Water Mite Parasitism Research Articles

The First Report of a Water Mite Unionicola (Trombidiformes: Unionicolidae) Infection in Filopaludina spp. (Gastropoda: Viviparidae) from Thailand with a Description of a New Species of Unionicola (Polyatax) kasetbangkhenensis sp. nov.

Two species of gastropods, Filopaludina sumatrensis polygramma and F. martensi martensi, were found infested with water mites of the genus Unionicola in Bangkok and Nonthaburi provinces, Thailand. Morphological studies on these water mites, based on the characteristics of their genital acetabular and female genital fields, identified them as a new member of subgenus Polyatax. Unionicola (Polyatax) kasetbangkhenensis sp. nov. was named after the first location where this parasitic water mite was discovered. This species is distinguished from others by the pattern of their female genital field, with their anterior acetabular plates each bearing two acetabula and a short thick spine on the inner margin. Additionally, it differs from other species by the structure of the spines in its pedipalps and legs, as well as in the shapes of its coxal plates.

Parasite-host relationships of water mites (Acari: Hydrachnidia) and black flies (Diptera: Simuliidae) in southeastern Spain

BackgroundDocumentation on water mites in Spain is scarce, as is information on the parasite-host relationship between certain water mite species and representatives of the dipteran family Simuliidae. The discomfort caused to humans and animals by black flies seems to be increasing in recent years. In this context, an investigation of parasitic water mites is of great importance, not only from the point of view of biodiversity, but also in terms of their potential to control black fly populations.MethodsRivers across a wide region of eastern Spain were sampled to determine the specific richness of simuliid dipterans and to investigate their possible parasites, such as water mites, mermithid nematodes and microsporidia (fungal microbes). Data on environmental variables, abundance, prevalence and intensity of parasitism on the collected specimens were analyzed.ResultsIn 10 streams, 15,396 simuliid pupae were collected and checked for the presence of water mite larvae; 426 pupae in seven streams were found to be associated with water mite larvae. Of the 21 simuliid species identified based on morphological characters, eight were found to be associated with water mite larvae. Water mite infection was not equally distributed among black fly species. Also, the prevalence of parasitism was low and differed among simuliid species, ranging from one to 13 water mites per black fly pupa. Variation at the intra- and interspecific levels was detected in terms of the number of water mites inside the black fly cocoons. Free-living deutonymphal and adult water mites representing 15 different species of six genera and five families were morphologically identified. The taxonomic identity of the parasitic mite larvae is unclear at present. Morphologically, they fit descriptions of larval Sperchon (Hispidosperchon) algeriensis Lundblad, 1942, but the possibility cannot be excluded that they represent Sperchon algeriensis, the most abundant species at the adult stage in this study and unknown at the larval stage, or even another species of the genus. A molecular analysis produced for the first time cytochrome oxidase I gene sequences for S. algeriensis.ConclusionsOur results contribute to current knowledge on Spanish Hydrachnidia and their relationships with simuliids as hosts. However, further research is needed to evaluate the diversity, distribution, bioecology and prevalence of this parasitism.Graphical

New Molecular-Based Phylogeny of Mussel-Associated Mites Reveals a New Subgenus and Three New Species Representing an Example of a Host-Driven Radiation in Indochina and Confirms the Concept of Division of the Genus Unionicola Haldeman, 1842 (Acari: Unionicolidae) into Numerous Subgenera

