Establishment of a permanent rearing of Cacopsylla picta (Hemiptera: Psylloidea), the main vector of ‘Candidatus Phytoplasma mali’ in Germany

The univoltine psyllid Cacopsylla picta (Foerster) is the main vector of ‘Ca. Phytoplasma mali’ in Germany, the causal agent of apple proliferation, an economically important disease of apple in Europe. Its population dynamics on its host plant apple (Malus spp.) and migration to coniferous shelter plants for overwintering have been described for Southwest Germany. Temporary greenhouse rearing under controlled conditions, starting from field-collected overwintered adults, was set up to produce homogeneous offspring. New generation adults were transferred to conifers in the greenhouse at the beginning of the natural migration phase to obtain a continuous rearing spanning the aestivation and hibernation period. However, efforts to directly overwinter C. picta on different conifer species failed. The natural overwintering sites were therefore identified and their climatic conditions, mainly moderate summer temperatures with increased humidity and natural cold winter conditions including frost were reproduced. Teneral individuals of the new generation did not switch instantaneously from host plants to conifers. Successful overwintering under experimental conditions was only achieved using a gradual host plant transfer. By incorporating these key factors two continuous rearings of C. picta were maintained over 3 years with both, spruce and pine, as suitable shelter plants. This is the first report of a permanent rearing of C. picta under experimental conditions. Our data show experimentally that C. picta is univoltine and that conifers act only as shelter plants for overwintering and not as hosts for reproduction.