Electrical penetration graphic waveforms in relation to the actual positions of the stylet tips of Nilaparvata lugens in rice tissue

The stylet penetration behavior of Nilaparvata lugens (Hemiptera: Delphacidae) in rice plants (Oryza sativa) was evaluated through the use of an electrical penetration graph (EPG). To accomplish this, we classified the EPG signals into seven different waveforms, np, N1, N2, N3, N4-a, N4-b, and N5, according to their shapes, amplitudes, and frequencies. The N4-b waveform was always preceded by N3 and N4-a, in that order. Continuous honeydew excretion only occurred during the N4-b period, and the honeydew deposited on a filter paper containing ninhydrin reagent during the N4-b period was stained violet. The tips of the stylets that were severed in the N3, N4-a, and N4-b periods were in the phloem region of rice. Moreover, the flow of plant sap after stylectomy only occurred during the N4-b period. Finally, sucrose was the only carbohydrate component identified when HPLC analysis of the plant sap was conducted. On the other hand, honeydew excretion hardly occurred during the N5 period and the tips of the stylets that were severed during the N5 period were located in the xylem region of rice. Based on the location of the stylets and honeydew excretion, the EPG waveforms for the stylet penetration behaviors of N. lugens were assigned to the following groups; np: non-penetration of stylets, N1: penetration initiation, N2: salivation and stylet movement, N3: an extracellular activity near the phloem region, N4-a: an intracellular activity in phloem region, N4-b: phloem sap ingestion, and N5: activity in the xylem region.