How Hard Can Insects Bite? New System Allows Scientists To Obtain Previously Unknown Data



University of Bonn researchers have created an insect biting force sensor device.

How ferociously can a bug bite? Strong chewing muscles make it easier to successfully break down more difficult food and destroy enemies. The forceX mobile equipment and forceR software were created by the biology department at the University of Bonn to measure the biting forces of small animals. This enables us to understand how biting forces, like those of insects, have evolved. In the journal Methods in Ecology and Evolution, the findings were just just published.

In the scientist's palm, a praying mantis wriggles a little. As it approaches the sensor, the insect defends itself by biting down on the two metal plates that send pressure to a piezo crystal. The voltage generated by the crystal, which is load-dependent, is transmitted to a laptop using an amplifier. There are numerous curves visible on the screen, some of which jerkily ascend abruptly, reach a plateau, and then revert to zero. The rise and fall may occasionally be flatter depending on how quickly an insect reaches the maximum force at which it may bite.

Praying Mantis that Bite Curves

Praying mantis biting patterns as determined by the forceX system and displayed on the laptop. Peter T. Rühr is conducting the measurement in the backdrop. Credit: University of Bonn/Volker Lannert

There are few studies on bite force.

According to Peter T. Rühr, a doctorate candidate at the University of Bonn's Institute of Evolutionary Biology and Ecology, "There is hardly any evidence available on how hard insects can bite." To better understand how insects' mandibles, musculature, and head shapes have changed to adapt to their distinct surroundings, researchers are using their sensor system "forceX." The capacity to bite forcefully may not always be advantageous because it requires more energy to sustain, according to Rühr. The biting force may vary depending on the type of food an insect consumes or whether it needs to defend itself with its mandibles.

Bug Light Traps

Insects are captured in the dark using a light trap, and their biting force is then determined. Image credit: Peter T. Rühr/Bonn University

The group expanded upon the mechanisms already in place for monitoring biting forces under the leadership of Professor Dr. Alexander Blanke, who has been given a Starting Grant by the European Research Council (ERC).

The researchers from the University of Bonn used a stereo microscope, which is equivalent to a strong magnifying glass, to check whether the mandibles of the insect under investigation are in contact with the metal plates of the sensor at the appropriate area. While the bottom plate is immobile, the top plate uses a rocker to send the force to the sensor.

It is possible to adapt the size of the mandible.

Rühr explains the improvements by saying, "We employ different sized, interchangeable bite plates depending on the size and opening angle of the mandibles." This enables the sensor to be set over a sizable range to accommodate the specific needs of the animals. Because the entire system runs on batteries, it may be used for mobile measurements anywhere, even in the "wild."

Stump Bug Biting A stag beetle (Lucanidae sp.) that bit the sensor's metal plates. Image credit: Peter T. Rühr/Bonn University

The researchers employ a plastic holder for stinging insects. Only the head with its mouthparts poking out of a tiny hole at the front remains of the animals after they entirely vanish inside the vial. Rühr: "We can now place the insects more effectively without needing to hold them in our hands." Typically, the animals don't require much convincing before biting. In the strange setting, they become uneasy and defend themselves by biting. If the researchers rub the insect heads with a soft brush, the insects will eventually close their mouths if this instinctual behavior does not occur.

high degree of measuring accuracy

The researchers tested the system's precision before publishing their findings in Methods in Ecology and Evolution. They did this by fastening various weights, ranging from one gram to nearly one kilogram, to the movable metal plate. A total of 1,600 trials indicate that the largest difference between values is 2.2 percent. Rühr adds, "That's extremely accurate." The technique can also be used to gauge the strength of, say, a crab's or a scorpion's claws.

System for Mobile ForceX

The transportable forceX system is easy to store in a car's trunk. Batteries that can be recharged provide the power. Image credit: Peter T. Rühr/Bonn University

During their stay at the University of Cologne, Rühr and Blanke partially used the neighborhood precision engineering workshop to build the system. They enhanced it and carried out the accuracy tests at the University of Bonn. The book also describes the new "forceR" program, which allows users to assess and contrast bite force values and bite curve forms. The researchers are not interested in commercializing their bite force sensor technology. Instead, Rühr claims that the findings in "Methods in Ecology and Evolution" serve as the foundation for replications. Even with a 3D printer, key sensor components can be duplicated.

Reference: Peter T. Rühr and Alexander Blanke, "forceX and forceR: A mobile setup and r package to measure and analyze a wide range of animal closing forces," Methods in Ecology and Evolution, 29 May 2022.

The European Research Council (ERC) and the German Research Foundation provided funding for the study (DFG).

By UNIVERSITY OF BONN 

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