Waveform characterization of the soybean stem feeder Edessa meditabunda (F.) (Hemiptera: Heteroptera: Pentatomidae): overcoming the challenge of wiring pentatomids for EPG

Stink bugs (Pentatomidae) are in general robust and restless insects, which makes them difficult to wire for electropenetrography (EPG) studies. In addition, cuticular lipids may reduce wire effectiveness and their removal could improve success of wiring. We compared wiring effectiveness for three species of stink bugs, each with different movement behaviours and degrees of cuticular waxiness, i.e., Piezodorus guildinii (Westwood), Nezara viridula (L.), and Loxa deducta (Walker). Results indicated that removal of cuticular lipids by mechanical abrasion (via sanding) greatly improved attachment success with gold wire. However, our hypothesis that heavier and bigger bugs would lose the wire attachment more quickly compared with lighter and smaller bugs was not confirmed, for either sanded or unsanded bugs.  In contrast, our hypothesis that greater activity and movement on the part of a bug species would cause the wire to break more often was supported by extensive testing.   Behavior seems to be an important trait, more relevant for successful wiring than body weight. We used that technique to characterize and correlate DC EPG waveforms for the large and restless, stem-feeding stink bug, Edessa meditabunda (F.) on soybean plants.  This marks the first published example of pentatomid EPG waveforms. E. meditabunda recordings on soybean stems generated eight types of waveforms in three phases and two families, named: non-probing = Np and Z; pathway phase = Em1; X wave phase = X; ingestion phase, family I = Em2 and Em3; ingestion phase, family N = Em4 and Em5.  These eight were described based on their frequencies, relative amplitudes, and level voltages. Histological studies of stylets within salivary sheaths correlated the Em1, Em2, and Em3 waveforms with the specific penetration sites. The waveform with the longest duration during feeding was Em2, representing xylem sap ingestion; in addition, waveform Em3 (always preceded by an X wave) was correlated with phloem sap ingestion.