Parasitism ofAcyrthosiphon pisum byAllothrombium pulvinum (Acariformes: Trombidiidae): Host attachment site,host size selection,superparasitism and effect on host

Several aspects of parasitism of the pea aphid,Acyrthosiphon pisum (Harris), by the mite parasiteAllothrombium pulvinum Ewing, were examined in the laboratory. Larvae ofA. pulvinum were fastmoving mites that find their host by contact of their foretarsi with the host. They can attach to all parts of the host body, but insert their chelicerae only into weakly sclerotized parts such as intersegmental membranes. Of the attached larval mites, most (63.5–74.1%) were on the thorax of their hosts, regardless of host size. In hosts of small and medium size, the ventral side receives most parasitism, whereas in large hosts the lateral sites are most often attacked. Larval mites prefer large hosts when allowed to select between pairs of large and small hosts, but show no significant preference when allowed to choose between pairs of large and medium hosts or pairs of medium and small hosts. In two-choice tests, larval mites prefer previously parasitized hosts to umparasitized hosts, which results in superparasitism of the hosts. When the mite load is fiveA. pulvinum kills all small hosts within three days, and all medium hosts and 50% of large hosts within four days, the reproduction of surviving adult aphids were significantly reduced. Host-finding behavior, attachment site preference, host size selection, superparasitism, and effect on hosts are briefly reviewed for larval parasites of Trombidiidae. The potential role of larvalAllothrombium in integrated and biological aphid control is also discussed.     

Water mite parasitism in damselflies during emergence: two hosts, one pattern

The infections of emerging damselfly cohorts by ectoparasitic water mites Arrenurus cuspidator were followed closely over two years in two populations. In one pond Coenagrion puella was the single host species, whereas in the second pond C. hastulatum co-occurred. The prevalences found were close to 100%. The mean daily abundance of mites ranged from I to 45 mites per host with a peak after roughly one third of the emergence period.
The water mites displayed a clumped distribution on their hosts measured by the variance/mean ratio. No differences in parasite abundance due to host sex, head width, or host species could be detected. The abundance of mites was synchronised with host's emergence patterns. This was stronger in the system with two host species. Shaw and Dobson recently showed a generalised relationship of variance/mean of parasite abundance combining data from 269 host parasite systems. The data presented here and some other water mite associations show a significant deviation from this general rule.     

Parasite-host associations and life cycles of spring-living water mites (Hydrachnidia, Acari) from Luxembourg

Larval water mites are parasites of various insect species. The main aim of the present study was to analyse the host range of spring dwelling water mites. The investigation focuses on seven spring sites in Luxembourg. Some 24 water mite species were recorded either from the benthos or as parasites attached to flying insects captured in emergence traps. For 20 mite species 35 host species from four Nematocera (Diptera) families were recorded. About 80% of the host species and over 90% of the host individuals were Chironomidae, the others were Limoniidae, Dixidae and Simuliidae. For all water mite species recorded we present the observed host spectrum and/or potential hosts as well as the intensity of parasitism and the phenology of the mites. For 10 mite species the hosts were previously unknown. For another ten species the known host spectrum can be confirmed and extended. The host spectrum ranged from one host species (e.g. for Sperchon insignis) to at least 10 host species (for Sperchon thienemanni, Ljania bipapillata), but the effective host range could not be definitively estimated due to the lack of corresponding data. The hypothesised host preference of the water mites, of which most are strictly confined to spring habitats, for similarly spring-preferring hosts could not be proven. The mean intensity of parasitism was highest for Thyas palustris (10.8 larvae/host) and lowest for Sperchon insignis and Hygrobates norvegicus (1.2 larvae per host for each). The hydryphantid mite Thyas palustris occurred at maximal intensity (41 larvae per host) and the two abdominal parasites Ljania bipapillata and Arrenurus fontinalis showed higher mean intensities than the thoracic parasites did. Larval water mites parasitising chironomids did not exhibit a preference for host sex. The phenology of the larval mite species was varied, some species were only present in samples early in the year and others exclusively in the summer. Another species showed two peaks of occurrence, springtime/early summer and late summer/autumn. In conclusion, the water mite larvae in the studied springs showed differences in host spectra and phenology but there are no clear evidences in both for host partitioning. Maybe, the relative low species diversity of water mites in individual springs and the low inter-specific competition for suitable hosts in combination with the high host abundances and species richness makes springs such favourable habitats for the mites.     

