Characterization of electrical penetration graphs of Bucephalogonia xanthophis, a vector of Xylella fastidiosa in citrus

Abstract

The sharpshooter Bucephalogonia xanthophis (Berg) (Homoptera: Cicadellidae) is a vector of the xylemlimited bacterium, Xylella fastidiosa (Wells, Raju, Hung, Weisburg, Mandelco-Paul, and Brenner), which causes citrus variegated chlorosis. Despite the importance of citrus variegated chlorosis, the probing behavior of vectors on citrus and its implications for transmission of X. fastidiosa have not been studied. Here we studied electrical penetration graph (EPG-DC system) waveforms produced by B. xanthophis on Citrus sinensis (L.) Osbeck (Rutaceae), and their relationships with stylet activities and xylem ingestion. Electrical penetration graph waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration on plant tissues. The main waveforms were correlated with histological observations of salivary sheaths in plant tissues and excretion analysis, in order to determine stylet activities and their precise position. Six waveforms and associated activities are described: (S) secretion of salivary sheath and intracellular stylet pathway, (R) resting during stylet pathway, (Xc) contact of stylets with xylem vessels, (Xi) active xylem ingestion, (N) interruption within the xylem phase (during Xc or Xi), and (W) withdrawal of stylet from the plant. The sharpshooter spent 91.8% of its probing time with its stylet in the xylem, where the main activity was ingestion (Xi: 97.5%). During a probe, the most likely sequence of events is secretion of salivary sheath and pathway (S) through epidermal and parenchyma cells (all individuals), followed by contact with xylem (Xc) (67.6% of all individuals) and ingestion (Xi) (88.3% of those that exhibit waveform Xc). The mean time to contact the xylem (Xc) and initiate ingestion (Xi) after onset of the first probe was 27.8 and 34.2 min, respectively. However, sustained xylem ingestion (Xi > 5 min) was established after 39.8 min, on average. This information is basic for future studies on the transmission mechanisms of X. fastidiosa and in order to establish control strategies aimed at interfering with this process.

Characterization of EPG waveforms for the tea green leafhopper, Empoasca vitis Göthe (Hemiptera: Cicadellidae), on tea plants and their correlation with stylet activities

“…The waveforms recorded in our artificial diet experiment were nearly identical in appearance to the above waveforms. In active ingestion, the waveforms, whether correlated with stylet tips in xylem or mesophyll, are all characterized by a highly stereotypical pattern at a constant repetition rate of about 4-6 Hz (Lett et al, 2001;Dugravot et al, 2008;Miranda and Fereres, 2009;Stafford and Walker, 2009;Seo et al, 2009;Bonani et al, 2010;Civolani et al, 2011).…”

Sharpshooter X Wave: Correlation of an Electrical Penetration Graph Waveform with Xylem Penetration Supports a Hypothesized Mechanism forXylella fastidiosaInoculation

“…Although sharpshooter pathway activities are intracellular, the presumed tightness of the salivary sheath seal into a xylem cell (to prevent cavitation, see below) may allow similar charge separation to be sustained during ingestion, indicating extracellular stylet tip position in xylem (Miranda et al 2009). If so, then researchers could consistently use C1 occurring at a positive voltage level to deÞnitively ascertain xylem penetration during pathway, as is proposed in the study of Brazilian sharpshooters by Miranda et al (2009). It is therefore provocative that C1 even during pathway XN is often positive in our study, supporting that xylem is Þrst penetrated during partial XN, not as late as XC.…”

“…When sharpshooters are recorded at input impedance 10 6 ohms, all signals are positive (Backus et al 2005). At 10 9 ohms, a majority of signals are negative-then-positive (Miranda et al 2009). At the present 10 8 ohms, the best-wired insects often showed both negative and positive voltage levels.…”

Probing behavior of Dysmicoccus brevipes mealybug in pineapple plants1

“…This technique has been previously used to study the probing behavior of several sucking insects (Calatayud et al 1994, Kindt et al 2006, Miranda et al 2009, Cid & Fereres 2010, Lazzarotto et al 2011, Liu et al 2013, Moraes et al 2013, Santa-Cecília et al 2013, plant resistance (Crompton & Ode 2010) and viral transmission (Tjallingii & Prado 2001, Fereres & Moreno 2009). …”