Here we describe a new subgenus and three new species of parasitic water mites in the genus Unionicola (Acari: Hydrachnidia) from Myanmar: Myanmaratax subgen. nov., Unionicola (Myanmaratax) savadiensis subgen. and sp. nov. (hosts: Lamellidens savadiensis and L. generosus), U. (My.) generosa sp. nov. (the same hosts), and U. (My.) trapezidenssp. nov. (hosts: Trapezidens dolichorhynchus and T. angustior). These taxa were identified based on a two-gene phylogenetic analysis (COI + 28S), which also confirms the division of the genus Unionicola into numerous subgenera. The new species are cryptic species, which are morphologically indistinguishable but strongly resemble U. (Prasadatax) brandti Vidrine, 1985 described from Thailand (hosts: Lens spp. and Ensidens spp.). We also transfer the latter taxon from Prasadatax to Myanmaratax based on a set of morphological evidence and propose U. (My.) brandti comb. nov. The new subgenus contains a total of five species, one of which needs future sampling efforts and will be described elsewhere. Additionally, 56 valid subgenera, which were placed in the synonymy of the genus and in one case raised to the genus level, are restored here until robust phylogenetic evidence on their taxonomic status is available. Our results also confirm that Unionicola mites are narrow host specialists that are associated with either one or a few closely related freshwater mussel species belonging to one or two sister genera.

Meta-transcriptomics reveals potential virus transfer between Aedes communis mosquitoes and their parasitic water mites.

Arthropods harbor a largely undocumented diversity of RNA viruses. Some arthropods, like mosquitoes, can transmit viruses to vertebrates but are themselves parasitized by other arthropod species, such as mites. Very little is known about the viruses of these ectoparasites and how they move through the host-parasite relationship. To address this, we determined the virome of both mosquitoes and the mites that feed on them. The mosquito Aedes communis is an abundant and widely distributed species in Sweden, in northern Europe. These dipterans are commonly parasitized by water mite larvae (Trombidiformes: Mideopsidae) that are hypothesized to impose negative selection pressures on the mosquito by reducing fitness. In turn, viruses are dual-host agents in the mosquito-mite interaction. We determined the RNA virus diversity of mite-free and mite-detached mosquitoes, as well as their parasitic mites, using meta-transcriptomic sequencing. Our results revealed an extensive RNA virus diversity in both mites and mosquitoes, including thirty-seven putative novel RNA viruses that cover a wide taxonomic range. Notably, a high proportion of viruses (20/37) were shared between mites and mosquitoes, while a limited number of viruses were present in a single host. Comparisons of virus composition and abundance suggest potential virus transfer between mosquitoes and mites during their symbiotic interaction. These findings shed light on virome diversity and ecology in the context of arthropod host-parasite-virus relationships.

Parasitism of Enallagma civile Hagen in Selys, 1853 (Zygoptera: Coenagrionidae) by Arrenurus water mites

We compared the prevalence and intensity of Arrenurus sensu stricto water mite parasites on Enallagma civile Hagen in Selys, 1853 (Zygoptera: Coenagrionidae) from 10 freshwater wetlands (playas) in two different land-cover contexts in western Texas from 2006-2007. Vulnerability to parasitism may be a consequence of disturbance, so we predicted that the more natural form of regional land cover (grasslands) surrounding playas should be associated with a lower water mite load than more disturbed land cover (tilled croplands). Additionally, we examined Arrenurus occurrence and intensity of infection by host sex. Overall prevalence was 38.46% of 130 damselflies sampled having mites; this varied by land-cover type but with opposite trends between years. Overall average parasite load was ~11 water mites per infected host (range: 1-40 mites); intensity was significantly higher in hosts from cropland playas in 2006, but there was no difference by surrounding land cover in 2007. Although there were consistent trends in both years of more males being parasitized than females, the highly uneven distribution of parasites on hosts and differences in average mite load between years generated variability that obscured any statistically significant patterns. Thus, land-cover context surrounding playas, but not host sex, had an impact on parasite load in one of the two years of our study. Future work is needed to identify the mechanisms by which land cover may affect water mite-odonate host-parasite relationships as well as the role of the odonate assemblage as a whole in dispersal of parasites in a temporally dynamic wetland network.

Systematics, distribution and morphology of the newt parasitic water mites of the subgenus Lurchibates Goldschmidt amp; Fu, 2011 (Acari, Hydrachnidia, Hygrobatidae, Hygrobates Koch, 1837), including the description of four new species and a key to all so far known species.

