Effect of Daytime and Tree Canopy Height on Sampling of Cacopsylla melanoneura, a ‘Candidatus Phytoplasma mali’ Vector

Abstract

The psyllids Cacopsylla melanoneura and Cacopsylla picta reproduce on apple (Malus × domestica) and transmit the bacterium ‘Candidatus Phytoplasma mali’, the causative agent of apple proliferation. Adult psyllids were collected by the beating-tray method from lower and upper parts of the apple tree canopy in the morning and in the afternoon. There was a trend of catching more emigrant adults of C.melanoneura in the morning and in the lower part of the canopy. For C.melanoneura remigrants, no differences were observed. The findings regarding the distribution of adults were reflected by the number of nymphs collected by wash-down sampling. The density of C.picta was too low for a statistical analysis. The vector monitoring and how it is commonly performed, is suitable for estimating densities of C.melanoneura. Nevertheless, above a certain temperature threshold, prediction of C.melanoneura density might be skewed. No evidence was found that other relatively abundant psyllid species in the orchard, viz. Baeopelma colorata, Cacopsylla breviantennata, Cacopsylla brunneipennis, Cacopsylla pruni and Trioza urticae, were involved in ‘Candidatus Phytoplasma mali’ transmission. The results of our study contribute to an advanced understanding of insect vector behavior and thus have a practical impact for an improved field monitoring.

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

“…Considering that we found a broad range of plant DNA from different genera in C. picta, it can be assumed that these psyllids also feed on or probe other plants in the surrounding of the host plant, even during their presence in the apple orchard. Psyllids are short-term flyers or they move by jumping; additionally, their movement is undirected and their activity is temperature-dependent [69][70][71][72]. Thus, it is unlikely that psyllids can actively overcome large distances, but they can be passively transported over longer distances by wind [21][22][23].…”

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

“…It is thus likely that other factors than unknown vectoring insects are attributable to the—in some years—observed discrepancy between low population densities of C. picta and C. melanoneura but elevated incidences of AP symptomatic apple trees in the following year. Available monitoring tools for psyllids are error-prone and could underestimate the actual insect populations [ 30 , 86 , 87 , 88 ]. Transmission of AP phytoplasma can also occur via root bridges [ 89 , 90 ] or through grafting of infected propagation material [ 91 ], and might skew the correlation between insect vector presence and the occurrence of symptomatic trees.…”