Parasite in peril? A new species of mite in the genus Ophiomegistus Banks (Parasitiformes: Paramegistidae) on an endangered host,the pygmy bluetongue lizard Tiliqua adelaidensis (Peters) (Squamata: Scincidae)

Host‐parasite relationships are generally understudied in wild populations but have a potential to influence host population dynamics and the broader ecosystem, which becomes particularly important when the host is endangered. Herein we describe a new species of parasitic mite from the genus Ophiomegistus (Parasitiformes: Mesostigmata: Paramegistidae) of an endangered South Australian skink; the pygmy bluetongue lizard (Tiliqua adelaidensis). Adult mites were observed on lizard hosts in three different host populations, among which prevalence varied. No temporal trend in prevalence was evident over two spring‐summer seasons of monitoring. We hypothesise that the reliance on burrows as refuges by T. adelaidensis may be essential for the completion of the mite life cycle and also for horizontal transmission. The conservation implications of not only its effect on the host, but also its potential status as an endangered species itself, are considered.     

Parasitism ofAphis gossypii (Homoptera: Aphididae) byAllothrombium pulvinum larvae (Acari: Trombidiidae) in cotton fields: spatial dispersion and density dependence

Spatial aspects of the interaction between the aphid host,Aphis gossypii, and its parasite,Allo-thrombium pulvinum larvae, on cotton plants were examined in seven fields in China. For both the host and the parasite, sample variance increased with the mean according to Taylor's power law, which explained a substantial proportion (84–97%) of the variation in the data. Although both the host and parasite showed aggregated distribution on cotton plants, the host aphids aggregated more strongly than the parasites. The host dispersion pattern was not significantly affected by the presence of parasites. Increasing the spatial scales of observation from individual plot to the entire field also had no significant effects on host and parasite dispersion patterns. Parasites aggregated in cotton plants with higher aphid densities in five out of the seventeen samples. Spatial patterns of parasitism were mostly host density-independent (71% of the samples) and sometimes inversely density-dependent (29% of the sample). The processes underlying these patterns were discussed.     

Behaviours of phoretic mites (Acari) associated with Ips pini and Ips grandicollis (Coleoptera: Curculionidae) during host‐tree colonization

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Symbionts of societies that fission: mites as guests or parasites of army ants

• 1 Recently, Hughes et al. (Trends in Ecology & Evolution, 23 , 672–677, 2008) have theorised that symbionts of large, long‐lived, homeostatic, and well defended social insect colonies should mostly be of low virulence. If the symbionts are rare, i.e. few workers are co‐infected, competition between symbionts should be minimal and they should be selected to avoid over‐exploiting their hosts.
• 2 Here we analyse the mites that occur on Eciton burchellii army ant workers and note that our findings are consistent with the predictions from evolutionary theory.
• 3 The mites were species diverse but rare; only 5% of the 3146 workers we examined from 20 army ant colonies had mites. Only one worker was co‐infected by mites of different species and the one relatively common parasitic mite (Rettenmeyerius carli) was limited to only two individuals per ant.
• 4 We also showed that certain mites are more common on workers in nomadic rather than statary army ant colonies and that different worker castes differed in their infestation patterns.
• 5 We suggest that the three traits E. burchellii and honey bees (Apis mellifera) have in common (queens with very high mating frequencies, propagation by colony fission, and low number of parasites among the mite species they host) are associated with one another. Colonies that fission are likely to inherit symbionts and multiple mating will promote genetic diversity within colonies, which may help to limit the abundance of deleterious mites.
• 6 We conclude that most of the symbiotic mites found on workers of the army ant E. burchellii are probably relatively harmless guests, exploiting their hosts for phoresis or, for example, to use their waste deposits.

     

Mite‐y bees: bumble bees (Bombus spp., Hymenoptera: Apidae) host a relatively homogeneous mite (Acari) community,shaped by bee species identity but not by geographic proximity

1. Parasites can affect the communities of their hosts; and hosts, in turn, shape communities of parasites and other symbionts. This makes host–symbiont relationships a key but often overlooked aspect of community ecology. 2. Mites associated with bees have a range of lifestyles; however, little is known about mites associated with wild bees or about factors influencing the make‐up of bee‐associated mite communities. This study investigated how mite communities associated with bumble bees (Bombus spp.) are shaped by the Bombus community and geographic proximity. 3. Bees were collected from 15 sites in Ontario, Canada, and examined for mites. Mite abundance and species richness increased with local bee abundance. Several bee species also differed in mite abundance, species richness, prevalence, and diversity. Locally uncommon species tended to have more mites than other bees. Queen bees had the most mites, and males had more mites than workers. 4. Spatial proximity was not a predictor of mite community composition, despite a strong effect of proximity on bee community similarity. 5. On the 11 Bombus spp. examined, 33 mite species were found. Whereas nearly half of these mite species are obligate associates of bumble bees, none was restricted to particular Bombus species. 6. The best predictor of mite community composition was bee identity. Although many parasite communities show strong geographic patterns, the communities of primarily commensalistic bee‐mites in this study did not. These findings have implications for bumble bee conservation, given that pollen‐feeding commensals might become harmful at high densities or act as disease vectors.     