Four new water mite species of the genus Hygrobates, subgenus Lurchibates (Acari, Hydrachnidia, Hygrobatidae) are described. Hygrobates (Lurchibates) macrochela sp. nov. Goldschmidt, Nishikawa Shimano is described in male and female; Hygrobates (Lurchibates) malosimilis sp. nov. Goldschmidt, Nishikawa Shimano is described in male, both new water mite species were collected from newts of the species Pachytriton inexpectatus Nishikawa, Jiang, Matsui Mo, 2011; Hygrobates (Lurchibates) incognitus sp. nov. Goldschmidt, Nishikawa Shimano is described in female collected from newts of the species Paramesotriton guangxiensis (Huang, Tang and Tang, 1983); Hygrobates (Lurchibates) fragmentarius sp. nov. Goldschmidt, Nishikawa Shimano is described in a single severely fragmented specimen (sex could not be determined) collected from a newt of the species Paramesotriton yunwuensis Wu, Jiang, and Hanken, 2010. Principal differences between the subgenus Lurchibates and the nominal subgenus Hygrobates s. str. are illustrated and discussed as well as the sexual dimorphism of Lurchibates. Morphometric analyses confirmed the morphological differences of ten out of the eleven so far described species (H. (L.) fragmentarius could not be included in the analysis); two morphological groups became evident mainly based upon the shape of the anterior coxae. These analyses as well provide an idea of possible phylogenetic relationships among the species. A key to all currently known species of the subgenus Lurchibates is given. So far the subgenus is restricted to SE-Asia, a map showing the distribution of all species is presented.

Multiple newt threats – occurrence of Paramesotriton deloustali and P. guangxiensis in differently disturbed habitats in Vietnam including new data on the parasite-host relationships with water mites

In this study we present the results from field work in northern Vietnam regarding the occurrence of the warty newt species Paramesotriton deloustali and P. guangxiensis in disturbed and undisturbed habitats and the presence of parasitic water mites of the genus Hygrobates (sg. Lurchibates) (Acari, Hydrachnidia). We report the first evidence of mite parasitism in P. guangxiensis and analyze differences in the infestation rates between both Paramesotriton species and habitat qualities. Furthermore we present the first indication of the detrimental effects of these parasite-host interactions.Our preliminary assessment seems to support the sensitivity of P. guangxiensis to habitat disturbances, as the average number of captured newts per stream was twice as high in undisturbed habitats as in disturbed ones.Until now a very specific parasite-host association was supposed between water mite and newt species. However, our results show the first evidence of a water mite species of the subgenus Lurchibates (Hygrobates forcipifer) parasitizing more than one host species, in this case not only P. deloustali (already known) but also P. guangxiensis (new record). The overall infestation rate was 27 % for P. deloustali and 71 % for P. guangxiensis, from which 100 % and 77 % of the mite-incidence occurred in undisturbed habitats, respectively. Furthermore the parasite load of the newts was clearly higher in prime quality streams: the parasite load in undisturbed habitats was very similar between P. deloustali (19.64 mites per newt) and P. guangxiensis (20.13 mites per newt), however it was significantly lower for P. guangxiensis in disturbed habitats (8.86 mites per newt). Future research should bring more detail on these parasite host associations, especially on the effect of parasitism on the newts. Warty newts are already threatened due to their shrinking natural habitat and overharvesting. We report the first concerns that mite parasitism might be a critical additional stress factor in undisturbed habitats.

Phylogenetically conserved host traits and local abiotic conditions jointly drive the geography of parasite intensity

