|GODFREY, LAWRENCE - UNIVERSITY OF CALIFORNIA|
|AKBAR, WASEEM - MONSANTO CORPORATION|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2016
Publication Date: 6/21/2016
Citation: Backus, E.A., Cervantes, F.A., Godfrey, L., Akbar, W. 2016. Characterization of an EPG waveform library for pre-reproductive adult Lygus lineolaris and L. hesperus feeding on cotton squares. Annals of the Entomological Society of America. 109:684-697.
Interpretive Summary: Tarnished plant bugs, Lygus lineolaris and L. hesperus, are among the most important pests affecting production of cotton in the mid-southern and western United States. Developing cotton squares (floral buds) are damaged by wounding and saliva secreted during feeding. Varieties of cotton resistant to plant bug feeding must be developed, but the present inability to directly observe and measure such feeding in relation to damage hampers development. The best way to alleviate this problem is to use electropenetrography (EPG) to record plant bug feeding. Studies were conducted using AC-DC EPG to record tarnished plant bug feeding behaviors on pinhead-sized (<3 mm) cotton squares. Three different non-feeding waveforms (representing walking, standing still, and antennal tapping) were characterized and biologically defined by visual observation. In addition, three feeding waveforms were characterized; biological meanings were hypothesized based on electrical characteristics of the waveforms. These waveforms were CR (representing stylet movements/salivation), T (representing tasting and acceptance), and I (representing swallowing of liquefied plant cell contents). These new definitions of plant bug waveforms will allow future EPG studies to aid in development of cotton varieties that resist the feeding and damage caused by this insect pest.
Technical Abstract: Tarnished plant bugs, Lygus lineolaris and L. hesperus, are among the most important pests affecting production of cotton in the mid-southern and western United States, respectively. Previous studies have focused on feeding damage to cotton reproductive structures from destructive enzymatic saliva. Nonetheless, precise stylet probing behaviors of adult Lygus spp. are not well understood or quantifiably related to cotton damage. The goal of this study was to begin to apply the latest technology in electropenetrography (EPG) to rigorously understand Lygus spp. feeding. A 3rd-generation, AC-DC electropenetrograph was used to record non-probing and probing waveforms of adult, pre-reproductive Lygus spp. on pinhead (<3 mm) cotton squares. Waveforms were identified and characterized to construct a waveform library for Lygus spp.; biological meanings of waveforms were inferred based on electrical orgins. Recordings were obtained with both AC and DC applied signals and at different input impedances (10^6–10^9 Ohms). Three non-probing waveforms were identified and visually correlated: Standing still (S), walking (W), and antennation (A). Probing waveforms were classified within three families: cell rupturing (CR), transition (T), and ingestion (I). CR waveform is typically observed at the beginning of every new probe and always starts with a large change in voltage, either positively or negatively oriented based on the applied signal and input impedance. T waveform comprises two or three types (T1, T2, and/or T3; depending on species) that are clearly differentiated with both AC and DC applied signal at 10^8 or 10^9 Ohms. This T waveform is the first finding of an X wave for a non-salivary sheath feeder in Hemiptera, implying that acceptance behaviors can be performed by a putative cell rupture feeder. While waveform I is not performed in every probe when performed, waveform I appearance and structure is affected by applied signal and input impedance. These new definitions of Lygus spp. EPG waveforms will allow future EPG studies to aid in development of cotton varieties that are resistant to plant bug feeding and damage.