Histiostoma ovalis (Histiostomatidae, Acari) associated with Ips sexdentatus (Scolytinae, Curculionidae, Coleoptera): ecology and mite redescription on the basis of formerly unknown adults and nymphs

摘要

Histiostomatidae represent a clade within the Astigmata and disperse phoretically by the highly modified deutonymph. A monophyletic species group within the Histiostomatidae, the bark-beetle-clade, includes mites associated with bark beetles (Scolytinae). Histiostoma ovalis Muller, 1860, only known by the morphology of its deutonymph, is a member of this clade. Since almost 150years other developmental stages of the mite were never described. Thus we hereby present adults and nymphal instars of H. ovalis for the first time and designate a neotype. Mites were reared starting from phoretic deutonymphs, collected from adults of Ips sexdentatus and from its original galleries, found in Southern Italy and Germany. Additional deutonymphs were examined from the Slovak Republic and Croatia. During the last 60years there has been confusion about the identity of two species, Histiostoma ovalis Muller, 1860 and H. gladiger Vitzthum, 1926, which were assumed by some authors to be synonymous. We do not contribute new findings about H. gladiger, but in this paper we define the mite, which is usually associated with Ips sexdentatus, as H. ovalis. Almost 100% of adult beetle individuals collected from their galleries in the bark of pine trees were covered with deutonymphs. The average number of deutonymphs per beetle and information of the preferred areas for mite-attachment on the beetle body are presented. Fungal spores were discovered sticking to the cuticle of deutonymphs and other mite instars. Hyperphoresy with deutonymphs of H. ovalis, riding on gamasid mites, which represent also phoretic passengers of I. sexdentatus, was additionally observed.For a better description of H. ovalis, mite specimens from Germany were used to achieve DNA barcoding-sequences. A Baltic amber fossil of an extinct bark beetle, which has four phoretic histiostomatid mite deutonymphs attached to its body, is presented. There is morphological evidence that those deutonymphs could be phylogenetically closely related to H. ovalis.