Abstract The role of biotic interactions in shaping species distributions is a cornerstone of biogeographic theory; yet, it remains elusive. Such interactions are more likely to have an influence on organisms with obligate associations, such as hosts and their parasites. Whereas abiotic conditions may affect the abundance and distribution of parasites in ways similar to free‐living species, attributes of the host could also play a part. Here, we focus on parasitic water mites and their dragonfly and damselfly hosts, and use a hierarchical Bayesian model to examine the relative influence of the abiotic environment and biotic factors such as local host community structure and individual host characteristics on parasite intensity along a broad‐scale environmental gradient. Specifically, we assessed how climate, surrounding vegetation, water chemistry, host community structure as well as the relative abundance and body mass of host species affected the intensity of parasitism on individual hosts along a latitudinal gradient. We found that water chemistry and body mass of the host were the best predictors of variation in parasite intensity among hosts. High parasite intensity was observed in hosts sampled from lakes with high pH, dissolved oxygen and conductivity. Additionally, we found that the intensity of parasitism was strongly influenced by host species identity. In particular, body mass, which shows strong phylogenetic signal, was negatively related to parasite intensity. It may be that larger species, or individuals within species, are more immune to high level of parasitism and/or body mass is correlated with other traits of the host which relate to immunity. Considering both the abiotic environment and attributes of host species is necessary to understand why certain host individuals and locations exhibit more intense parasitism. Amid widespread decline of insect populations world‐wide, some of which are attributed to pathogens and parasites, models predicting rates of parasitism in space and time could become an essential tool for guiding management and conservation efforts. A free Plain Language Summary can be found within the Supporting Information of this article.

Eco-immunology of native and invasive water bugs in response to water mite parasites: insights from phenoloxidase activity

Biological invasions provide an opportunity for ecological and evolutionary exploration of immune function in host–parasite interactions. Studying parasite-induced immune response in native and invasive species can provide novel insights into mechanisms underlying invasion success. We aimed to establish the influence of mite ectoparasites on the invasion of the alien water boatman Trichocorixa verticalis (Corixidae) originating from North America. We examined the variation in a key component of insect immune function (phenoloxidase activity), and condition (fat storage) of T. verticalis and four species of native water boatmen in relation to water mites, combining field and laboratory observations in southern Spain. Mite infection was associated with a general decrease in corixid immune function (but not of fat stores), but to a varying extent in different host species. Immunosuppression was particularly high in the alien species, which also had a particularly high prevalence of mites in both field and laboratory infections. Mite infections may therefore explain the low abundance of the alien corixid in low salinity ponds, where native corixids dominated and mites were abundant. Uninfected T. verticalis had a lower immune function than three native corixid species, probably because the alien is adapted to higher salinities where ectoparasites are absent, supporting the “cost of immunity hypothesis”. This study shows that higher immunocompetence in invasive species is not the rule as previously assumed, and highlights the need to better integrate immunology into invasion biology.

<p class="Body">Parasitism of mosquitoes (Diptera: Culicidae) by water mite larvae (Acari: Hydrachnidia) in Amol, Mazandaran Province, northern Iran

Mosquitoes transmit a wide range of vector-borne diseases to humans and animal. Due to the increase in insecticide resistance, there is a need for novel mosquito vector control programs, including biocontrol. Some water mite larvae, such as those of Arrenurus genus, act as parasites of mosquitoes. Mosquito larvae, pupae and adults were collected from three locations in Amol County, Iran by dipping and hand-catch collection methods, from May to late September 2015. Then mites were removed from mosquitoes and identified to genus level using valid identification keys. A total of 873 adults of anopheline mosquitoes belonging to three species (Anopheles maculipennis s.lat., An. pseudopictus and An. hyrcanus) were collected. We only found Arrenurus sp. mites. From 873 anopheline mosquitoes captured, 11% were parasitized by 151 mites, with a mean rate of 1.59, ranging from 1 to 14. Parasitism was higher in lowlands. Water mites, as biocontrol agents of vectors, could impact fecundity, fertility and induce other harms on host. As this study is the first research on water mite parasitism on mosquitoes in Iran, more detailed studies are needed to increase our knowledge on biology and ecology of water mites parasitizing mosquitoes in Amol and other areas in Caspian sea region in Iran.

Negative covariance between water mite and gregarine parasitism for adult dragonflies, Leucorrhinia intacta (Hagen): an age-related pattern?

