Tiny beetle’s explosive spray mechanism revealed by X-rays
Many
beetles secrete foulsmelling or bad-tasting chemicals from their
abdomens to ward off predators, but bombardier beetles take it a step
further. When threatened, they combine chemicals in an explosive
chemical reaction chamber in their abdomen to simultaneously synthesise,
heat and propel their defensive load as a boiling hot spray, complete
with "gun smoke." They can even precisely aim the nozzle at the
attacker.
Wendy Moore, an assistant professor in the Department of Entomology at the University of Arizona, just published a paper together with a multidisciplinary team of scientists that not only reveals the beetle's firing apparatus in never-before-seen detail, but also solves a long-standing mystery of how the animals achieve their insane rapid-fire capabilities.
"Understanding how these beetles produce - and survive - repetitive explosions could provide new design principles for technologies such as blast mitigation and propulsion," said the lead authors of the study about the motivation for their research.
The study was led by Eric Arndt and Christine Ortiz from the Massachusetts Institute of Technology.
Using enzymes that digest away muscle and fat, Moore could clean the reaction chamber and examine it with optical microscopy in detail. While studying the shape of the reaction chamber, she noticed that some regions of the chamber wall were thin and not as strong as others, and that one region near the mixing valve looked particularly thin. She predicted that this thin cuticle would be displaced by the force of the reactions in such a way that it would impinge upon the valve, temporarily shutting off the flow of reactants. To investigate this hypothesis, the team decided to directly observe the internal dynamics of spray pulsation in live beetles.
The team took hundreds of the species Brachinus elongatulus beetles to co-author Wah-Keat Lee, he helped set up an experiment to obtain X-ray video of beetles firing their smoking rounds at up to 2,000 frames per second. They team set up the beetles in a tightly sealed room next to the synchrotron - a particle accelerator that can produce intense X-rays.
The researchers observed how the beetles regulate the ultrafast micropulses, something that had never been achieved before. It turns out the pulses are generated in a passive way, not through an active process involving muscle contraction, as had been hypothesised before. As the chemicals pass through a valve into the reaction chamber, they mix with enzymes and explosively liberate oxygen gas, water vapor and heat, propelling a hot, noxious spray down the nozzle and out the exit pore. Each explosion inside the chamber forces a highly elastic region of the chamber wall to expand and impinge on the valve that separates the two chambers, temporarily cutting off the flow of reactants and resulting in a pulsed delivery.
While it is still not completely clear why it might be beneficial to the beetle to have a pulsed delivery, Moore suspects that dividing the spray into very short, rapid pulses allows the beetle to sustain the energy of the blast and its small body size at the same time. MM
Wendy Moore, an assistant professor in the Department of Entomology at the University of Arizona, just published a paper together with a multidisciplinary team of scientists that not only reveals the beetle's firing apparatus in never-before-seen detail, but also solves a long-standing mystery of how the animals achieve their insane rapid-fire capabilities.
"Understanding how these beetles produce - and survive - repetitive explosions could provide new design principles for technologies such as blast mitigation and propulsion," said the lead authors of the study about the motivation for their research.
The study was led by Eric Arndt and Christine Ortiz from the Massachusetts Institute of Technology.
Using enzymes that digest away muscle and fat, Moore could clean the reaction chamber and examine it with optical microscopy in detail. While studying the shape of the reaction chamber, she noticed that some regions of the chamber wall were thin and not as strong as others, and that one region near the mixing valve looked particularly thin. She predicted that this thin cuticle would be displaced by the force of the reactions in such a way that it would impinge upon the valve, temporarily shutting off the flow of reactants. To investigate this hypothesis, the team decided to directly observe the internal dynamics of spray pulsation in live beetles.
The team took hundreds of the species Brachinus elongatulus beetles to co-author Wah-Keat Lee, he helped set up an experiment to obtain X-ray video of beetles firing their smoking rounds at up to 2,000 frames per second. They team set up the beetles in a tightly sealed room next to the synchrotron - a particle accelerator that can produce intense X-rays.
The researchers observed how the beetles regulate the ultrafast micropulses, something that had never been achieved before. It turns out the pulses are generated in a passive way, not through an active process involving muscle contraction, as had been hypothesised before. As the chemicals pass through a valve into the reaction chamber, they mix with enzymes and explosively liberate oxygen gas, water vapor and heat, propelling a hot, noxious spray down the nozzle and out the exit pore. Each explosion inside the chamber forces a highly elastic region of the chamber wall to expand and impinge on the valve that separates the two chambers, temporarily cutting off the flow of reactants and resulting in a pulsed delivery.
While it is still not completely clear why it might be beneficial to the beetle to have a pulsed delivery, Moore suspects that dividing the spray into very short, rapid pulses allows the beetle to sustain the energy of the blast and its small body size at the same time. MM
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