Phytoseiid mites (Acari: Gamasina) in Finnish apple plantations with reference to integrated control of phytophagous mites

Authors

• Tuomo Tuovinen Department of Animal Husbandry, University of Helsinki, SF-00710 Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72680

Abstract

On apple tree leaves, the most abundant predatory phytoseiid species were Euseius finlandicus (Oudemans), comprising 39% of specimens found in surveys in 1985 and 1989, Phyloseius macropilis (Banks), 32%, and Paraseiulus soleiger (Ribaga), 18%. Amblyseius subsotidus (Beglyarov) and A. reductus Wainstein occurred occasionally in relatively high densities, whereas Anlhoseius rhenanus (Oudemans), A. suecicus (Sellnick), A. richteri (Karg), A. bakeri (Carman), A. viktorovi Wainstein, Paraseiulus taihii (Athias-Henriot) and P. triporus (Chant & Yoshida-Shaul) occurred rarely and always in low densities. On unsprayed trees, the mean density of phytoseiid mites was 1.2 mites/leaf. On sprayed trees, none or only a few phytoseiids were found, but the density of the European red spider mite Panonychus ulmi (Koch) was much higher than on unsprayed trees. Indigenous phytoseiid mites appeared to be capable of maintaining the P. ulmi population level under the economic threshold on unsprayed apple trees. The presence of the common prey mites, P. ulmi, the rust mite Aculus schlechtendali (Nalepa), or tydeid mites was not necessary for the presence of phytoseiid mites. Relatively high numbers of E. finlandicus, P. macropilis and P. soleiger were found, although prey mites were scarce. Many deciduous trees and bushes support high populations of phytoseiid mites. The highest numbers were found on Aesculus hippocastani, Corylus avellana, Fraxinus excelsior, Ribes nigrum. Rubus odoralus, Sorhus aucuparia, Tilia spp. and Ulmus glabra. E. finlandicus occurred most commonly and in the highest densities, followed by P. macropilis, P. soleiger, P. triporus and A. rhenanus. E. finlandicus can immigrate rapidly from adjacent vegetation into an orchard after harmful spraying if suitable plants are present, and tall trees appeared to be more important than low bushes as natural sources of phytoseiids for aerial dispersal. In acaricide tests, flubenzimine was effective against P. ulmi, but it was harmful to E. finlandicus and P. macropilis. A single treatment with clofentezine and hexythiazox, although effective against P. ulmi, was harmless to E. finlandicus and P. macropilis, but repeated sprays of both acaricides significantly reduced the density of phytoseiids. The fungicides dithianon and bitertanol were harmless to phytoseiids, but dichlofluanid was harmful. Triforine sprays also reduced the numbers of phytoseiid mites, but the effect was only temporary. It had a 75% effect on P. ulmi winter eggs when sprayed just before hatching. Dichlofluanid was effective against P. ulmi and A. schlechtendali.