Host sex preferences and transmission success by the water mite Unionicola foili (Acari: Unionicolidae) parasitic on the midge Chironomus tentans (Diptera: Chironomidae)

This study examined whether ecoparasitic larval Unionicola foili exhibited a sex bias when infecting laboratory populations of the host insect Chironomus tentans and whether an association with male or female midges increased the likelihood of larval mites returning to the aquatic habitat. When laboratory populations of C. tentans were exposed to larval U. foili, there was a higher prevalence of mites among female hosts at emergence (17 of 30 males vs. 25 of 30 females infected by mites). However, there was no significant difference in the distribution or abundance of larvae among infected male (mean = 2.3 larvae per host) and female (mean = 2.6 larvae per host) midges. Larval mites parasitizing both male and female chironomids were more likely to return to water than could be expected by chance. Mite larvae infesting female C. tentans were more likely to return to water when female hosts deposited egg masses in water, suggesting that oviposition plays an important role in cueing larvae parasitizing female midges to detach. The mechanism responsible for increasing the likelihood that mites parasitizing male hosts return to water remains unclear. Future studies will address the possibility of parasite-mediated changes in host behavior.     

Seasonal and spatial dynamics of ectoparasite infestation of a threatened reptile, the tuatara (Sphenodon punctatus)

Abstract The conservation of threatened vertebrate species and their threatened parasites requires an understanding of the factors influencing their distribution and dynamics. This is particularly important for species maintained in conservation reserves at high densities, where increased contact among hosts could lead to increased rates of parasitism. The tuatara (Sphenodon punctatus) (Reptilia: Sphenodontia) is a threatened reptile that persists at high densities in forests (～ 2700 tuatara/ha) and lower densities in pastures and shrubland (< 200 tuatara/ha) on Stephens Island, New Zealand. We investigated the lifecycles and seasonal dynamics of infestation of two ectoparasites (the tuatara tick, Amblyomma sphenodonti, and trombiculid mites, Neotrombicula sp.) in a mark‐recapture study in three forest study plots from November 2004 to March 2007, and compared infestation levels among habitat types in March 2006. Tick loads were lowest over summer and peaked from late autumn (May) until early spring (September). Mating and engorgement of female ticks was highest over spring, and larval tick loads subsequently increased in early autumn (March). Nymphal tick loads increased in September, and adult tick loads increased in May. Our findings suggest the tuatara tick has a 2‐ or 3‐year lifecycle. Mite loads were highest over summer and autumn, and peaked in March. Prevalences (proportion of hosts infected) and densities (estimated number of parasites per hectare) of ticks were similar among habitats, but tick loads (parasites per host) were higher in pastures than in forests and shrub. The prevalence and density of mites was higher in forests than in pasture or shrub, but mite loads were similar among habitats. We suggest that a higher density of tuatara in forests may reduce the ectoparasite loads of individuals through a dilution effect. Understanding host–parasite dynamics will help in the conservation management of both the host and its parasites.     

The effect of population density on the reproduction ofTrichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae)

When a fixed number of the hosts, the eggs of the almond moth were exposed experimentally to various numbers of the parasites, Trichogramma japonicum, the following changes were observed with increasing parasite density:

1. The percentage of parasitism rises and approaches to 100 with gradually diminishing rate.
2. The number of parasite progeny increases and reaches a maximum, then decreases gradually.
3. The number of eggs laid per parasite female decreases gradually.
4. The proportion of hyperparasitized hosts progressively rises. The frequency distribution of parasite eggs in a host is of an intermediate type between random and uniform.
5. The competition among parasite larvae becomes severe. The progressive rise in mortality, the declining percentage of females in progeny and the emergence of stunted adults at the higher densities are observed.

In connection with both the nature of the parasitizing behaviour of adult and that of the competition among larvae, the nature of the density effect on the parasite population was discussed.     

The influence of parasitic water mites on the instantaneous death rate of their hosts

Summary The effect of 2 species of water mites on the instantaneous death rate of their hosts was measured on the basis of laboratory experiments. In both parasite-host association — the parasitic water mite Hydryphantes tenuabilis on the aquatic insect host Hydrometra australis and the parasitic water mite Arrenurus pseudotenuicollis on the mosquito Anopheles crucians — the effect of mite load on the instantaneous death rate of the host appeared to be linear. Also, the impact of a single parasite on the host's death rate was apparently related to the ratio of parasite to host body weight. The results of this study are in general agreement with recent theoretical investigations of the regulation of host populations by parasites.     

