Characterization of an EPG Waveform Library for Redbanded Stink Bug, Piezodorus guildinii (Hemiptera: Pentatomidae), on Soybean Plants
Feeding behaviors of the redbanded stink bug, Piezodorus guildinii (Westwood), on vegetative (stem and leaflet) and reproductive (pod) tissues of soybean, Glycine max (L.), were recorded using an AC-DC electropenetrograph (EPG) apparatus. Eight different probing waveforms were characterized and defined: Pg1a, Pg1b, Pg1c, Pg1d, Pg2, Pg3a, Pg3b, and Pg4 grouped into three different families, P, I, and N. Histological studies of intact stylets within salivary sheaths observed during Pg1b, Pg1c, Pg2, and Pg3 waveforms were correlated with the specific penetration sites. Waveforms Pg1a, Pg1b, Pg1c, and Pg1d (pathway-family P) occurred at the start of probing activities and represent stylet penetration deep into plant tissue. Waveforms Pg2, Pg3a, and Pg3b (family I) represent the food ingestion phase. Pg2 waveform represents xylem sap ingestion primarily on leaves and stems. During Pg3a, stylets were moving, lacerating deeply into pod tissue and partially retracting; during Pg3b, stylets were motionless inside the pod tissue. Pg3b occurred interspersed with waveform Pg3a. Waveform Pg4 (family N) represented short interruptions that occurred within waveform Pg2. The study demonstrated that P. guildinii uses the cell rupture strategy to ingest from endosperm in soybean pod, and the same insect could switch to salivary sheath feeding to ingest from xylem in soybean leaves and stems. This unusual behavior explains symptoms of stink bug damage to soybean. The P. guildinii waveforms defined herein will allow future EPG studies to aid in development of soybean varieties that resist the feeding and damage caused by this and other stink bug pests.