No abstract

Soil mites in lowland pastures grazed by sheep, cattle and horses and hay-growing meadows were investigated near Bydgoszcz. Samples were taken in spring, summer and autumn of 2001 and 2002 from the lower parts of plants (0-3 cm) and 2 soil layers, 0-3 cm and 3-6 cm. The grazing animals reduced the density of mites and species richness of Oribatida as compared to the control plots. The impact of sheep and cattle grazing on mites was higher than that of horses. Among the mites the Oribatida predominated, while the Gamasida were less abundant. Some species preferred the meadows while others preferred the pastures. Liebstadia similis predominated in the pastures grazed by sheep and cattle and Heminothrus peltifer-on those grazed by horses. Most mites inhabited the lower parts of plants; their density in the soil decreased with soil depth.

The study involved three pastures, grazed by geese, goats and fallow deer, and three nearby meadows (control plots) situated in north-central Poland. Samples of 150 cm3 each (6 cm of soil and 3 cm of lower parts of plants) were collected in spring, summer and autumn 2016 and 2017 in 10 replications, 360 samples in total. This material included 22.561 mites, among which Oribatida accounted for 69%, Mesostigmata for 21%, and other mites for 10%. At most study sites, both pastures and meadows, no significant seasonal differences in the abundance of Oribatida and Mesostigmata were seen. Such differences were only observed for the third category of other mites that were the most abundant in spring and usually the least abundant in autumn. Also species diversity of Oribatida differed between the seasons – in all pastures it was the highest in summer and the lowest in spring, while in all meadows it was the highest in spring and decreased towards autumn. Oribatid species were more affected by the habitats than by seasons, as some species were strongly associated with pastures (Platynothrus peltifer), other with meadows (Achipteria coleoptrata, Liebstadia similis, Metabelba pulverosa, Scheloribates laevigatus and Sellnickochthonius immaculatus), and some (Eupelops occultus and Tectocepheus velatus) were abundant in both habitats. Although the effect of seasonality was weaker than that of the habitat, it was still perceptible. Platynothrus peltifer was most associated with autumn, T. velatus with spring, E. occultus with spring and summer and L. similis with summer.

The morphological ontogeny of Adoristes ovatus (C.L. Koch, 1839) is described and illustrated. The adult has the interlamellar seta shorter than the lamella and the translamella is usually absent, but can also be incomplete, or present as a thin line. The juveniles are unpigmented, oval in cross-section, with thin and smooth prodorsal and gastronotal setae, and with the anal opening in the posteroventral position, which is typical of xylophages. The legs and claws of juveniles are relatively thick, especially leg I, and the leg setae are smooth or with short barbs. All juveniles have a sclerotized semicircle located anterior to each prodorsal seta le. The larva has 11 pairs of gastronotal setae, the nymphs have 12 pairs, without the d-series. The mean body length of females is larger than males, but varies greatly among samples (445–735 μm) and the largest females can be 1.5 times longer than the smallest males. The sex ratio and the number of gravid females also vary among samples. We provisionally consider Adoristes (Gordeeviella) Shtanchaeva, Subías & Arillo, 2010 a junior synonym of Adoristes Hull, 1916.