Transmission of Xanthomonas albilineans by the spittlebug, Mahanarva fimbriolata (Hemiptera: Cercopidae), in Brazil: first report of an insect vector for the causal agent of sugarcane leaf scald.

Leaf scald is a destructive sugarcane disease caused by the bacterium Xanthomonas albilineans (Ashby) Dowson. This pathogen presents the gene cluster SPI-1 T3SS, a conserved feature in pathogens vectored by animals. In this study, the competence of Mahanarva fimbriolata (Stål), a spittlebug commonly found in sugarcane fields in Brazil, was evaluated for the transmission of X. albilineans. Artificial probing assays were conducted to investigate the ability of M. fimbriolata adults to acquire X. albilineans from artificial diets containing the pathogen with subsequent inoculation of X. albilineans into pathogen-free diets. Plant probing assays with M. fimbriolata adults were conducted to evaluate the acquisition of X. albilineans from diseased source plants and subsequent inoculation of healthy recipient sugarcane plants. The presence of X. albilineans DNA in saliva/diet mixtures of the artificial probing assays and both insects and plants of the plant probing assays were checked using TaqMan assays. The artificial probing assays showed that M. fimbriolata adults were able to acquire and inoculate X. albilineans in diets. Plant probing assays confirmed the competence of M. fimbriolata to transmit X. albilineans to sugarcane. Over the entire experiment, 42% of the insects had acquired the pathogen and successful inoculation of the pathogen occurred in 18% of the recipient-susceptible sugarcane plants at 72 or 96 h of inoculation access period. Assays evidenced the vector competence of M. fimbriolata for transmission of X. albilineans, opening new pathways for investigating the biology and the economic impacts of the interaction between X. albilineans and M. fimbriolata.