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A poly3-hexylthiophene (P3HT) thin-film sensor was designed, fabricated and tested to detect volatile compounds secreted by plants when attacked by insects. The sensor is inexpensive and small enough to be easily attached to plants. The sensor can be used for early onsite detection of insect infestation. The chemical resistor sensor consists of micro-electronically fabricated interdigitated electrodes, coated with a P3HT thin film that was deposited by spin coating. The sensor's doping profile; annealing profile and thickness were optimized for detecting γ-terpinene a chemical emitted by pine trees during bark beetle infestation. The vapors of γ-terpinene interacted with the optimized P3HT film causing an increase in the resistance of the sensor by more than two orders of magnitude at room temperature. The detection limit was found to be 36 ppm, which is sufficient for detecting insect infestations.