Background Dermanyssus gallinae (poultry red mite) is a major threat for the poultry industry and is of significant interest for public health. Identification of D. gallinae can be difficult for scientists not familiar with mite morphology and terminology especially when trying to use identification keys. Moreover, this species may easily be confused with another dermanyssoid mite, Ornithonyssus sylviarum (northern fowl mite), which often shares the same hosts and environment. In this study, a series of light and scanning electron micrographs have been used to illustrate the main key characters for identification of D. gallinae and allow its differentiation from O. sylviarum. Results The micrographs used in this study, based on LM and SEM observations, highlight the following important identifying characters of D. gallinae: the prominent shoulders of the dorsal shield and the jagged edges of the shield reticulations, the position of setae j1, s1 and the epigynal pores, and the presence on tibia IV pl of one seta. Additional micrographs highlighting the shape of the dorsal (abruptly narrowed posteriorly) and epigynal (narrowly rounded posteriorly) shields and the chelicera (elongate, with distinct digits) of O. sylviarum enable its differentiation from D.gallinae. Conclusion The photographic support provided here (both LM and SEM pictures) can be considered a practical tool for scientists who are not well acquainted with the morphology of D.gallinae, and who are involved with classical and molecular systematics, veterinary and human health aspects of poultry red mites.

A new species of mites of the family Veigaiidae (Acari, Gamasida) from the USA (Oregon, Mary's Peak) is described and figured.

Tarsonemus flexus Livshitz, Mitrofanov & Sharonov, 1979 is re-described based on females and newly discovered males and larvae from Hungary; its systematic position is also discussed. As a result, the species is transferred to the genus Dendroptus Kramer, 1876. It is speculated that the genus may contain at least two parallel phylogenetic lines.

Many gamasid mites, mainly of the taxon Dermanyssina, possess a secondarily evolved insemination system that is generally described as occurring in two types, the laelapid and the phytoseiid-type, which are structurally considerably different. Considering that Dermanyssina represent the most recent and most diverse group of gamasid mites, it was expected that a greater diversity of insemination system than reflected by the two types could be present and could give an idea of its evolution within the taxon. Here, the authors present a description of the fine-structure of the female secondary insemination system in the dermanyssine mite Hattena cometis. The system consists of a pair of sperm induction pores (solenostomes) and short sperm access ducts (tubules) which end in a syncytium. The syncytial strands of both sides meet medially under the ovary s.str., where they form a spherical syncytial spermatheca. Mature sperm cells of a modified ribbon type were seen in the syncytial parts of the system. The insemination system of Hattena cometis is regarded as a modification of the laelapid type. However, it is much simpler than that of Varroa destructor, the only other gamasid mite with the laelapid type studied ultrastructurally until now, and shows also some structural differences (e.g., no presence of an unpaired sperm duct). Hence, the present study suggests that some intermediate types might be revealed in future ultrastructure studies representing steps in the evolution of the insemination system in the Dermanyssina.

Heterozerconidae is a poorly known, early derived mite family belonging to Heterozerconina (Monogynaspida, Gamasida (= Mesostigmata)). The systematic position of the family is still controversial and little is known about the biology and anatomy of the taxon. In this paper, the gross anatomy, ultrastructure and functional morphology of the female reproductive system are described comparing genera from different geographic areas. The occurence of podospermy (i.e. the use of a sperm transfer process carried by the fixed digit of the male chelicerae to inseminate females through secondary insemination pores instead of through the oviporus) as insemination mode in this family was documented. Nevertheless, morphological and functional evidence in the reproductive system of the females supports the idea that, in the same family, more than one insemination mode is present: some genera are plesiomorphically tocospemic (i.e. insemination through the oviporus) while others switched to podospermy. Such discovery is of fundamental importance for the determination of the relationship between the family Heterozerconidae and the family Discozerconidae, both belonging tentatively to Heterozerconina and for the phylogenetic position of the Heterozerconina among Gamasida.

The ultrastructure and functional adaptations of male chelicerae in Hattena cometis Domrow are discussed. In particular, as in many other gamasid mites, males of Hattena use the chelicerae, modified as gonopods, to transfer the sperm into the female. For such purpose, a slender process extending from the movable digit, the spermatodactyl, is mainly involved. The spermatodactyl is provided with a sperm transfer duct; in H.cometis, the dorsal surface bent and fused with the ventral surface forms this duct so that the spermatodactyl appears as a cuticular process, connected somehow with the movable digit, and folded on itself to delimit the sperm transfer tube. The organization and ultrastructure of the spermatodactyl are discussed and compared with other gamasid mites studied so far.

The ameroseiid mite Hattena cometis has a male genital system that consists of an unpaired, u-shaped testis and paired deferent ducts leading into an unpaired accessory genital gland and ejaculatory duct. The genital opening is located anteriorly immediately in front of the sternal shield. Spermatogenesis is simple, probably due to the haploid nature of the male. Eight stages of spermatogenesis could be roughly distinguished. Mature spermatozoa as found in the deferent duct lumen are peculiar in having a bisected nucleus and numerous peripheral flat chambers, which were formed from indentations of the plasmalemma. In inseminated females, spermatozoa were observed in the syncytial tissue of the sperm access system and in the somatic cells of the ovary. These spermatozoa have achieved a new structure, i.e., an electron-dense plate dividing the cell into two unequal halves. The dense plate has an intricate substructure. Its function is unknown. These sperm cells are considered to represent capacitated spermatozoa. The peripheral chambers are reduced in number inside the female. Similar sperm cells, containing a dense plate, were seen in vacuoles within the epithelium of the deferent duct of one male. These cells are evidently under destruction, but before being completely dissolved had undergone a development leading beyond that of the mature sperm cells found in the deferent duct. Apparently, entering the cell of the deferent duct epithelium or the syncytium tissue triggers the production of the dense plate (or the capacitation process). Our observations are compared with results obtained from other anactinotrichid Acari, mainly Gamasida, and confirm and complete the interpretation of the correlated evolution of components of gamasid reproductive systems.