Worldwide a great variety of eriophyoid mites inhabit forest canopy trees and ornamental plants that are used in city parks, squares and boulevards. An analysis of the relevant bibliography portrays only a fragmentary knowledge and the majority of our information concerns the temperate zone. Three case studies are presented as examples of different approaches to solve problems connected with eriophyoid mites of forest and ornamental trees. The first example deals with eriophyoids of a temperate zone forest in a natural environment, focusing on conifers which represent the largest component. The second case study documents a possible approach to obtain greater knowledge and control of the bud mite species, Trisetacus juniperinus (Nalepa) on Cupressaceae. This is a harmless species in the natural environment which becomes a serious pest in nurseries and young stands of Cupressus sempervirens in the Mediterranean region. The final case study reports on long-term studies carried out in Poland on injurious eriophyoid species that are found in nurseries, city greenery and parks. This paper also discusses future perspectives for research on eriophyoid mites living on forest and ornamental plants.

The cabbage whitefly (CW), Aleyrodes proletella (L.) (Hemiptera: Aleyrodidae), is an important pest in Brassica oleracea L. crops. Little is known about the mechanisms of resistance to CW of savoy cabbage and kale cultivars. Light microscopy (LM) and scanning electron microscopy (SEM) analysis were used to determine the relationship between the morphological and anatomical features of savoy cabbage (Brassica oleracea L. convar. capitata (L.) Alef. var. sabauda L.) and kale (Brassica oleracea L. convar. acephala (DC.) Alef. var. sabellica L.) leaves and host suitability to colonization by CW. Two kale cultivars, “Redbor” and “Starbor”, and two savoy cabbage cultivars, “Gloriosa” and “Alcosa”, that differed in the degree of infestation by A. proletella were taken for histological analysis. The lowest infestation by all forms of A. proletella was observed on savoy cabbage cultivar “Alcosa” and kale cultivar “Starbor”. The reduced colonization by cabbage whitefly may be related to the structure of the epidermis and the anatomical features of the leaf. The leaves of “Starbor” and “Alcosa” had more folds in the epidermis, less numerous but larger stomata, and a more compact mesophyll structure compared to “Redbor” and “Gloriosa”. In both analysed species, there was no clear relationship between the thickness of the abaxial epidermal layer, thickness of the lamina, number of vascular bundles, and degree of infestation by the cabbage whitefly. This study identified promising sources of resistance to A. proletella among cultivars of savoy cabbage and kale. Varying infestation by CW was associated with morphological and anatomical characteristics of leaves. Further study is needed to confirm the relationship between insect resistance and leaf surface and morphological characteristics of leaves in a broader range of Brassica spp.

The species composition of jumping plant-lice, especially Cacopsylla pruni as a vector of 'Candidatus Phytoplasma prunorum', was researched on stone fruit trees in 53 locations, mainly in Central Poland. Twelve species were found to belong to the families Psyllidae, Aphalaridae and Triozidae. C. pruni which made up 59.9% of the collected specimens was noted in eight locations in plum orchards and in two locations in cherry orchards. Only three locations were found to have specimens of C. pruni which were infected by 'Ca. Ph. prunorum', namely on plum trees in the Lesser Poland Province and plum and mirabelle plum trees in the Masoovian Province. In the latter location, specimens of C. pruni infected with 'Ca. Phytoplasma asteris' were also caught in mirabelle plum trees. We can conclude that at this moment C. pruni is not a significant threat to Polish stone fruit orchards and its importance in the possible spread of phytoplasma causing European stone fruit yellows is low.

Plum pox virus (PPV) is the causal agent of sharka, the most devastating virus disease of Prunus species. PPV is transmitted by vegetative propagation, particularly by grafting, as well as by aphid species in a nonpersistent manner. The objective of this paper was to evaluate the prevalence and diversity of PPV‐vector aphid species in representative European areas of prunus cultivation. Four experimental nursery plots were established in Skierniewice (Poland), Liria (Spain), Plovdiv (Bulgaria) and Bistrita (Romania). Aphid population was weekly monitored using the sticky shoot method in spring and/or autumn in each nursery plot. Furthermore, we estimated the relative efficiency factor for the main PPV‐vector aphid species using bibliographic and reference data. Aphid diversity in each nursery plot was assessed using the Shannon index and the number of estimated aphid species was calculated by the rarefaction method. The highest diversity of aphid species population was reported in Plovdiv in spring while the lowest diversity was found in Liria in spring. A cluster analysis based on Morisita–Horn similarity index was performed to study the differences in species composition between the four nursery plots and seasons. Aphid population was clearly grouped by location and season. Results showed Aphis spiraecola and Hyalopterus pruni complex were typically spring aphid species, while Anoecia corni and Rhopalosiphum padi dominated autumn catch. Regarding PPV‐vector aphid species present in nursery plots, A. spiraecola was the most prevalent PPV‐vector aphid species in Liria and in Bistrita, showing a high relative efficiency factor of PPV transmission (0.91). Consequently, A. spiraecola should be considered a key actor in the spread of PPV in these regions. Hyalopterus pruni complex was the most prevalent PPV‐vector aphid species in Skierniewice and Plovdiv, showing a very low relative efficiency factor of PPV transmission (0.09). Therefore, the role of H. pruni complex in spread of PPV in these regions can be considered negligible. Furthermore, we statistically demonstrated that the presence of specific PPV‐vector aphid species is associated with the spread of the disease, whereas the biodiversity of aphid species population does not affect the spread of PPV. Finally, the advantages of the use of vector pressure index in the management of sharka disease are discussed.

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