恙螨杂交的研究

本文报道了在实验室内对微红纤恙螨和地里纤恙螨进行杂交试验,再次征明这两种恙螨不容易杂交,偶然条交后其繁殖率与成活率比纯种配对的低得多.从F₁繁殖至F₂更困难,而且F₂的成活率更低,说明两者有生殖隔离现象.杂交子代的背板测量数据和幼虫体色出现中间类型,少数个体出现畸形和背毛变异等.以上异常现象在实验室纯种繁殖多代中极少见到.这一切为研究恙螨的种型和正确对待庞大的纤恙螨亚属中幼虫的分类具有重要意义.     

Extra-oral digestion and the problem of parasitism in Parasitengona mites (Acariformes)

An analysis of the extra-oral digestion in Parasitengona being a highly specialized group of Acariform mites is carried out from the viewpoint of functional morphology and ecology. The significance of the extra-oral digestion in the life strategy of these mites and their larval parasitism is also evaluated. The morphological pre-adaptations of this mode of feeding as well as its probable evolutionary consequences are demonstrated by an example of trombiculid mites (Trombiculidae). It is shown, in particular, that parasitism in general may be considered as a particular life scenario implying that the feeding preferences of the organism are evolutionary formed in a close association with other organisms, which provide a parasite with a feeding substrate mainly already prepared for utilization. Based on this assumption, all Parasitengona, including both larval and post-larval instars, irrespectively of the size of their potential victim, preferably should not be considered as parasites, but as micro-predators.     

Morphology of Parasitengona mites (Acariformes: Parasitengona) and their possible evolutionary scenario

On the basis of the analysis of morphology and biology of representatives of the Parasitengona, mostly trombiculids, trombidiids and water mites, a new attempt is made to clarify probable evolutionary scenario in this group of the higher trombidiform mites (Actinedida). It is supposed that the very old ancestral group of terrestrial arachnids, having bite-sucking mouth-parts, poorly differentiated sac-like midgut and capability to extra-oral digestion, fed predatory on different small soil arthropods at all phases of the life cycle. They were small segmented orthotrichous homeomorphic arachnids at the rank of genus or family. The favorable feeding conditions of the adult phase have led to the small eggs rich in yolk and the small larva. The latter have led in turn to the necessity of intensive feeding at the larval stage to complete the ontogenesis. Further in evolution, this group gave rise at once to two or even more large paraphyletic branches. Most of them retained feeding on arthropods with transition of larvae to much more effective parasitic feeding provided with the additional specialization of the larval stage. This branch comprise divergently radiated paraphyletic terrestrial and secondary-water water mites each having long course of evolution resulted in the recent groups of Calyptostomatoidea, Erythraeoidea, Trombidioidea and several superfamilies of water mites. Another branch of the ancestral Parasitengona has followed the way of adaptation of larvae to feeding on vertebrates, which were being attacked by the larvae in the environment of pasture. The parasitism on vertebrates has lead to several radical specializations of these mites and their significant evolutionary progress. At the same time, the similar ontogenetic dynamics, as well as synchronous reduction of particular developmental stages in all parasitengones, inevitably indicate the monophyletic origin of the whole branch of Parasitengona with Pterygosomatidae as the most probable sister group.     

The origin and evolution of parasitism on terrestrial vertebrates in insects, mites, and ticks

Coexistence of terrestrial vertebrates and arthropods has been continuing over 200 million years; various forms of parasitism originated independently in various groups of arthropods during this period. The association of Acari and insects with nests and shelters of their hosts (nidicoly) played the main role in the origin of parasitism in these major groups of arthropods. The primary step in the evolution of parasitism was the permanent habitation in nests and borrows of mammals and birds in Mesozoic era. The second step was a substitution of various forms of schizophagy by the regular feeding on products of vital activity and dead parts of host body. The next step was the feeding on various body parts of vertebrate hosts, namely skin, hair, feathers, external excreta, and drops of blood. The final step was the development of the ability to damage skin and suck out the blood of vertebrates. In some taxa of astigmatid mites the parasitism on birds originated from phoresy: hypopi (heteromorphous deutonymphs) obtained the ability to absorb the liquid nutrients from hair follicles and subcutaneous tissues through the cuticle. The development of haematophagous feeding on mammals in several families of Diptera was the second way of the origin of parasitism. Highly mobile dipterans with the piercing-sucking or licking mouthparts were able to change easily from the accidental puncturing of the host skin or licking of the blood, pus, and mucus to the obligatory haematophagy. The evolution of some arthropod taxa did not went beyond a primary domination of spatial relations, as in many astigmatid mites, or trophic relations in the form of micropredatory, as in the haematophagous Diptera.     

