An overview of chelicerate ovaries, with special reference to mites - myths and facts.

In arthropods of the subphylum Chelicerata a panoistic ovary, in which all germline cells differentiate into oocytes, prevails. Among the chelicerates, mites are believed to show a great variety of the structure of the female gonads. In general, the knowledge of the ovarian structure in mites is fragmentary and patchy. In both evolutionary lines, Acariformes and Parasitiformes, apart from the panoistic ovary, the meroistic ovary, in which the oocytes grow supported by their sibling cells, the nurse cells, occurs. The presence of the meroistic ovary is considered an apomorphic state. Previous studies revealed a various structure of the meroistic ovary in different mite taxa, and the differences came down, inter alia, to a different number and location of the nurse cells in relation to the oocytes. Here we provide a comprehensive review of the structure of the Chelicerata ovary, with special reference to the mite ovary. We also provide our preliminary results of the analysis of ovarian structure in two representatives of terrestrial Parasitengona (Acariformes), Allothrombium fuliginosum (Trombidiidae) and Erythraeus cinereus (Erythraeidae), performed using light, confocal and electron transmission microscopy. The analyses allowed for verification of data published before. In A. fuliginosum we showed the presence of the nurse cells in the ovarian wall, so the ovary should be classified as meroistic. In meroistic ovary of E. cinereus we found that each oocyte is connected to several mononucleated nurse cells. The verification of literature data and broadening the knowledge of the structure of the female gonad in mites, will result in estimating the usefulness of the ovary traits in phylogenetic analyses and will provide the basis for inference about the directions of evolutionary changes of female gonad at lower systematic levels.

Chigger mite (Acariformes: Trombiculidae) infestation in reed passerine birds in Central Europe: a case of the bearded tit Panurus biarmicus.

Larval trombiculid (chigger) mites are common ectoparasites of terrestrial vertebrates including humans, causing itching and skin inflammation known as trombiculiasis. Investigation of their diversity, distribution and seasonal abundance is therefore important from a veterinary and public health point of view. Although researchers have paid increased attention to these parasites in recent years, there is still little ecological data available on chiggers associated with birds inhabiting different types of habitats such as wetlands, for example. In 2021, we investigated the mite fauna in a specialist reedbed passerine, the bearded tit (Panurus biarmicus), and their effects on this host in the south-west Slovakia, Central Europe. A total of 1134 larvae of 1 mite species Blankaartia acuscutellaris were found in 99 out of 267 examined bearded tits. Juveniles were more infested than adult birds, but no differences were found between sexes. The larvae of mites first appeared on the host during the second half of June and peaked in the second half of July. After that, their numbers decreased gradually until October. Despite the relatively high prevalence and intensity of mite infestation in the bearded tit, no differences in body condition between infested and uninfested birds suggest that infestation by B. acuscutellaris may not have serious negative effects on the host health. Bearded tits can therefore be a reliable indicator of the presence of the chigger mites in wetland habitats.

One-way ticket to the blue: A large-scale, dated phylogeny revealed asymmetric land-to-water transitions in acariform mites (Acari: Acariformes).

Acariform mites are an ancient and megadiverse lineage that may have experienced a complex pattern of invasions into terrestrial and aquatic habitats. These among-realm transitions may relate to periods of turmoil in Earth's history or be simply results of uneven biodiversity patterns across habitats. Here, we inferred a dated, representative acariform phylogeny (five genes, 9,200 bp aligned, 367 terminals belonging to 150 ingroup plus 15 outgroup families, 23 fossil calibration points) which was used to infer transitions between marine/freshwater/terrestrial habitats. We detected four unambiguous transitions from terrestrial to freshwater habitats (Hydrozetes, Naiadacarus, Fusohericia, Afronothrus, Homocaligus); one from freshwater to marine (Pontarachnidae), and four from marine to brackish or freshwater transitions (all among Halacaridae: Acarothrix; Halacarellus petiti; Copidognathus sp.; clade Limnohalacarus + Soldanellonyx + Porohalacarus + Porolohmannella). One transition to the sea was inferred ambiguously with respect to the ancestor being either terrestrial or freshwater (Hyadesiidae), and another must be most carefully examined by adding potential related taxa (Selenoribatidae + Fortuyniidae). Finally, we inferred a single, remarkable transition from aquatic to terrestrial habitats involving early evolution of the large and ecologically diverse lineage: the ancestor of the Halacaridae + Parasitengona clade was probably freshwater given our dataset, thus making terrestrial Parasitengona secondarily terrestrial. Overall, our results suggested a strong asymmetry in environmental transitions: the majority occurred from terrestrial to aquatic habitats. This asymmetry is probably linked to mites' biological properties and uneven biodiversity patterns across habitats rather than Earth's geological history. Since the land holds more acariform diversity than water habitats, a shift from the former is more likely than from the latter. We inferred the following relationships: alicid endeostigmatid + eriophyoid (Alycidae, (Nanorchestidae, (Nematalycidae, Eriophyoidea))) being sister group to the remaining Acariformes: (proteonematalycid Endeostigmata, alicorhagiid Endeostigmata, Trombidiformes, Oribatida (including Astigmata)). Trombidiform relationships had several novel rearrangements: (i) traditional Eupodina lacked support for the inclusion of Bdelloidea; (ii) Teneriffidae, traditionally placed among Anystina, was consistently recovered in a clade including Heterostigmata in Eleutherengona; (iii) several lineages, such as Adamystidae, Paratydeidae, Caeculidae and Erythracaridae, were recovered in a large clade along other Anystina and Eleutherengona, suggesting single origins of several fundamental character states, such as the reduction of the cheliceral fixed digit and development of the palpal thumb-claw complex.