A link between host dispersal and parasite diversity in two sympatric cichlids of Lake Tanganyika

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Regulatory processes and population cyclicity in laboratory populations ofAnagasta kühniella (Zeller) (lepidoptera: Phycitidae) V. Host finding and parasitization in a “small” universe by an entomophagous parasite,Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae)

Summary Host finding by the entomophagous parasite,Venturia canescens (Grav.), parasitizingAnagasta kühniella (Zeller) was studied. Studies utilizing fixed densities and dispersion patterns of the hosts where no choice of density groupings was offered showed that within the experimental conditions used, host density relationships were more important than dispersion. Decreasing the time hosts were exposed to a parasite from 72 hours to 24 hours did not alter the overall parasitization. In both cases progressively less hosts were parasitized as host density increased, which exemplified aHolling-type of response. However, when host densities were varied within the same universe, independent of dispersion patterns, and the parasites were given a “choice” of host densities to attack, an increasing percentage of hosts in the higher host density groups were parasitized; thus a density-dependent behavioral response was exhibited. These studies were conducted as a partial fulfillment in the Ph. D. program of one of us (B. M. Matsumoto) and form a part of a broad investigation into the processes operating in the dynamics of arthropod populations under grants toC. B. Huffaker from the U. S. Public Health Service, National Institutes of Health and the U. S. Department of Agriculture.     

Adaptive population structure shifts in invasive parasitic mites,Varroa destructor

Comparative studies of genetic diversity and population structure can shed light on the ecological and evolutionary factors governing host–parasite interactions. Even though invasive parasites are considered of major biological importance, little is known about their adaptative potential when infesting the new hosts. Here, the genetic diversification of Varroa destructor, a novel parasite of Apis mellifera originating from Asia, was investigated using population genetics to determine how the genetic structure of the parasite changed in distinct European populations of its new host. To do so, mites infesting two categories of hosts in four European regions were compared: (a) adapted hosts surviving through means of natural selection, thereby expected to impose strong selective pressure on the mites, and (b) treated host populations, surviving mite infestations because acaricides are applied, therefore characterized by a relaxed selection imposed by the host on the mites. Significant genetic divergence was found across regions, partially reflecting the invasion pattern of V. destructor throughout Europe and indicating local adaptation of the mite to the host populations. Additionally, varying degrees of genotypic changes were found between mites from adapted and treated colonies. Altogether, these results indicate that V. destructor managed to overcome the genetic bottlenecks following its introduction in Europe and that host‐mediated selection fostered changes in the genetic structure of this mite at diverse geographic scales. These findings highlight the potential of parasites to adapt to their local host populations and confirm that adaptations developed within coevolutionary dynamics are a major determinant of population genetic changes.     

Cophylogenetic assessment of New World warblers (Parulidae) and their symbiotic feather mites (Proctophyllodidae)

Host–symbiont relationships are ubiquitous in nature, yet evolutionary and ecological processes that shape these intricate associations are often poorly understood. All orders of birds engage in symbioses with feather mites, which are ectosymbiotic arthropods that spend their entire life on hosts. Due to their permanent obligatory association with hosts, limited dispersal and primarily vertical transmission, we hypothesized that the cospeciation between feather mites and hosts within one avian family (Parulidae) would be perfect (strict cospeciation). We assessed cophylogenetic patterns and tested for congruence between species in two confamiliar feather mite genera (Proctophyllodidae: Proctophyllodes, Amerodectes) found on 13 species of migratory warblers (and one other closely related migratory species) in the eastern United States. Based on COI sequence data, we found three Proctophyllodes lineages and six Amerodectes lineages. Distance‐ and event‐based cophylogenetic analyses suggested different cophylogenetic trajectories of the two mite genera, and although some associations were significant, there was little overall evidence supporting strict cospeciation. Host switching is likely responsible for incongruent phylogenies. In one case, we documented prairie warblers Setophaga discolor harboring two mite species of the same genus. Most interestingly, we found strong evidence that host ecology may influence the likelihood of host switching occurring. For example, we documented relatively distantly related ground‐nesting hosts (ovenbird Seiurus aurocapilla and Kentucky warbler Geothlypis formosa) sharing a single mite species, while other birds are shrub/canopy or cavity nesters. Overall, our results suggest that cospeciation is not the case for feather mites and parulid hosts at this fine phylogenetic scale, and raise the question if cospeciation applies for other symbiotic systems involving hosts that have complex life histories. We also provide preliminary evidence that incorporating host ecological traits into cophylogenetic analyses may be useful for understanding how symbiotic systems have evolved.     