THE PARASITOID,Cotesia flavipes (CAMERON) (HYMENOPTERA: BRACONIDAE), INFLUENCES FOOD CONSUMPTION AND UTILIZATION BY LARVAL Diatraea saccharalis (F.) (LEPIDOPTERA: CRAMBIDAE)

Parasitoids exploit host insects for food and other resources; they alter host development and physiology to optimize conditions to favor parasitoid development. Parasitoids influence their hosts by injecting eggs, along with a variety of substances, including venoms, polydnaviruses, ovarian fluids, and other maternal factors, into hosts. These factors induce profound changes in hosts, such as behavior, metabolism, endocrine events, and immune defense. Because endoparasitoids develop and consume tissues from within their hosts, it is reasonable to suggest that internal parasitization would also influence host food consumption and metabolism. We report on the effects of parasitism by Cotesia flavipes on the food consumption and utilization of its host, Diatraea saccharalis. Cotesia flavipes reduces the host food consumption, but parasitized larvae considered a unit with their parasitoid's attained the same final weight as the nonparasitized larvae. Nutritional indices, midgut activities of carbohydrases, and trypsin of parasitized and nonparasitized D. saccharalis were assessed. Parasitized larvae had reduced relative food consumption, metabolic and growth rates, coupled with higher efficiency for conversion of the digested, but not ingested, food into body mass. Parasitism also affected food flux through the gut and protein contents in the midgut of parasitized larvae. The activity of α‐amylase and trehalase in parasitized host was enhanced in the first day after parasitism relative to control larvae. Saccharase activity remained unchanged during larval development. Trypsin activity was reduced from the fifth to ninth day after parasitism. We argue on the mechanisms involved in host food processing after parasitism.     

Mite pockets of lizards, a possible means of reducing damage by ectoparasites

Many scattered lizard groups have small skin invaginations in such places as the neck, axilla, groin and postfemoral region. These frequently contain feeding chiggers (the larvae of trombiculid mites) which, in general, are much commoner on species with pockets than on those without. Mite pockets appear to have evolved many times, being found in at least five families (Iguanidae, Chamaeleonidae, Gekkonidae, Lacertidae, Scincidae) and are most abundant in warm areas that are not extremely dry. They are present in newly hatched animals and embryos of viviparous forms and so cannot be produced in direct response to the mites. Typically, the epidermis of infested pockets is hyperplastic and resilient, rapidly repairing damage caused by feeding mites, and the dermis contains dense concentrations of lymphoid cells. It is suggested that mite pockets have evolved in forms prone to trombiculid infestation and ameliorate the damage that this causes by concentrating chiggers in places that are equipped to minimize the harm they do.     

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.     

Morphological adaptations of acariform mites (Acari: Acariformes) to permanent parasitism on mammals

