New sensors could help develop bee-friendly plant protection

The growing global demand for plant-based foods makes the use of pesticides necessary to protect crops from pests and ensure crop yields. There is, however, a major drawback: the widespread use of pesticides has led to a considerable reduction in insect populations in the past. Of particular concern is the decline of wild bees, which contribute largely to pollination and are therefore essential to agricultural yields.

To solve this dilemma, scientists at the Fraunhofer Institute for Electronic Microsystems and Solid State Technologies (EMFT for short) are working on the development of new types of sensors as part of the Ökotox research project. These sensors are intended to contribute to the identification of substances “hostile to bees” from the first phases of development of new plant protection products.

“Our goal is that these sensors indicate a harmful effect on insects within a few hours and at the same time allow many substances to be tested in parallel, saving time and money,” explains Professor Joachim Wegener . Wegener heads the Fraunhofer Department “Cellular Sensor Technology”, located on the campus of the University of Regensburg (UR) and closely linked to the UR Institute for Analytical Chemistry, Chemotherapy and Biosensors.

The basic concept of the new approach is based on the use of insect cells as sensors. These cells have the typical metabolism of the respective insects and can indicate any harmful impacts when exposed to bioactive substances. “The cells are transferred to laboratory dishes equipped with microelectrodes at the bottom,” explains Wegener. In these so-called multi-electrode networks, the resistance of cells to alternating current (impedance) is determined in real time and accounts for the harmful effects on the cells.

The method could complement conventional bioanalytical tests, used to determine the toxic concentration of the isolated active ingredient. However, pesticides generally contain many additives, which are often responsible for unintended toxic effects. Using insect cell sensors, the effect of the entire mixture is tested in a single experiment. This allows the biological effects of new formulations to be quickly identified.

The cells are grown in the laboratory. They are frozen directly in the wells of the multi-electrode strips and stored at low temperature. Now the cells can then be thawed as needed and are ready for testing within minutes, even directly in the field, independent of a cell culture laboratory. This enables rapid and cost-effective preparation of large batches of sensor cells well before testing is performed.

So far, five different pesticides have been tested for acute cellular toxicity using this sensor technology. “The results show that some pesticides sold for domestic use are toxic at concentrations well below the recommended application concentration,” explains project manager Stefanie Michaelis.

To automate the application of sensor-loaded electrode arrays, the Fraunhofer EMFT research team developed a demonstration device that defrosts the cells and adds the samples. “The device allows precise dosing and eliminates any cross-contamination,” explains Christian Hochreiter, who planned and designed the prototype.

The extent to which the results obtained with insect cells reflect the influence on living insects will be the subject of further research.

In addition to detecting an acute insecticidal effect, the same sensor principle will be used to study various cellular functions (phenotypes) and will in the future allow the cells of different insect species to be studied simultaneously. “Our goal is to create a comprehensive impact profile of substances that goes beyond their pure acute toxicity on a single species,” explains Wegener.

The results are published in the journal Applied research.