Lygus lineolaris (Palisot de Beauvois) and Lygus hesperus Knight are among the most important pests affecting production of cotton in the United States. Lygus spp. use a cell rupture feeding strategy. However, the precise stylet-probing behaviors of adult Lygus spp. are not well understood or quantifiably related to cotton damage. The long-term goals of our research are to: 1) relate stylet probing to damage, and 2) quantitatively compare L. lineolaris feeding among resistant and susceptible host plants. The specific objectives of this study were to apply the latest technology in electropenetrography (EPG) to record adult, prereproductive Lygus spp. feeding, to identify and characterize all the waveforms, and to hypothesize their biological meanings. We used a third-generation AC-DC electropenetrograph to record nonprobing and probing waveforms of adult bugs on pinhead (<3mm) cotton squares, and constructed a waveform library from the output. Recordings were obtained with both AC and DC applied signals and at different input impedances (10(6)-10(9) Omega). Three nonprobing waveforms were identified and visually correlated: Standing still (S), walking (W), and antennation (A). Probing waveforms were classified as: cell rupturing (CR), transition (T), and ingestion (I). T waveform is the first finding of an X wave for a nonsalivary sheath feeder in Hemiptera, implying that tasting/testing/acceptance behaviors can be performed by a cell rupture feeder. While waveform I is not performed in every probe, when performed, its appearance and structure were affected by applied signal and input impedance. Overall, time spent in nonprobing behaviors was longer than time spent on probing behaviors.