Studies on parasite-mediated selection often focus on single parasite taxa infecting single species of hosts. However, host populations experience infections by multiple parasite taxa simultaneously; coinfection is expected to influence how host- and/or parasite-related factors affect host exposure and susceptibility to various parasites, and the resulting patterns of infection. We sampled adult dragonflies from a population of Leucorrhinia intacta (Hagen) in eastern Ontario, Canada. Dragonflies were exposed to parasitism by both water mites (Arrenuridae) and gregarines (Eugregarinidae). We tested for covariation between these ecto- and endoparasites, while considering potential sex and age biases in host sampling and patterns of infection. Mite parasitism differed dramatically between host sexes: nearly all collected males were parasitized, whereas only half of females were infested. This was likely due to differences in age distributions between sexes in sampled dragonflies. Water mite and gregarine parasitism showed strong, negative covariation, and coinfection occurred far less often than expected by chance, although these patterns were restricted to samples of females which, unlike male samples, likely included many old and young dragonflies. We report the first observation of negative covariation between internal and external parasite taxa in an anisopteran host and suggest this relationship between water mites and gregarines may be more widespread among Odonata and perhaps other insects than previously surmised. We advance hypotheses based on host age-parasitism relationships as well as variable parasite-mediated selection to help explain the sex specificity of observed coinfection patterns in our samples.

First Record of Aedes albopictus (Diptera: Culicidae) and Second Record of Aedes japonicus (Diptera: Culicidae) Parasitized by Water Mites (Acari: Hydrachnidiae) in North America.

The primary aim of this study was to determine if the Asian tiger mosquito (Aedes albopictus (Skuse)) (Diptera: Culicidae), that vectors a number of arboviruses, is parasitized by water mites (Acari: Prostigmata: Parasitengonina: Hydrachnidiae). Larval water mite parasitism of adult mosquitoes has been shown to reduce mosquito fecundity and life span in the laboratory, and impact some populations in the field. Water mites have been considered for biocontrol purposes and used to age-grade mosquito populations. Consequently, there is interest in water mite-mosquito associations from public health and integrated pest management perspectives. In 2016, the Pennsylvania Department of Environmental Protection West Nile Virus Control Program examined 146,607 mosquitoes representing 31 species for parasitic mites. Ten mosquitoes representing four species rarely or not previously known to be parasitized by mites were saved from destructive West Nile virus and Zika virus testing. Twelve parasitic mites were identified to the lowest taxonomic level possible. An Asian tiger mosquito and an Asian bush mosquito (Aedes japonicus) (Theobald) were each parasitized by a Parathyas sp. Lundblad (Hydryphantoidea: Hydryphantidae: Euthyadinae) water mite, and are the first and second records of these associations in North America, respectively. Two Culex restuans Theobald (Diptera: Culicidae) mosquitoes parasitized by either a Euthyas sp. Piersig (Hydryphantoidea: Hydryphantidae: Euthyadinae) or a Parathyas sp. water mite are new associations, and a Culex pipiens Linnaeus mosquito parasitized by a Parathyas sp. water mite represents a new record for this association in North America.

Phylogeny affects host's weight, immune response and parasitism in damselflies and dragonflies.

Host–parasite interactions are an intriguing part of ecology, and understanding how hosts are able to withstand parasitic attacks, e.g. by allocating resources to immune defence, is important. Damselflies and dragonflies show a variety of parasitism patterns, but large-scale comparative immune defence studies are rare, and it is difficult to say what the interplay is between their immune defence and parasitism. The aim of this study was to find whether there are differences in immune response between different damselfly and dragonfly species and whether these could explain their levels of gregarine and water mite parasitism. Using an artificial pathogen, a piece of nylon filament, we measured the encapsulation response of 22 different damselfly and dragonfly species and found that (i) there are significant encapsulation differences between species, (ii) body mass has a strong association with encapsulation and parasite prevalences, (iii) body mass shows a strong phylogenetic signal, whereas encapsulation response and gregarine and water mite prevalences show weak signals, and (iv) associations between the traits are affected by phylogeny. We do not know what the relationship is between these four traits, but it seems clear that phylogeny plays a role in determining parasitism levels of damselflies and dragonflies.