Charletonia rocciai treat and Flechtmann, 1979 (Trombidiformes: Erythraeidae): larval redescription and new records for Brazil

The family Erythraeidae has 60 genera worldwide, of which Charletonia Oudemans has 86 described species, only two of which are recorded in Brazil. Here, we redescribe one of these species based on the holotype, Charletonia rocciai Treat and Flechtmann, and newly collected material. The material represents new records from four different localities in São Paulo State and one in Santa Catarina State. In addition, we provide SEM images of the morphological structures to improve the diagnosis and redescription, an updated distribution map, including biological data, and new host-associations of C. rocciai with the following orders of insects, Coleoptera and Thysanoptera, and with an order of Arachnida – Araneae.

Stylostome formation by parasitic larvae of Allothrombium fuliginosum (Trombidiformes: Trombidiidae): morphology of feeding tubes and factors affecting their size.

The morphology and formation of stylostomes (feeding tubes) in hosts' body during the parasitic phase of Allothrombium fuliginosum (Hermann) larvae were studied for the first time with light microscopy (LM) and transmission electron microscopy (TEM). The stylostomes were observed in three aphids species-Acyrthosiphon pisum (Harris), Elatobium abietinum (Walker), and Macrosiphum rosae (L.)-parasitized by mites under laboratory conditions. They consisted of 2-6 main branches, preliminarily unbranched, then producing secondary and sometimes also tertiary branches as finally formed structures. Their walls were uniformly electron-dense, without any longitudinal and transverse stratifications and showed rather irregular outlines. Distally, the stylostome branches revealed transparent pores and cavities in their walls, connecting the stylostome canal with surrounding haemocoelic space. The total length of stylostomes at the end of the parasitic phase was on average 16× greater than that recorded in the youngest stylostomes. No differences in the overall shape of feeding tubes between host species were stated. The stylostomes formed in different host species did not differ significantly, except their total length, which attained the highest value in tissues of Ac. pisum.

Erythraeus (Parerythraeus) thomasi sp. nov. (Acari: Actinotrichida: Erythraeidae) from Finland, with a redefinition of Parerythraeus Southcott, 1946 stat. nov. as a subgenus and a key to species.

Erythraeus (Parerythraeus) thomasi sp. nov. is described and illustrated based on specimens collected from Finland. Parerythraeus Southcott, 1946 stat. nov., previously synonymized with Erythraeus Latreille, 1806, is considered a subgenus of Erythraeus. Thirteen species, including E. (P.) thomasi, are included in this subgenus, and a differential diagnosis is provided for the 12 adequately described species. A key to all known species of Erythraeus (Parerythraeus) is also provided.

A new species of Leptus (Leptus) (Trombidiformes: Erythraeidae) and new records of Leptus (Leptus) haitlingeri Jacinavicius, Bassini-Silva & Welbourn, 2019 for Brazil

Erythraeidae Robineau-Desvoidy has 60 genera worldwide, of which Leptus Latreille has around 260 species described, with 15 of these recorded from Brazil. Here, we describe Leptus (Leptus) flechtmanni sp. n. from a cave in the state of Pará. Additional material attributed to this species is reported from other caves and also parasitizing a harvestman. In addition, SEM images and new Brazilian host records (Diplopoda and Hemiptera) are presented for Leptus (Leptus) haitlingeri from the states of São Paulo and Rio de Janeiro.

A novel symbiotic relationship between mites and recluse spiders (Sicariidae: Loxosceles), with a description of a new Callidosoma species (Trombidiformes: Erythraeidae).

This study reports a symbiotic association between an unknown species of Loxosceles (Araneae: Sicariidae) and the adults of a new species of parasitengone mite that lives on their web in Brazilian caves. This mite is described as Callidosoma cassiculophylla sp. nov. (Parasitengona: Erythraeidae). The symbiotic association is clearly beneficial for the mite, which lives with the spider, and feeds on prey captured by their webs, without any aggressive behavior or expulsion of the mites by the spiders.

Comparative ultrastructure of coxal glands in unfed larvae of Leptotrombidium orientale (Schluger, 1948) (Trombiculidae) and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae).

