Antonella Di Palma

A gallery of the key characters to ease identification of Dermanyssus gallinae (Acari: Gamasida: Dermanyssidae) and allow differentiation from Ornithonyssus sylviarum (Acari: Gamasida: Macronyssidae)

BackgroundDermanyssus 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.MethodsSpecimens of D. gallinae were collected at poultry farms in the Puglia and performed for light and scanning electron microscopy observations, identification and micrographs. Moreover specimens of O. sylviarum were collected separately macerated and mounted on slides for light microscopy observations, identification and pictures.ResultsThe 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 j 1, s 1 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.ConclusionThe 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.

Fine Structure of the Female Genital System in Phytoseiid Mites with Remarks on Egg Nutrimentary Development, Sperm-Access System, Sperm Transfer, and Capacitation (Acari, Gamasida, Phytoseiidae)

The fine structure of the female genital system is described in two phytoseiid species: Phytoseiulus persimilis Athias-Henriot (mating females) and Typhlodromus rhenanoides Athias-Henriot (overwintering females). The female genital tract is composed of an unpaired gonad, the uterus (oviduct I), and the vaginal duct (oviduct II). The latter leads to the vagina (genital atrium), into which a pair of vaginal glands opens. The gonad (ovary s.l.) has two components: the ovary (s.str.) where germ cells develop and the lyrate organ serving as a nutrimentary compartment. In the ovary (s.str.), somacells and germ cells are observed. The germ cells surround a central tissue, to which they have direct contact with a nutritive cord at least in the previtellogenic phase during oogenesis. In fertilized females, cells likely representing capacitated sperm cells are also found in the ovary. The lyrate organ has two arms that extend anteriorly but join in their posterior part in front of the ovary (s.str.). The lyrate organ is composed of a somatic (supporting) and a nutritive tissue. The nutritive tissue, which is a syncytium, is continuous with the central tissue. The uterus starts from the ventral region of the central tissue. Finally, the ultrastructure of the sperm-access system, composed of paired solenostomes, major and minor ducts, emboli, calyces, and vesicles, is reported and functional aspects are discussed. The minor ducts end in the somatic tissue of the ovary s.str. However, because of its extremely reduced lumen and the peculiar morphology of its beginning, it seems unlikely that the minor duct lumen serves as a simple route for the sperm towards the ovary.

Fine structure of the phytoseiid-type sperm access system (Acari, Gamasida, Phytoseiidae)

Females of Dermanyssina possess, according to present knowledge, two types of sperm access systems: the laelapid and the phytoseiid type. Contrary to the laelapid type, the phytoseiid type is hardly understood regarding structural and functional aspects.

Fine Structure and Functional Morphology of the Spermatodactyl in Males of Heterozerconidae (Gamasida)

Abstract At present, little is known about the biology of Heterozerconidae (Heterozerconina), a very interesting family of gamasid mites. They are podospermic with males having the genital orifice in presternal position and with a sperm transfer process on the chelicerae. This spermatodactyl arises near the basal region of the fixed digit and seems to have a helicoid “duct.” Since they are podospermic, the females show a sperm access system as well. On the other hand, Discozerconidae (also in Heterozerconina) show a slender spermatodactyl arising from the movable digit. Other families among Gamasida have males whose chelicerae are modified as gonopods involved for a direct sperm transfer. Even though behavioral observations support the idea that gonopods are involved in collecting the spermatophores from the male genital opening and transferring them into the female body, still, little is known on the functional morphology and ultrastructure of these gonopods. Here, a preliminary description of the morphology, fine structure and organization of the gonopods in males of Heterozerconidae is reported and the possible functional implications are discussed. Since the position of Heterozerconina has been one of the least understood questions in gamasid systematics, comparing the ultrastructure and organization of the spermatodactyl in Heterozerconidae males with gonopods in other families among gamasid mites (Phytoseiidae and Veigaiidae) might help in better understanding their position in the group.

Morphological adaptations of mite chelicerae to different trophic activities (Acari)