Survival and reproductive rate of mites in relation to resistance of their barn swallow hosts

Parasite resistance may act via a number of different mechanisms that regulate or control the survival and the reproductive rate of parasites. Observations and experiments were used to test for effects of host resistance on parasite survival and rate of reproduction. Natural levels of infestation of barn swallow Hirundo rustica nests by the tropical fowl mite Ornithonyssus bursa were positively related to brood size, inversely related to the length of the outermost tail feathers of male nest owners (a secondary sexual character) and affected by time of reproduction by the host. A mite inoculation experiment, in which 50 adult mites were introduced into nests during the laying period of the host, was used to test for differential survival and reproduction of mites as a function of host resistance. The relationship between survival and reproduction of parasites, male tail length and host resistance was investigated. There was a negative relationship between mite numbers per nest after fledging of nestlings and male tail length. This relationship was mainly caused by a reduction in the number of mites in the first and second nymph stage with increasing tail length of male hosts, implying a reduction in rate of reproduction of mites. The proportion of mites that had recently fed was inversely related to tail length of male hosts. The proportion of nymph stages was positively related to the proportion of mites that had recently had a blood meal. Parasite resistance of barn swallows to the tropical fowl mite thus appeared to act through increased mortality rate of adult and nymph stages of mites, and through reduced reproductive rates of mites on resistant hosts. This is the first study demonstating a direct relationship between fitness components of a parasite and the expression of a secondary sexual character of a host. Received: 11 January 2000 / Accepted: 22 March 2000     

Host-seeking behaviour of tracheal mites (Acari: Tarsonemidae) on honey bees (Hymenoptera: Apidae)

The behaviour of the endoparasitic tracheal mite, Acarapis woodi (Rennie) on honey bees (Apis mellifera L.) is a challenge to observe because of its small size. Through a microscope, we videotaped this mite's movement on young bees, dead bees and bees exposed to vegetable oil. Previous studies have shown that solid vegetable oil decreases mite infestations in a bee colony. We hypothesized that the oil alters mite behaviour to the detriment of the parasite, thus helping to safeguard the host. Habitat-seeking behaviour, identified as necessary for mites to locate a new host environment, was disrupted on both dead and oil-treated bees. Questing behaviour, which is associated with transfer between hosts, increased significantly on the dead and oily bees. The behaviours of mites were significantly different between all three treatments (x ²=494.96, p<0.001 on dead bees and x ²=851.11, p<0.001 on oily bees). Both questing and seeking behaviours were significantly different on each of the thoracic treatments (F _2,66=7.88, p<0.001 and F _2,66=21.28, p<0.001) and mite questing behaviour was not altered between males and females on live or oily bees (F _1,22=0.25, p<0.62), but habitat seeking was (F _1,22=7.42, p<0.012). The male questing and habitat-seeking behaviours were observed. We conclude that oil-treated bees gained protection from habitat-seeking mites because the normal behaviour of the mites seeking an oviposition site is interrupted.     

Metazoan parasites of African annual killifish (Nothobranchiidae): abundance,diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non‐overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non‐aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts.     

Spatial and temporal variation in recruitment and its effects on regulation of parasite populations

Variation in recruitment rates of parasites to hosts possibly contributes significantly to fluctuations in parasite numbers, yet is almost never measured directly in the field. I measured the variation in recruitment rates of three species of parasitic mites living in two species of freshwater mussels over several spatial and temporal scales. I also examined separately the effect of spatial dispersion of hosts on mite recruitment. Uninfected hosts of both species were placed out each month, for a period of a month, for 2 years at one site and 12 months at another. Mussels of both species were collected simultaneously each month so that abundance of recruiting mites could be compared to mean abundances of mites in hosts at that time. To test the effect of host dispersion on recruitment rates, mussels were set out in clumped and regular patterns in a separate experiment. Overall, recruitment rates were often high but also varied substantially between sites, seasons, years and months. The likely impacts differed between mite species with one probably affected strongly by recruitment variation, while abundances of the other two were not. Populations of the latter two species are probably regulated by intraspecific competition for mates and egg-laying sites. Sampling data are often used to estimate recruitment rates but the latter should be measured, if possible, by exposing uninfected hosts for a known period of time. This direct method reveals patterns of recruitment that cannot be deduced from sampling data. The lack of information on recruitment variation represents a major gap in our knowledge of parasite populations.