Stylet penetration behaviors of Graphocephala atropunctata (Signoret) (Hemiptera, Cicadellidae): EPG waveform characterization and quantification

Abstract

We analyzed the probing (stylet penetration) behaviors of the sharpshooter leafhopper Graphocephala atropunctata (Signoret) on grape with an alternating current (AC) electrical penetration graph (EPG) monitor. We characterized waveforms likely to represent stylet penetration pathway phase and xylem ingestion. The total probing duration of the cohort represented 68% of all 20-h monitoring periods for all insects, yet only a small proportion of that probing time was spent in high amplitude/pathway activities. Few changes in behavior occurred once a probe had started. This was shown by the low number of waveform events (i.e., uninterrupted occurrences of a behavior) per probe for each waveform type, which varied from a mean of 1-2.43. Conditional probability analysis supported that hypothesis, because insects usually terminated a probe and began a new one after ingestion-related events, rather than repeating in the same probe the previously performed waveforms. The size of grape leaves used for the assays directly influenced the amount of time insects ingested from xylem or performed other low-amplitude waveforms. Information from this work establishes benchmarks for future research addressing the mechanisms of Xylella fastidiosa Wells et al. transmission and sharpshooter ecology.