Abstract
Simple SummaryCacopsylla melanoneura is a psyllid vector of the phytoplasma ‘Candidatus Phytoplasma mali’, the causal agent of apple proliferation. It spends part of the year in apple orchards, then moves to conifers for aestivation and overwintering. The aim of this work was to analyze the quantity of phytoplasma inside the insect body throughout the year, during different life stages, in order to assess the relative acquisition efficiency and the vector infective risk. The phytoplasma was detected in all the life stages. The phytoplasma load significantly increased during the period spent on conifers, but in many cases also nymphs and newly emerged adults contained a sufficient quantity of phytoplasma to consider these stages infective. The obtained results allow us to optimize control strategies against the vector and thus against the spread of the disease.The transmission of phytoplasmas is the result of an intricate interplay involving pathogens, insect vectors and host plants. Knowledge of the vector’s competence during its lifespan allows us to define more sustainable well-timed control strategies targeted towards the most worrisome life stages. We investigated the temporal dynamics of ‘Candidatus Phytoplasma mali’ load in Cacopsylla melanoneura in the different developmental stages in Northwest Italy. The phytoplasma load in the vector was evaluated in overwintering adults, nymphs and newly emerged adults after different acquisition access periods. Moreover, we followed the multiplication of the phytoplasma during the aestivation and the overwintering period on conifers. Our results confirmed the ability of remigrants to retain the phytoplasma until the end of winter. We also highlighted the high acquisition efficiency and vector competence, based on phytoplasma load, of nymphs and newly emerged adults. Therefore, particular attention should be paid to the management of overwintered C. melanoneura as soon as they return to the orchards, but also to newly emerged adults, particularly in orchards with a high infection rate and when the migration to conifers is delayed.
Highlights
Phytoplasmas are wall-less phytopathogenic prokaryotes transmitted by phloem-sucking insects in a persistent propagative manner and are associated with several diseases in both cultivated and wild plants [1]
The complete transmission process is commonly divided into three phases: the acquisition period, the latency period
‘Candidatus P. mali’ was detected in all C. melanoneura developmental stages and a higher acquisition efficiency was observed in the 3rd –5th instar nymphs and newly emerged adults
Summary
Phytoplasmas are wall-less phytopathogenic prokaryotes transmitted by phloem-sucking insects in a persistent propagative manner and are associated with several diseases in both cultivated and wild plants [1]. The study of these parameters can be quite easy in the case of monophagous insects with a simple biological cycle, it can be more complicated in the case of oligophagous or polyphagous vectors with more complex biological cycles Such is the case for most of the psyllid vectors of phytoplasmas that spend a great part of the year on conifers as shelter plants for aestivation and overwintering, even kilometers away from apple orchards [16,17]. Phytoplasma multiplication during aestivation and overwintering on conifers is a phenomenon regulated by complex interactions of biotic and abiotic factors, such as temperature, relative humidity and air pressure due to altitude, which cannot accurately be reproduced in the laboratory
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