Coxal glands of unfed larvae Leptotrombidium orientale (Schluger, 1948) (Trombiculidae), a terrestrial mite parasitizing vertebrates, and Hydryphantes ruber (de Geer, 1778) (Hydryphantidae), a water mite parasitizing insects were studied using transmission electron microscopy. In both species, the coxal glands are represented by a paired tubular organ extending on the sides of the brain from the mouthparts to the frontal midgut wall and are formed of the cells arranged around the central lumen. As in other Parasitengona, the coxal glands are devoid of a proximal sacculus. The excretory duct, joining with ducts of the prosomal salivary glands constitutes the common podocephalic duct, opening into the subcheliceral space. The coxal glands of L. orientale are composed of a distal tubule with a basal labyrinth, an intermediate segment without labyrinth, and a proximal tubule bearing tight microvilli on the apical cell surface and coiled around the intermediate segment. The coxal glands of H. ruber mainly consist of the uniformly organized proximal tubule with apical microvilli of the cells lacking the basal labyrinth. This tubule shows several loops running backward and forward in a vertical plane on the side of the brain. In contrast to L. orientale, larvae of H. ruber reveal a terminal cuticular sac/bladder for accumulation of secreted fluids. Organization of the coxal glands depends on the ecological conditions of mites. Larvae of terrestrial L. orientale possess distal tubule functioning in re-absorption of ions and water. Conversely, water mite larvae H. ruber need to evacuate of the water excess, so the filtrating proximal tubule is prominent.

Comparative stylostome ultrastructure of Hirsutiella zachvatkini (Trombiculidae) and Trombidium holosericeum (Trombidiidae) larvae.

Stylostomes (feeding tubes) of Hirsutiella zachvatkini (Schluger) (Trombiculidae), feeding on bank voles [Myodes glareolus (Schreber)], and of Trombidium holosericeum (L.) (Trombidiidae), feeding on larvae of Stenodemini sp. (Heteroptera, Miridae), were studied by TEM methods and on semi-thin sections. The stylostome of H. zachvatkini is a homogeneous structure of low electron density and without strict margins. It extends within the concave host epidermis, undergoing hyperplasia and hyperkeratosis. TEM does not reveal any obvious stratification in the stylostome walls. The cheliceral movable digits are moved apart by 5-6 µm and tightly applied/adhered to the stylostome substance. A local area beneath the open end of the stylostome canal is not empty but contains a nearly homogeneous substrate, which can pass into the central stylostome canal. The latter is mostly free of contents. In contrast to H. zachvatkini, larvae of T. holosericeum form a root-like stylostome chaotically branching within the clear space underneath the host cuticle free of tissue elements. Tubules of the distal stylostome branches become progressively thinner and disappear blindly. As in H. zachvatkini, the stylostome walls of T. holosericeum are devoid of stratification but show moderate to high electron density. The cheliceral movable digits are moved apart by the same distance, as in H. zachvatkini, and tightly applied to the stylostome substance. The lumen of the central canal is either electron lucent, in the distal portions, or filled with a fine granular or homogeneous substrate of low electron density in the proximal portions forming a type of ampoule. This study shows that Trombiculidae and Trombidiidae share similar initial stages of stylostome formation but the resultant stylostome of each family is distinctly different.

The first description of a microtrombidiid mite (Actinotrichida: Prostigmata, Microtrombidiidae) from Baltic amber, with notes on related extant genera and species.

Discovery of parasitengone mites (Acari) in the Gulf of Gdansk deposits of Baltic amber ("Blue Earth" sediment) resulted in the first description of a fossil representative of Microtrombidiidae. The new species, based on larvae, displays affinity to recent members of Montenegtrombium Saboori and Pesic, 2006, Persianthrombium Sedghi, Saboori and Hakimitabar (in Sedghi et al. 2010) and Porttrombidium Haitlinger, 2000, known from the southwestern Palaearctic. A comparison with related genera and species places the newly described taxon in Porttrombidium (as Porttrombidium gedanense sp. nov.). Montenegtrombium is regarded as a junior synonym of Porttrombidium.

Planthopper (Hemiptera: Flatidae) parasitized by larval erythraeid mite (Trombidiformes: Erythraeidae)-a description of two new species from western Madagascar.

Descriptions of Dambullaeus adonis Makol et Moniuszko SP NOV: (Trombidiformes: Erythraeidae, Callidosomatinae) and Latois nigrolineata Swierczewski et Stroinski SP NOV: (Hemiptera: Fulgoromorpha, Flatidae) from Madagascar are provided. The first host record for ectoparasitic larvae of Dambullaeus Haitlinger, 2001 and the first evidence on host-parasite association between flatid adult and erythraeid larvae are given. Genus Dambullaeus, known exclusively from larvae and now comprising two species of Gondwanan distribution, is critically reappraised.