Surveying Potential Vectors of Apple Proliferation Phytoplasma: Faunistic Analysis and Infection Status of Selected Auchenorrhyncha Species

Abstract

Apple proliferation (AP) is one of the economically most important diseases in European apple cultivation. The disease is caused by the cell-wall-less bacterium ’ Candidatus Phytoplasma mali’, which is transmitted by Cacopsylla picta (Foerster) and Cacopsylla melanoneura (Foerster) (Hemiptera: Psylloidea). In South Tyrol (Italy), severe outbreaks were documented since the 1990s. Infestation rates of AP do not always correlate with the population densities of the confirmed vectors, implying the presence of other, so far unknown, hemipterian vectors. By elucidating the species community of Auchenorrhyncha (Insecta: Hemiptera) at a regional scale, more than 31,000 specimens were captured in South Tyrolean apple orchards. The occurrence of 95 species was confirmed, whereas fourteen species are new records for this territory. Based on the faunistical data, more than 3600 individuals out of 25 species were analyzed using quantitative PCR to assess the presence of AP phytoplasma. The pathogen was sporadically detected in some individuals of different species, for example in Stictocephala bisonia Kopp and Yonk (Hemiptera: Membracidae). However, the concentration of phytoplasma was much lower than in infected C. picta and C. melanoneura captured in the same region, confirming the role of the latter mentioned psyllids as the main insect vectors of AP- phytoplasma in South Tyrol.

Identification of Plant DNA in Adults of the Phytoplasma Vector Cacopsylla picta Helps Understanding Its Feeding Behavior

“…The host plant of C. picta is known and it has been suggested [17], but not proven, that adult psyllids also feed on other plant taxa. C. picta can survive for up to four days without food (Figure A2), but the insect lives for only four or five months a year on its host [19,20]. This leads to the conclusion that C. picta must feed from plants other than Malus.…”

“…In northern Italy, C. picta's reproduction takes place from mid-March until the beginning of August [19,20]. During this period, the overwintered adults-the so-called remigrants-of C. picta can be detected in apple orchards until the beginning of June, while the young adults of the new generation-the so-called emigrants-occur from the end of June until the beginning of August [19,20]. During the rest of the year, adults of C. picta dwell on shelter plants, mostly conifers at higher elevations [21].…”

Molecular Characterization of Mitogenome of Cacopsylla picta and Cacopsylla melanoneura, Two Vector Species of ‘Candidatus Phytoplasma mali’

“…Both species are vectors of 'Ca. Phytoplasma mali' (apple proliferation phytoplasma) [8][9][10], the causal agent of apple proliferation…”