Electrically Recorded Feeding Behavior of Nephotettix cincticeps

Abstract

Feeding activities of the green rice leafhopper (GRL), Nephotettix cincticeps, on rice plants were electrically monitored with a high impedance D.C. pre-amplifier, specifically to avoid any external currents during the preparation. Behaviors of the insect were also monitored with a video camera fitted with a macro lens and honeydew excretion was recorded. When freed to choose feeding sites, GRLs fed mainly on the leaf blade although some feeding took place on the leaf sheath (80% : 20% of time spent feeding, respectively). On the leaf blade, GRLs fed mainly on the adaxial surface and their probing was distributed evenly throughout the entire surface of the leaf, veins being penetrated directly. On the leaf sheath, GRLs mainly probed on the adaxial protoderm (31%) and at the borders of vascular bundle (41%). Direct injection of a stylet into veins rarely took place and vascular bundles were approached indirectly. Microsections of leaf blades and sheaths were analyzed in order to correlate the electrical penetration graphs (EPGs) recorded with the insect's stylet probing. Waveforms corresponding to stylet probing in the epidermis and parenchyma (type S), and in the lacuna and all other areas outside the vascular bundle (type O) were identified on the leaf sheath and blade. On the leaf sheath, waveforms corresponding to probing in the xylem (type X) and phloem (type Ph) were found. On the leaf blade, where sections showed that GRLs were probing in very small vascular bundles in many cases, one pattern, corresponding to vascular bundle probing (type XP) was found and distinct patterns corresponding to stylet positions in either phloem or xylem were not found. Electrical monitoring showed that the GRLs spend most of their time probing in vascular bundles (84% blade, 81% sheath) and, on the sheath, more time is spent in the phloem bundle sheath (55%). When feeding on the leaf blade, GRLs spend 12% of their time probing in the parenchymatous tissue, although relatively less time is spent doing this on the sheath. When EPG recording was combined with monitoring honeydew excretion, an extremely high rate of excretion was discovered where xylem probing in the sheath is accompanied.