An operating and evaluation circuit of an insect sensor is provided, which has a resistor that is dependent on insect infestation, whereby the circuit during stimulation via a transponder generates a current flow through the resistor, detects a change in the resistor as a change in voltage, and compares it with a predetermined threshold. The circuit includes a transponder-stimulated constant current source, which is connected with the resistor so that a constant voltage drops across the resistor.