Detection of Palm Lethal Yellowing Phytoplasma in the Salivary Glands of <i>Nesomyndus maculatus</i> and Asymptomatic Bismarck Palms from Madagascar

Palm lethal yellowing phytoplasmas (PLYPs) are plant pathogens that cause fatal infections in various palm species in tropical regions. The only confirmed vector of these pathogens is Haplaxius crudus Van Duzee (Hemiptera: Cixiidae), a planthopper found in the Neotropics and parts of North America. The recent identification of a new PLYP in Madagascar, ‘Candidatus Phytoplasma katsepyensis’, was the impetus for vector studies. In 2024, an expedition was launched to document planthopper diversity on palms in Madagascar where phytoplasmas had previously been observed to identify putative vectors. Insect specimens belonging to the genus Nesomyndus were collected in relatively high abundance (n = 101) and later determined to represent three species: N. australis, N. maculatus and N. madagascarensis. Additionally, five coconut palms tested positive by qPCR for phytoplasma among the sites surveyed. Among all specimens of all three species, only nine out of 61 specimens of N. maculatus were positive for phytoplasma based on qPCR and high resolution melt curve analysis (HRMA) with four of these nine specimens having detectable levels of phytoplasma in the salivary glands by digital PCR. All positive specimens were collected from a single site. The detection of the phytoplasma in the salivary glands provides strong evidence that N. maculatus is a competent vector of a phytoplasma strain affecting coconuts in Madagascar. Future efforts will determine if the other species are also capable of acquiring the phytoplasma as well as evaluate critical details of the transmission cycle.