Research with Bite | Mirage News

Press release from the University of Bonn.

Scientists from the University of Bonn present a sensor system capable of measuring the bite force of insects.

A praying mantis (Hierodula sp.) bites into the sensor plates. Credit: Volker Lannert, University of Bonn.

How badly can insects bite? Having a powerful chewing device makes it easier to crush harder foods and successfully fight fights with enemies. Biologists from the University of Bonn are now presenting a mobile system (forceX) for measuring the bite forces of small animals, as well as the forceR software for evaluating the data. This allows researchers to understand how biting forces evolved. The final version is now published in the journal Methods in ecology and evolution with funding from the European Research Council and the German Research Foundation.

The praying mantis squirms a little in the scientist’s hand. When the insect approaches the sensor, it defends itself by biting the two metal plates which transfer pressure to a piezo crystal. The crystal generates a load-dependent voltage which is transmitted to a laptop through an amplifier. Curves appear on the screen, some of which soar and tremulously reach a plateau before falling back to zero. Sometimes the ascent and descent are flatter – depending on how fast the insect approaches maximum force when biting.

Virtually no data on bite force

“There are hardly any data available on the bite force of insects, says Peter T. Rühr, PhD student at the Institute for Evolutionary Biology and Ecology at the University of Bonn. With their “forceX” sensor system, the researchers want to study how the mandibles, musculature and head shape of insects have evolved to meet the challenges of their respective environments. “It is not always advantageous to be able to bite hard, because maintaining this ability requires higher energy costs,” says Rühr. The bite force may depend, for example, on what food an insect feeds on or whether it needs the mandibles for self-defence.

“Maintaining the ability to bite hard requires higher energy costs”

The team led by Professor Dr. Alexander Blanke, who obtained a European Research Council (ERC) start-up grant, developed the existing systems for measuring bite forces.

Researchers at the University of Bonn used a stereomicroscope, similar to a powerful magnifying glass, to detect whether the mandibles of the insect under study are in contact with the metal plates of the sensor in the right place. The lower platen is stationary, while the upper platen transmits the force to the sensor via a rocker.

Suitable for studying the bite forces of many different small animals

“Depending on the size and opening angle of the mandibles, we use interchangeable bite plates of different sizes,” says Rühr, explaining the progress. “This allows the sensor to be adjusted over a relatively wide range to meet the particular needs of the animals.” The complete system is battery-powered and can therefore be used for mobile measurements – even in the wild.

The bite curves of a praying mantis (Hierodula sp.) measured by the forceX system can be viewed on a laptop computer.  In the background, Peter T. Rühr performs the measurement.
The researchers’ forceX system, which measures each insect’s bite curves, is compact enough to take anywhere. Credit: Volker Lannert, University of Bonn.

For the biting insects, the researchers use a plastic “support”. The animals disappear completely into the flask, with only its head and mouthparts protruding from a small hole in the front. Rühr: “This allows us to better position the insects without having to hold them in our hands. Usually animals don’t need much persuasion before biting. They feel uncomfortable in an unfamiliar environment and defend themselves with their defensive bites. If this instinctive behavior doesn’t materialize, the researchers stroke the insects’ heads with a delicate brush – prompting the insects to close their jaws.

Highly accurate measurements for bite force

For publication in Methods in Ecology and Evolution, the researchers determined the accuracy of the system: They did so by attaching different weights, ranging from one gram to nearly one kilogram, to the moving metal plate. A total of 1600 repetitions shows that the deviation between the measurements is at most 2.2%. “It’s very precise,” says Rühr. The system can also be used to measure the strength of scorpion or crab claws, for example.

Rühr and Blanke built the system while at the University of Cologne, partly with the local precision engineering workshop. At the University of Bonn, they further optimized it and carried out the precision measurements. The manuscript also describes the new “forceR” software, with which bite force values ​​and shapes of bite curves can be evaluated and compared. The researchers do not want to commercialize the bite force sensor system. “On the contrary, the results presented in ‘Methods in Ecology and Evolution’ provide the basis for the repetitions,” says Rühr. The essential parts of the sensor can even be reproduced using a 3D printer.

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