Macropsis mendax (Homoptera: Cicadellidae) is a vector of Phytoplasma ulmi in Italy
Elm yellows was first observed in the eastern part of USA where it caused a severe decline in native American elms (Ulmus americana and other species). The disease was first called ‘phloem necrosis’ and later associated with the presence of phytoplasmas (Elm phloem necrosis phytoplasma is currently on the EPPO A1 list*). Following the first descriptions of the disease, elm yellows was thought to be restricted to North America. In USA, the only confirmed vector is Scaphoideus luteolus (Homoptera: Cicadellidae) which does not occur in Europe. Other species like Philaenus spumarius (Homoptera: Cercopidae) and Allygidius atomarius (Homoptera: Cicadellidae) have been suggested as possible vectors. Since the 1950s, the disease has been reported from Italy, Czechia, France and Germany. In Italy, it was found in Emilia-Romagna, Toscana and the Po valley. Natural infections by elm yellows phytoplasma (now Phytoplasma ulmi) were recorded in U. minor and U. pumila. In Europe, little information was so far available on possible vectors of elm yellows. Recently, in the Friuli Venezia Giulia region of Italy, several elm trees showing symptoms of elm yellows were observed. On the basis of symptomatology (yellowing, witches’ broom, small leaves), it was estimated that approximately a hundred trees were infected in a few limited areas but their infection patterns suggested the presence of active vectors. Investigations were done from 2000 to 2002 in the areas of Cornino, Trieste, Gorizia and Moruzzo. Using PCR assays and RFLP, Phytoplasma ulmi was detected in symptomatic trees (U. minor and U. pumila), as well as in a few asymptomatic trees. Several insect species were also collected from elm trees (Aphrodes sp., Aphrophora alni, Hyalesthes luteipes, Iassus scutellaris, Issus sp. Macropsis mendax, Metcalfa pruinosa, Philaenus spumarius). Among these species, only Macropsis mendax tested positive for elm yellows phytoplasma by PCR. Transmission studies demonstrated that M. mendax is a vector of elm yellows phytoplasma. This monophagous insect has one generation per year on elm, where it overwinters as eggs, but more studies are needed on its efficiency as a phytoplasma vector. During this study, it was also found that alder trees (Alnus glutinosa) growing in the vicinity of diseased elms were infected by alder yellows (a closely related phytoplasma belonging to Elm Yellows group 16SrV, transmitted by Oncopsis alni). It was experimentally possible to transmit by grafting the alder yellows phytoplasma to U. minor.
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* EPPO Secretariat note: although the relationships between European and American phytoplasmas found on elm trees need to be further investigated (see also EPPO RS 2003/095), it appears necessary to review the quarantine status of ‘Elm phloem necrosis phytoplasma’.
Sources
Carraro L, Ferrini F, Ermacora P, Loi N, Martini M, Osler R (2004) Macropsis mendax as a vector of elm yellows phytoplasma of Ulmus species.
Plant Pathology, 53(1), 90-95.