Testing the enemy release hypothesis in a native insect species with an expanding range.

The enemy release hypothesis (ERH) predicts that the spread of (invasive) species will be facilitated by release from their enemies as they occupy new areas. However, the ERH is rarely tested on native (non-invasive, long established) species with expanding or shifting ranges. I tested the ERH for a native damselfly (Enallagma clausum) whose range has recently expanded in western Canada, with respect to its water mite and gregarine parasites. Parasitism levels (prevalence and intensity) were also compared between E. clausum and a closely related species, Enallagma boreale, which has long been established in the study region and whose range is not shifting. A total of 1,150 damselflies were collected at three ‘old’ sites for E. clausum in Saskatchewan, and three ‘new’ sites in Alberta. A little more than a quarter of the damselflies collected were parasitized with, on average, 18 water mite individuals, and 20% were parasitized by, on average, 10 gregarine individuals. I assessed whether the differences between levels of infection (prevalence and intensity) were due to site type or host species. The ERH was not supported: Enallagma clausum has higher or the same levels of parasitism in new sites than old sites. However, E. boreale seems to be benefitting from the recent range expansion of a native, closely related species through ecological release from its parasites because the parasites may be choosing to infest the novel, potentially naïve, host instead of the well-established host.

Regionally widespread parasitic water mites have relatively broad host-species ranges

Certain parasite species have free-living stages, so habitat range may influence host-species range. We tested whether regional occurrence and habitat use of parasitic water mites were related to their host-species range. We collected 7445 Arrenurus Dugès, 1834 mites from 7107 coenagrionid damselflies, representing 11 host species from 13 sites in southeastern Ontario and southwestern Quebec. Because larval water mites are difficult to identify morphologically to species, we chose to amplify the barcode fragment of cytochrome oxidase subunit I to explore host-species ranges. Fifteen operational taxonomic units or clades were identified based on the amplification from 217 larval mites. The Arrenurus clades that were present in both bog and marsh habitats had a broader host-species range than clades found only in marshes (the comparison with one clade found only in bogs lacked statistical power). As predicted, host-species range increased with the regional occurrence of an Arrenurus clade. Additionally, the most commonly barcoded species also have high host-species ranges. This result could be because species with broader host-species ranges are more common and were more likely to be sampled and barcoded (an explanation we favor), or due to sampling bias. Although this is the first study exploring whether habitat range affects host-species range, further investigation is needed to tease apart which habitat factors influence host-species ranges the most.

Are sexes equally parasitized in damselflies and dragonflies?

Parasitism plays an essential part in ecology and evolution of host species and understanding the reasons for differential parasitism within and among hosts species is therefore important. Among the very important factors potentially affecting parasitism is the gender of the host. Here, we studied whether either females or males are more likely to harbour parasites among Odonatan insects, by relying on an extensive literature review and new field data. We collected data on numerous dragonfly and damselfly species and their ectoparasites (water mites) and endoparasites (gregarines) to examine the generality of similarities and differences in prevalence, intensity and maximum number of parasites of male and female hosts. We found three main results. Firstly, most of the odonate host species showed no differences between sexes in either gregarine or water mite prevalence and intensity. The only exception was female damselflies’ higher gregarine prevalence and intensity compared to conspecific males. These inequalities in gregarine parasitism may be due to behavioral and physiological differences between conspecific males and females. In comparison, there were no differences in dragonflies between sexes in water mite or gregarine prevalence and intensity. Secondly, damselflies had higher prevalence and intensity levels of both gregarine and water mite parasites compared to dragonflies. Finally, we found a strong species level pattern between female and male parasitism: a certain level of gregarine or water mite parasitism in one sex was matched with a similar parasitism level for the other. This indicates similar exposure and susceptibility to parasites on both sexes. Even though significant differences of parasite levels between the sexes were observed within certain host species, our results strongly suggest that on a general level a more parasitized sex does not exist in the order, Odonata.

Differential water mite parasitism, phenoloxidase activity, and resistance to mites are unrelated across pairs of related damselfly species.

