Probing behavior of the leafhopper analyzed through DC electropenetrography and microscopy

Authors: RODDEE, JARIYA - Suranaree University Of Technology; WANGKEEREE, JUREEMART - Thammasat University; Backus, Elaine; HANBOOSONG, YUPA - Falcuty Of Science Khon Kaen University

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2023
Publication Date: 11/17/2023
Citation: Roddee, J., Wangkeeree, J., Backus, E.A., Hanboosong, Y. 2023. Probing behavior of the leafhopper analyzed through DC electropenetrography and microscopy. Journal of Insect Physiology. 151. Article 104584. https://doi.org/10.1016/j.jinsphys.2023.104584.
DOI: https://doi.org/10.1016/j.jinsphys.2023.104584

Interpretive Summary: Sugarcane white leaf (SCWL) disease is caused by an as-yet unnamed plant pathogenic phytoplasma. Phytoplasmas are potent, damaging plant pathogens reported to attack at least 99 plant species. SCWL is the most economically important disease of sugarcane in Thailand, and one of the most severe in Southeast Asia. Symptoms of SCWL include short and small leaves, leaf chlorosis, increased leaf proliferation, and shortened stem length, thus loss of cane yield. SCWL causes economic hardship because Thailand is the second-highest exporter of sugar in the world. The sugarcane industry employs more than 1.5 million people and generates about US$6 billion per year for the Thai economy. The leafhopper Yamatotettix flavovittatus is a carrier of the SCWL phytoplasma. The aim of this study was to identify and characterize the feeding behaviors of male, female, and mature nymphal Y. favovittatus on healthy sugarcane plants using DC electropenetrography, and to define the biological meanings of these waveforms using light and scanning electronic microscopy. The work identified five waveforms in two main feeding phases (pathway and phloem); thus, the leafhopper is a phloem-feeder. Mean durations per insect of both phloem ingestion (the phytoplasma-acquisition behavior) and phloem salivation (the phytoplasma-inoculation behavior) were significantly longer for female adults than nymphs. Our study thus contributes to a better understanding of the interactions between the insect carrier and SCWL phytoplasma-infected plants and will aid in developing novel disease management tactics for sugarcane.

Technical Abstract: Yamatotettix flavovittatus Matsumara is a new leafhopper vector of sugarcane white leaf (SCWL) phytoplasma that causes sugarcane chlorosis symptoms. The effects of stylet probing (or penetration) behaviors of Y. flavovittatus on sugarcane and its implication for SCWL phytoplasma transmission are yet to be studied. In this research, we used DC electropenetrography (EPG) to define waveforms produced by adult and fifth-instar nymphal Y. flavovittatus on sugarcane, and correlated them with salivary sheath termini (likely stylet tip locations) via light and scanning electron microscopy. The following six waveforms and associated activities are described: (NP) non-probing, (Yf1) stylet probing into epidermal cells, (Yf2) stylet probing through mesophyll/parenchyma, (Yf3) stylet contact with phloem and likely watery salivation, (Yf4) active ingestion of sap from phloem, probably sieve elements, and (Yf5) unknown stylet activity in multiple cell types. Study findings reveal that the Y. flavovittatus vector ingests phloem sap more frequently and for longer durations than from any other cell type, supporting that Y. flavovittatus is primarily a phloem feeder. Adult Y. flavovittatus show a longer total probing duration and produces high density of puncture holes on sugarcane leaves. Moreover, stylet probing behaviors revealed that adults typically ingest phloem sap more frequently and for longer durations than do fifth-instar nymphs, enhancing nutrition. Furthermore, we propose that adults are more likely to both acquire (during Yf4) and inoculate (during Yf3) higher amounts of phytoplasma than fifth-instar nymphs. This information on the stylet penetration behavior of leafhopper Y. flavovittatus serves as a basis for advanced studies on the transmission mechanism of SCWL phytoplasma.