Probing Behavior of Nezara viridula on Soybean: Characterization and Comparison of Electrical Penetration Graph (EPG) Waveforms on Vegetative and Reproductive Plant Structures

Abstract

Abstract Electrical penetration graphing, or electropenetrography (EPG), is a method of indirectly visualizing stylet movement and feeding behavior of phytophagous hemipterans in plant tissue. Here we characterize the EPG waveforms of Nezara viridula (L.) (Hemiptera: Pentatomidae) feeding on soybean, using AC-applied voltage and 107 input impedance with a Backus and Bennett AC-DC monitor. Three distinct feeding-associated waveforms (i.e., waveforms within probes) were recognized for both adults and fifth instars. Pathway (Nv1) represents stylet movements through the plant from initial puncture until the target tissue is located, accompanied by secretion of saliva. An ingestion waveform (Nv2) occurred on pods, petioles, and stems; it was shown histologically on stems to correlate with stylets positioned in xylem. In contrast, Nv3 occurred only on pods and likely represents cell rupture feeding (salivation plus ingestion). We found no indication of ingestion from phloem. EPG variables (waveform attributes, probing and waveform frequencies, and durations) were compared to examine the effect of soybean developmental stage (vegetative, early pods, and pods with developing seed) on feeding behavior of fifth instars. In addition, we compared pathway and ingestion on excised soybean petioles with that on vegetative potted plants and determined the effect of providing water to adults during the pre-trial starvation period. Soybean developmental stage significantly affected nymphal feeding behavior, but the use of cuttings altered few waveform attributes or ingestion behaviors. Provision of water during the starvation period significantly reduced overall likelihood of probing, as well as frequency and duration of Nv2 on green beans.