Madrid, 23 years old (European press)
Having a powerful chewing apparatus makes it easy to crush tough foods and be successful in combat with opponents. The new sensor for measuring bite forces and its data-evaluating software allow us to understand how bite forces evolve. The final version has now been published in the journal Methods in Ecology and Evolution.
The scientists posted a video demonstrating the system (https://www.youtube.com/watch?v=UE7lCJ-BbPg). A praying mantis writhing a little between the toes of the world. When the insect approaches the sensor, it defends itself by biting the two metal plates that transfer pressure to a piezoelectric crystal. The crystal generates a charge-dependent voltage which is transmitted to a laptop computer through an amplifier. Curves appear on the screen, some rising sharply and reaching a plateau before regressing to zero. Sometimes the ups and downs are more flat, depending on how quickly the particular insect approaches full force when biting.
Rohr, a doctoral student at the Institute of Evolutionary Biology and Ecology at the University of Bonn: “There is scarcely any data available on how powerful an insect bite is.” With the “forceX” sensing system, the researchers want to investigate how the jaws, muscles and head shape of insects evolved to meet the challenges of their own environments. “It may not always be beneficial to be able to bite hard, because maintaining the ability to bite hard requires higher energy costs,” Rohr says. The strength of the sting can depend, for example, on the food the insect is feeding on or whether it needs its jaws to defend itself.
The team led by Prof. Dr. Alexander Planck developed existing systems for measuring bite forces.
In the measurement setup for researchers at the University of Bonn, a stereomicroscope, similar to a powerful magnifying lens, is used to detect if the examined insect’s lower jaw is in contact with the metal plates of the sensor in the correct location. The lower plate is stationary, while the upper plate transmits force to the sensor via a swing arm.
“Depending on the size and opening angle of the jaws, we use interchangeable bite plates of different sizes,” says Rohr, explaining the developments. “This allows the sensor to be tuned over a relatively wide range to meet the specific requirements of the animals.” The entire system is battery operated and therefore can be used for mobile measurements, even in the “wild”.
For biting insects, the researchers use a stand made of plastic. Animals completely disappear in the flask, only the head and mouthparts protruding from a small hole in the front stand out from them. “This allows us to better position the insects without having to hold them in our hands,” Rohr explains. Animals usually don’t need much persuasion before they bite. They are uncomfortable in an unfamiliar environment and defend themselves with defensive stings. If this instinctive behavior is not achieved, researchers stroke the insects’ heads with a thin brush. At the latest, insects close their jaws.
To publish them in Methods in Ecology and Evolution, the researchers determined the accuracy of the system: They did so by attaching different weights, ranging from grams to roughly kilograms, to the moving metal plate. A total of 1,600 iterations show that the deviation between measurements is a maximum of 2.2 percent. “This is very accurate,” Rohr says. The system can also be used to measure the strength of the claws of scorpions or crabs, for example.
Rohr and Planck built the system during their time at the University of Cologne, in part with the local precision engineering workshop. At the University of Bonn, they improved it and made accurate measurements. The study also describes the new “forceR” program, with which bite force values and bite curve shapes can be evaluated and compared.
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