselves to protect the colony. Photo source: phys.org
Scientists call this behavior autothysis, or suicidal altruism. This name is associated with the fact that the insect destroys itself to get rid of enemies, and thus protect other individuals in the population.
It should be noted that Neocapritermes taracua is not the only species that has such abilities. Vietnamese termites of the Globitermes sulphureus species, as well as Serritermes serrifer, Dentispicotermes and some other species are also known for their suicidal altruism. However, in many species, such as Globitermes sulphureus, not all individuals have the ability to blow themselves up, but only the soldier caste.
How Termites Use Explosive “Backpacks”
It remained a mystery to scientists how the BP76 enzyme, which accumulates in the sacs, remains solid on the backs, but is ready to react instantly in case of danger. This mystery was solved by studying the enzyme's crystal structure at high resolution, as the authors of the study report in the journal Structure.
Blue “backpacks” are found only in old termites. Photo source livescience.com
The three-dimensional structure of the enzyme showed that BP76 uses several methods of stabilization. As the researchers explain, first of all, the enzyme is tightly folded, like a sheet of paper folded many times. This helps it resist degradation over time.
In addition, there is another layer of protection provided by the sugar molecule. It attaches to the protein, resulting in the formation of a protective coating that further stabilizes the enzyme. But the most important thing is a very rare and unusually strong chemical bond between lysine and cysteine, i.e. amino acids, near the active center of the enzyme.
This type of bond is not normally found in enzymes, but in this case it plays a vital role in maintaining the structure of BP76. This bond serves as a kind of locking mechanism that ensures that the enzyme does not change shape and remains functional and fully ready to be used whenever the termite needs it to save its colony.
Old termites are not as effective for the colony, but they are useful for its protection. Photo source: spektrum.de
As the researchers explain, knowing the individual components of the device can help us understand how it works. In the same way, knowing the three-dimensional structure of a molecule helps us understand a biological process.
Why Termites Developed the Ability to Explode
The ability of kamikaze termites to accumulate a toxic substance and use it is important for colony defense. Previous studies have shown that the mandibles (upper paired jaws) of termites become dull over time. As a result, older worker termites become less effective in maintaining the nest and obtaining food. Let us remind you that young termites are extremely productive.
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But during their lives they accumulate a toxic substance and become the owners of exploding backpacks. Thus, old termites specialize in performing colony defense through a deadly act. As a result, all individuals in the colony remain extremely useful until the end of their days.