Yamatotettix flavovittatus Matsumura (Hemiptera: Cicadellidae) is an insect vector of the sugarcane white leaf (SCWL) disease (Hanboonsong et al., 2002, 2006)—one of the most dangerous diseases and cause of significant sugarcane yield losses in Asian countries, especially in Thailand. The SCWL disease is caused by a phytoplasma pathogen, into the 16Sr group XI (Wang et al., 2014), which is an obligate parasite of the host cell and cannot be cultured. Photosynthesis and chlorophyll are reduced by approximately 90% in infected sugarcane plants (Rishi and Chen 1989). Moreover, diseased plants show proliferation, shortened internodes, and stunted leaves and stalks. Infected plants usually die or cannot develop sufficiently to produce millable canes or ratoon canes (Wongkeaw et al., 1997). The SCWL phytoplasma is transmitted and spread by infected cutting or one of its leafhopper vectors, Y. flavovittatus or Matsumuratettis hiroglyphicus (Matsumura) or (Hanboonsong et al., 2002, 2006).

Population dynamics of Y. flavovittatus indicates a high population during the rainy season from July to August in Thailand (Thein et al., 2012), reaching its peak in August. This corresponds to the highest prevalence of SCWL disease in sugarcane fields from August to September. Methods for controlling vector-borne illnesses primarily rely on using insecticides in propagated fields. However, using insecticides damages the environment and is not an effective means of vector control in large, commercial sugarcane fields. Moreover, the development of insecticide resistance in disease vectors reduces the effectiveness of insecticides (Sternberg, and Thomas, 2018). A reported technique for monitoring the Y. flavovittatus is the use of sticky traps and light traps to attractive the behavior of the insect vector (Thein et al., 2011). (Thein et al., 2011). Bacterial symbionts have also been identified for possible use in insect population control, including finding the secondary bacterial genus Wolbachia, an intracellular, maternally inherited bacterium. Wolbachia's population dynamics and phylogeny in the Y. flavovittatus leafhopper have been examined (Wangkeeree et al., 2020a, 2021a, 2021b). Wolbachia infection affects the life cycle and reproduction system of the Y. flavovittatus leafhopper (Wangkeeree et al., 2020b).

Traditional methods for SCWL management such as covering the crop with insect-proof screening (trap crop) and disease management through eradicating infected sugarcane plants. However, no efficient method for managing insect vectors and diseases has been developed. Host plant resistance offers a promising approach to reducing or controlling the SCWL disease. However, no reports of SCWL-resistant sugarcane varieties have been identified. Development of resistant sugarcane and other potential management techniques could be improved with better understanding of the feeding behaviors of Y. flavovittatus.

The electrical penetration graph technique or electropenetrography (both terms abbreviated EPG), which has been developed over the past 60 years, employs an electronic monitor to measure probing behavior of insects with piercing-sucking mouthparts, in real-time. EPG has been widely utilized for research on sap-sucking insects, such as studies of insect resistance to insecticides, factors influencing plant resistance to insects, insect vector feeding behavior.

Hemipteran behavior has been intensely and rigorously studied using EPG monitors since the 1960s, when McLean and Kinsey developed the first AC (alternating current) electronic monitors (AC EPG) (McLean and Kinsey, 1964). Monitors were then improved when Tjallingii employed a DC (direct current) and higher amplitude sensitivity (fixed at input resistor [Ri] 109 Ohms) and renamed electrical penetration graph (DC EPG) system (Tjallingii, 1978, Tjallingii, 1988). Backus and Bennett (1992) developed and tested the newer, AC-DC EPG, which combined the design features of both the AC and the DC monitors with tunable settings (Backus and Bennett, 2009; Rangasamy et al., 2015). Renamed electropenetrography, AC-DC EPG waveforms are comparable to DC EPG when the amplifier sensitivity is set at Ri 109 Ohms.

Together, all EPG systems have resulted in numerous studies on piercing-sucking insects, such as those exploring the effect of stylet probing and ingestion behaviors on rice plant tissue of the Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål) planthoppers (Cao et al., 2013; Ghaffer et al., 2011; Seo et al., 2009; Kang et al., 2022). Also, the feeding behaviors of M. persicae aphid feeding on Capsicum annuum (pepper) (Jacobson and Kennedy, 2013) were studied, as were Diaphorina citri Kuwayama psyllid (Bonani et al, 2010); pear psyllids (Civolani et al., 2011); aphids (Tjallingii, 1985); Graphocephala atropunctata (Signoret) sharpshooter leafhopper (Backus and Bennett, 1992; Joost, et al., 2006; Miranda and Fereres, 2009), and the like. Correlations have been studied between waveforms and stylet activities of the glassy-winged sharpshooter, Homalodisca coagulata (Say) (now H. vitripennis (Germar)) (Joost et al., 2006; Dugravot et al., 2008); Graminella nigrifrons (Forbes) (Triplehorn et al., 1984) and other leafhoppers (Bonani et al., 2010; Fereres and Moreno, 2009; Gerstenbrand et al., 2020; Jin et al., 2012; Miranda et al., 2009; Roddee et al., 2021; Stafford and Walker, 2009; Trebicki et al., 2012); whiteflies (Fereres and Moreno, 2009; Walker and Janssen, 2000); crapemyrtle bark scale (Wu et al., 2022); and thrips (Joost and Riley, 2005; Kindt et al., 2006).

EPG has also been used to localize plant resistance factors of aphids (Montllor and Tjallingii, 1989); Aphis craccivora Koch (Annan et al., 2000); Myzus pericae (Sulzer) (Alvarez et al., 2006); soybean aphid (Crompton and Ode, 2010; Diaz-Montana et al., 2007); apple aphid (Marchetti et al., 2009); and green rice leafhopper (Kwon et al., 2021). Effects of insecticides on probing behaviors have also been studied, such as phymetrozine (He et al., 2011), imidaclopid (Butler et al., 2012; Garzo et al., 2015), and monotypes of pyrifluquinazon (Civolani et al., 2013; Kang et al., 2012); cyantraniliprole on the probing behavior of the potato psyllid (Mustafa et al., 2015).

Plant pathogen transmission mechanisms have also been a focus of EPG studies, such as G. atropunctata sharpshooter leafhopper transmission of the Pierce’s disease bacterium, Xylella fastidiosa Wells et al. (Almeida and Backus, 2004, Roddee et al., 2021); Matsumuratettix hiroglyphicus (Matsumura) leafhopper transmission of SCWL (Roddee et al., 2017; 2019); potato psyllid Bactericera cockerelli (Šulc) transmission of Ca. Liberibacter solanaceaum, potato zebra chip bacterium (Zack et al., 2015), and D. citri psyllid transmission of Ca. Liberibacter asiaticus (Wu et al., 2016). However, the EPG technique is yet to be applied to study probing behavior of Y. flavovittatus.

The objectives of this study were to (1) study the EPG waveforms and their characteristics produced by adult and nymph Y. flavovittatus leafhopper vectors, (2) investigate the correlation between these waveforms and stylet probing behaviors using histological evidence, and (3) compare the stylet penetration of adult and nymph Y. flavovittatus leafhopper vectors using a scanning electron microscope (SEM). The study’s results provide information on probing behaviors of the Y. flavovittatus vector, which can be utilized in further studies on the localization of sugarcane resistance in different varieties.