The authors briefly review the current knowledge on the structural organization and functional significance of the chelicerae and their sensory structures among mites of economical interest in agriculture that have been recently investigated for their gnathosoma. The chelicerae of the polyphagous predatory mite Typhlodromus exhilaratus Ragusa (Gamasida, Phytoseiidae) have a rather unspecialized organization and are of chelate type. They function mainly in grasping the prey and other food, while the other mouthparts are adapted to prey wounding, salivary injection and juice suction. In the Honey Bee parasite, Varroa destructor Anderson & Trueman (Gamasida, Varroidae), the chelicerae have almost completely lost the fixed digit while the movable digit is thinner and elongated. The chelicerae participate directly, along with the other mouthparts, only in the perforation of the Honey Bee integument. In the plant-feeder, Penthaleus major (Duges) (Actinedida, Penthaleidae), the movable digit is composed of a long and stout stylet-like structure, and a peculiar basal sclerite which activates the digit movements. During cheliceral protrusion, the stylets may work jointly or independently from each other in piercing the plant surface and causing deep and large wounds. The protruded stylets may justapose each other; they may delimit an intercheliceral channel and may be involved in salivary injection. The fixed digit is a large somewhat soft structure which covers dorsally the pre-oral and supralabral chamber, and is passively involved in juice sieving and sucking. The movable digit of the fungivorous Tarsonemus nodosus Schaarschmidt (Actinedida, Tarsonemidae) is needle-like and articulated with a transverse lever to the second cheliceral article. The basal cheliceral articles are fused together forming a stylophore. The fixed digits partly envelop the movable digits and they are consolidated with the subcapitulum. The stylar morphology suggests an independent piercing action of the movable digits. The phytophagous Two-Spotted Spider mite, Tetranychus urticae Koch (Actinedida, Tetranychidae), and False Red Spider mite, Cenopalpus pulcher (Canestrini & Fanzago) (Actinedida, Tenuipalpidae), have extensively protractable styliform chelicerae. The movable digits are very elongated and stylet-like, originating proximally from the stylophore (fused first cheliceral articles); the fixed digits are partially fused to each other. During cheliceral protrusion, the stylets are forced to be interlocked to each other to delimit an intercheliceral canal which is directly connected to the salivary duct. At the same time, the fused fixed digits are involved in salivary pump functioning. So, the chelicerae play a double role in piercing the plant surface and discharging saliva into the host tissue. In the tiny phytophagous mites of the superfamily Eriophyoidea (Actinedida), the gnathosoma has a strongly derived organization. Fixed and movable digits are both styliform, laminar shaped, and included in a strict frame of nine stylets of different origin which function together in host piercing, salivary injection and juice suction. The short sliding movements of the cheliceral shafts are activated by the unpaired motivator. The chelicerae seem to be mainly involved in deeping the mouthparts into the wounds and partially in salivary injection. In each of the investigated species, chelicerae are provided with putative chemoreceptive sensilla, in addition to other mechanoreceptors, which seem to be strictly involved in food perception and acceptance. As yet, however, an alternative perceptive function cannot be excluded. Key words: Acari, gnathosoma, mouthparts, feeding mechanisms, sensory structures, digitus mobilis, digitus fixus, morphological adaptations, host piercing, salivary injection, basal sclerite, lever, motivator, stylophore.

First ultrastructural observations on a putative sperm access system in veigaiid females (Veigaiidae, Gamasida)

Females of Dermanyssina display a reproductive system composed of a region involved in egg production and laying and another involved in sperm reception and likely storage. This second region is called the sperm access system, and it is related to a peculiar sperm transfer mode known as podospermy. Males have the chelicerae modified as gonopods which possess a peculiar process on the movable digit, the so-called spermatodactyl, which is used for sperm transfer. In Veigaiidae, males are rarely, exceptionally, or never found, and some species are considered to reproduce parthenogenetically. Known veigaiid males have spermatodactyls, sometimes of extraordinary length. The conspecific females have so-called spiral organs located behind coxae IV. It is likely that these organs, not known from other gamasid mites, represent the veigaiid sperm access system. In the present study, first ultrastructural details on these peculiar organs are given comparing a bisexual species (Veigaia sp.) with two species in which males are extremely rare (V. nemorensis and V. cerva). Each of these structures is composed of a major tube starting from the opening, a vesicle-like region, and several minor tubes. In general it is considered to be derived from an entapophysis. Muscles attach to the minor tube region. A general similarity to the phytoseiid type of sperm access systems may be noted. But preliminary observations on the whole genital system of both female and male veigaiids also reveal a resemblance to the genital system in Parasitina. Whether these findings may challenge the current status of Parasitina and/or Dermanyssina will require further investigations.

Morphological, ultrastructural and functional adaptations of the mouthparts in cheyletid mites (Acari: Actinedida: Cheyletidae)

ABSTRACT The cheyletid family includes more than 370 predatory and parasitic species. According to their feeding habit, some are involved in the integrated pest management of stored food, while other species are parasitic both of men and domestic animals. They all suck up liquid food after piercing tissues with their mouthparts showing peculiar adaptations to this feeding behavior. Like in other taxa of mites, the movable digits have been transformed into stylets that reach the tip of the gnathosoma, enclosed into the malapophyses and lateral lips, and enable the mite to pierce the animal tissues. Since the stylets are short, they serve merely for superficial penetration. Reduced fixed digits cover dorsally the infracapitulum and keep in place the stylets with a peculiar overlapping system. The cheliceral bases are proximally completely fused to each other but also fused with the infracapitulum, thus forming a “stylophore capsule.” Food intake is realized through the preoral groove and the food channel thanks to the pumping action of the pharyngeal chamber. Feeding activity is regulated by several sense organs. A three-dimensional reconstruction is provided with dynamic evidences of the functioning.

Ultrastructure of the male chelicerae of hattena cometis domrow (Acari: Gamasida: Ameroseiidae) functioning as gonopods

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. J. Morphol., 2013.

Ultrastructure investigation of the secondary insemination system of the gamasid mite Hattena cometis domrow (Acari: Anactinotrichida: Ameroseiidae).

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. J. Morphol. 274:918–925, 2013.

Ultrastructure of the Male Genital Tract, Spermatogenesis and Spermatozoa of Hattena cometis Domrow (Acari: Gamasida: Ameroseiidae)

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. J. Morphol. 274:1010–1025, 2013.