The external morphological adaptations to parasitism in acariform mites (Acari: Acariformes), permanently parasiting mammals, are briefly summated and analyzed. According to several external morphological criteria (structures of gnathosoma, idiosoma, setation, legs and life cycle), the following six morphoecotypes were established: skin mites (i)-- Cheyletidae, Chirorhynchobiidae, Lobalgidae, Myobiidae, Myocoptidae (the most part), Rhyncoptidae, Psoroptidae; fur mites (ii)--Atopomelidae, Clirodiscidae, Listrophoridae, Myocoptidae (Trichoecius only); skin burrowing mites (iii)--Sarcoptidae; intradermal mites (iv) - sorergatidae and Demodicidae; interstitial mites (v) - pimyodicidae; respiratory mites (vi) - reynetidae, Gastronyssidae, Lemurnyssidae, Pneumocoptidae. In the case of prostigmatic mites, the detailed reconstruction of the origin and evolution of "parasitic" morphoecotypes is possible due to the tentative phylogenetic hypotheses, which were proposed for the infraorder Eleutherengon, a, including the most part of the permanent mammalian parasites among prostigmatic mites (Kethley in Norton, 1993; Bochkov, 2002). The parasitism of Speleognathinae (Ereynetidae) in the mammalian respiratory tract arose independently of the other prostigmats. It is quite possible that these mites switched on mammals from birds, because they are more widely represented on these hosts than on mammals. The prostigmatic parasitism on mammalian skin seems to be originated independently in myobiids, in the five cheyletid tribes, Cheyletiellini, Niheliini, and Teinocheylini, Chelonotini, Cheyletini, and, probably, in a cheyletoid ansector of the sister families Psorergatidae-Demodicidae (Bochkov, Fain, 2001; Bochkov, 2002). Demodicids and psorergatids developed adaptations to parasitism in the skin gland ducts and directly in the epithelial level, respectively in the process of the subsequent specialization. Mites of the family Epimyodicidae belong to the phylogenetic line independent of other cheyletoids. These mites possess the separate chelicerae and, therefore, can not be included to the superfamily Cheyletoidea. It is not quite clear whether they were skin parasites initially or they directly switched to parasitism from the predation. The phylogeny of sarcoptoid mites (Psoroptidia: Sarcoptoidea) is not developed, however, some hypotheses about origin and the following evolution of their morphoecotypes can be proposed. We belive that astigmatic mites inhabiting the mammalian respiratory tract transferred to parasitism independently of other sarcoptoids. The idiosoma of these mites is not so much flattened dorso-ventrally and has proportions which are similar to hose of free-living astigmatids. Moreover, in the most archaic species, the legs are not shortened or thickened as in the most parasites. The disappearance of many morphological structures in these mites, probably, happened parallely with some other sarcoptoids due to their parasitic mode of life. The skin inhabiting sarcoptoids belong to the "basic" morphoecotype, and all other sarcoptoid morphoecotypes, excluding respiratory mites, are derived from it. Some mites of this morphoecotype live on the concave surfaces of the widened spine-like hairs of the rodents belonging to the family Echimyidae (mites of the subfamily Echimytricalginae), in the mammalian ears (some Psoroptidae) or partially sink into the hair follicles (Rhynocoptidae). Finally, mites of the family Chirorhynchobiidae live on the bat wing edges attaching to them by their "ixodid-like" gnathosoma. The fur-sarcoptoids, probably, originated from the skin mites. This morphoecotype is divided onto two subtypes: mites with the dorso-ventrally flattened idiosoma (subtype I) and mites with the teretial idiosoma (subtype II). Each "fur-mite" family includes mites of the both subtypes. All mites of the first subtype belong to the early derivative lineages in their families. Among listrophorids such early derivative lineage is represented by the subfamily Aplodontochirinae (Bochkov, OConnor, 2006), and among Chirodiscidae--by mites of the subfamilies Chirodiscinae, Schizocoptinae, and Lemuroeciinae. Among the "fur" astigmatid families, the family Atopomelidae. probably, is the most archaic, and the most part of atopomelids belongs to the first subtype. However there are several more specialized atopomelid genera belonging to the second subtype, Atopomelus, Dasyurochirus, Lemuroptes, Murichirus, Metachiroecius etc. We believe that mites of the first subtype are represented by the "intermediate" forms between skin mites and mites of the second subtype. Some skin sarcoptoids transferred from skin parasitism to burrowing of the host skin (Sarcoptidae). The established morphoecotypes are partially corresponding to some morphoecotypes established by Mironov (1987) for feather mites. Our morphoecotypes of skin and skin burrowing mites perfectly correspond to Mironov's epidermoptoid and knemidocoptoid morphoecotypes, respectively. The proctophylloid morphoecotype (mites living on the wing feathers), which is the most widely represented within feather mites, has an analogy among mammalian mites - the subfamily Echimytricalginae. The analgoid (mites living in the down feathers) and dermoglyphoid (mites living in the feather quills) morphoecotypes have no analogues among mammalian mites for the obvious reasons. It is interesting why some microhabitats on the host body are not still occupied by prostigmatic or astigmatic mites. We believe that the nutrition is the main limitative factor here. The parasitic prostigmates evolved from predators and, therefore, feed on content of the living cells. They need the direct contact with the live tissues of the host and they belong, therefore, to the morphoecotypes represented by the respiratory, skin, gland duct, intradermal, and interstitial mites. Whereas, the most part of the skin inhabiting astigmats feed on the dead epithelial scales. For this reason these mites, so easily colonized fur of their hosts and feed on the hair grease there. On the other hand, some sarcoptoids transferred to the true parasitism and feed on the cambial cells of the skin epithelium. More over we do not know exactly about nutrition of rhyncoptids yet.     