Related host species often demonstrate differences in prevalence and/or intensity of infection by particular parasite species, as well as different levels of resistance to those parasites. The mechanisms underlying this interspecific variation in parasitism and resistance expression are not well understood. Surprisingly, few researchers have assessed relations between actual levels of parasitism and resistance to parasites seen in nature across multiple host species. The main goal of this study was to determine whether interspecific variation in resistance against ectoparasitic larval water mites either was predictive of interspecific variation in parasitism for ten closely related species of damselflies (grouped into five “species pairs”), or was predicted by interspecific variation in a commonly used measure of innate immunity (total Phenoloxidase or potential PO activity). Two of five species pairs had interspecific differences in proportions of individuals resisting larval Arrenurus water mites, only one of five species pairs had species differences in prevalence of larval Arrenurus water mites, and another two of five species pairs showed species differences in mean PO activity. Within the two species pairs where species differed in proportion of individuals resisting mites the species with the higher proportion did not have correspondingly higher PO activity levels. Furthermore, the proportion of individuals resisting mites mirrored prevalence of parasitism in only one species pair. There was no interspecific variation in median intensity of mite infestation within any species pair. We conclude that a species’ relative ability to resist particular parasites does not explain interspecific variation in parasitism within species pairs and that neither resistance nor parasitism is reflected by interspecific variation in total PO or potential PO activity.

Populations of the damselflyCoenagrion hastulatumat the edge of the species range have fewer gregarine and water mite parasites

SummaryThe metapopulation theory predicts that the more distant a host population is from other populations, the more challenged will be a parasite to colonise it. We studied parasite prevalence of two parasite taxa across the geographical range of their host in Finland, from more dense host population structure in the south of Finland, towards the northern edge of the host distribution characterised by more isolated populations.We found that prevalence of both water mites and gregarines decreased with increasing latitude towards the distribution edge with more isolated population structure of the host damselfly,Coenagrion hastulatum. Furthermore, the prevalences of the two parasite groups were positively correlated.The results are discussed in the context of three non‐mutually exclusive hypotheses, explaining why host species have fewer parasites at the edge of their geographic range: (i) unsuitable host hypothesis, (ii) physiological barrier hypothesis and (iii) metapopulation hypothesis.

First record of parasitism of water mite larva (Acari: Hydrachnidia) on the pupa of Trichoptera.

During the studies on ecology of Trichoptera of anthropogenic water bodies we have unexpectedly discovered the parasitic larvae of water mites of the species Tiphys torris on the pupa of Triaenodes bicolor. This is the first documented case of the parasitism of water mites on the caddisfly pupa as well as the first ever record of the species which is regarded as a dipteran parasite on caddisflies. The situation is very untypical for preimaginal stages of caddisflies are used by phoretic and not parasitic water mite larvae. Parasitism has been confirmed in this case by the formation of stylostomes and enlarged sizes of the bodies of the larvae. This is probably the case of facultative parasitism in which the pupa has served as a substitute of the adult form of a caddisfly.

Comparing Natural Parasitism and Resistance with Proxies of Host Immune Response in Lestid Damselflies

Commonly used proxies for measuring immune responses in invertebrates include the amount of melanin deposited on nylon inserts and assays of activity of the enzyme phenoloxidase (PO) in the haemolymph. We used these proxies to estimate immunity in unpar- asitized individuals from four Lestid damselfly species from popula- tions with different levels of water mite parasitism. Levels of para- sitism and resistance by hosts were population level estimates from published papers. These parasitism levels were not correlated posi- tively with immune response measured by proxies in the current study. The species with the strongest melanization response to the inserts and the highest PO levels was the one that currently experienced no mite parasitism. The species with the weakest response to the inserts and the lowest PO levels had low current levels of parasitism. The two species that are heavily parasitized had an intermediate response. Natural resistance levels were also not correlated with the response measured by proxies, but the species with a strong response had high levels of resistance in the past. This finding is supported by earlier work done with Lepidoptera in which the most well-defended species currently experience no natural parasitism.