Targeting the teeth of beetles and the like: what the mouthparts of arthropods can do can now be recorded using a clever sensor system that two German researchers have developed. The scientists explain that the values measured with the apparatus can shed light on the question of how the biting forces of small animals have developed depending on their respective lifestyle.
They serve to crush food, can be used to transport objects and used as defensive or offensive weapons: the mandible pincers fulfill important functions for the many different representatives of the arthropods. Some species are known to be able to give us a painful “trick” or even pierce our skin with their mandibles. However, little research has been done on the forces that the mouthparts of the arthropods can actually produce, report Peter Rühr and Alexander Blanke from the Rheinische Friedrich-Wilhelms-Universität Bonn.
As the two scientists emphasize, this is an interesting basic research question with implications for evolutionary biology. Because the respective bite force reflects the characteristics of species in a special way. As is so often the case in nature, the principle applied during development: the investment had to be worthwhile, explains Rühr: “It is not advantageous for every insect to be able to bite hard, since high biting forces are also associated with higher energetic costs for the animal”. , according to the scientist. Information about bite force can therefore shed light on how and why arthropods evolved specific jaw structures, muscles, and head shapes and how this relates to their lifestyles. According to Rühr and Blanke, however, the research area has so far lacked a standardized method for measuring biting force that would allow scientific data to be compared.
Bite force recorded with piezo crystals
In order to change this, the two have now developed the mobile system “forceX” in the precision mechanics workshop of the University of Cologne. The central element of the system is formed by two small metal plates, the distance between which can be adjusted to the dimensions of the animal’s jaws, the researchers explain. Beetles, praying mantises and the like are then brought to these leaflets in the focus of a magnifying binocular until they can grip them with their mandibles. In order to defend themselves, the stressed animals then usually bite violently. If this instinctive behavior does not occur, the scientists stroke their heads with a paintbrush – at the latest then the insects close their jaws and bite into the two plates, the Stirring and Blanke report.
The lower piece remains immobile, while the upper piece transmits the force to a so-called piezoelectric crystal via a seesaw. Depending on the force, this element creates a voltage that is transmitted to a laptop. Specially designed software then converts this data into values that are displayed graphically. In this way, forceX enables detailed information about the course and maximum severity of the bite of insects and other arthropods, the scientists report.
Video: A praying mantis bites into the measuring plates. © Peter/ University of Bonn
From tiny teethers to massive versions
“Depending on the size and opening angle of the jaws, we use bite plates of different sizes, which can be exchanged,” explains Rühr. “This means that the sensor can be adapted to the respective requirements of the animals over a relatively large span”. The entire system is battery-operated and can therefore be used for measurements on the move – so it can also be used in field research without any problems, the researchers emphasize. The researchers also have a solution for dealing with animal subjects who defend themselves with other weapons in addition to their mandibles: they use a plastic holder for stinging species. Only the head with the mouthparts protrudes from this sleeve through a small hole. “This allows us to better position the animals without having to hold them in our hands,” says Rühr.
The two researchers are now making the concept of their sensor system available to the scientific community: “Our bite force sensor system is intended to provide a basis for replicas,” says Rühr. According to him, essential parts of the apparatus can also be easily produced with a 3D printer. Stir and Blanke hope that their concept can contribute to expanding the previously poor knowledge about closing forces in arthropods. Finally, they again emphasize the adaptability of their system: In addition to examining the diverse versions of jaw tools in insects, the system could also illustrate the power of scissors: You could also have scorpions and crabs pinched in forceX, say the scientists.
Source: University of Bonn, specialist article: Methods in Ecology and Evolution, doi: 10.1111/2041-210X.13909