A system is described for automated monitoring of pest insects in stored grain. It provides quantitative data indicative of the species of detected insects and is self-calibrating to maintain reliable operation over time across adverse environmental and biological conditions. The system uses electronic grain probes, each with a dual infrared-beam sensor head providing orthogonal views of falling insects. Sensor analog signals are analyzed by an embedded microprocessor, and extracted waveform parameters are transmitted back to a central computer. Filtering algorithms recognize and eliminate false detections due to extraneous (nonfalling) insect activities and provide an indication of species based on body size. Laboratory test data provide species identification templates and an analysis of Montana field test data acquired in aerated and nonaerated bins demonstrates the effectiveness of the filtering algorithms. The described system technology has been licensed by OPIsystems, Inc., Calgary, Alberta, Canada, and is commercially available as Insector.