Behavioural resistance against a protozoan parasite in the monarch butterfly

1. As parasites can dramatically reduce the fitness of their hosts, there should be strong selection for hosts to evolve and maintain defence mechanisms against their parasites. One way in which hosts may protect themselves against parasitism is through altered behaviours, but such defences have been much less studied than other forms of parasite resistance. 2. We studied whether monarch butterflies (Danaus plexippus L.) use altered behaviours to protect themselves and their offspring against the protozoan parasite Ophryocystis elektroscirrha (McLaughlin & Myers (1970), Journal of Protozoology, 17, p. 300). In particular, we studied whether (i) monarch larvae can avoid contact with infectious parasite spores; (ii) infected larvae preferentially consume therapeutic food plants when given a choice or increase the intake of such plants in the absence of choice; and (iii) infected female butterflies preferentially lay their eggs on medicinal plants that make their offspring less sick. 3. We found that monarch larvae were unable to avoid infectious parasite spores. Larvae were also not able to preferentially feed on therapeutic food plants or increase the ingestion of such plants. However, infected female butterflies preferentially laid their eggs on food plants that reduce parasite growth in their offspring. 4. Our results suggest that animals may use altered behaviours as a protection against parasites and that such behaviours may be limited to a single stage in the host-parasite life cycle. Our results also suggest that animals may use altered behaviours to protect their offspring instead of themselves. Thus, our study indicates that an inclusive fitness approach should be adopted to study behavioural defences against parasites.     

Eukaryotic ectosymbionts of Acari

The Acari is the most numerous and diverse group of the subphylum Chelicerata. With approximately 55 000 described species (and estimates of up to 1 million extant species), their adaptations for parasitism, phytophagy, mycophagy, saprophagy and predation rival other arthropods and challenge us with a wide variety of biological interactions. While a few studies have unravelled the nature of some endosymbiotic associations between mites or ticks and prokaryotes, almost nothing has been done yet regarding acarine eukaryotic ectosymbionts. Microbial ectosymbionts can benefit their hosts by providing nutrients, by aiding digestion, by enhancing communication, by assisting in mating and/or fertilization, by protecting their host against pathogenic microorganisms, against predation and so on. In this sketch, we introduce a number of described cases of fungal and protist ectosymbionts and discuss the role they might play in the life of their acarine hosts.     

Behavioural responses of Varroa destructor (Acari: Varroidae) to extracts of larvae, cocoons and brood food of worker and drone honey bees, Apis mellifera (Hymenoptera: Apidae)

Abstract. Varroa destructor is a parasitic mite of the honey bee species Apis cerana Fabr . and A. mellifera L. Mature females reproduce on the immature stages of their hosts, producing more viable female offspring on drone hosts than on worker hosts. Thus, immature drones are more likely to be infested with mites than immature workers. To investigate the hypothesis that differences in host chemistries underlie the biased distribution of mites between worker and drone brood, the arrestment responses of mites to solvent extracts of a number of stimuli normally encountered by a mite during its life cycle were measured. Mites were arrested by cuticular extracts of worker and drone larvae obtained at 0, 24 and 48 h prior to the time when cell capping is completed. Mites were also arrested by extracts of worker and drone, brood food and cocoons, and by a blend of synthetic fatty acid esters previously shown to be active in the host acquisition process. In a wind tunnel bioassay, mites were attracted to odours from living fifth-instar worker and drone larvae, but not to volatiles from cocoons, brood food or a blend of fatty acid esters. The sex of the host was not an important factor affecting the behavioural responses of the mites in any assay. We conclude that host kairomones play a role in the host acquisition process, but we found no evidence to support the hypothesis that mites use these substances to differentiate between worker and drone brood.     

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.     

Patterns of trombiculid mite (Hannemania dunni) parasitism among plethodontid salamanders in the western Piedmont of North Carolina

Trombiculid mites are known to parasitize a variety of amphibian species, yet few comparisons of mite parasitism among amphibian species have been made. In this study, we investigated patterns of trombiculid mite parasitism among 3 plethodontid salamanders (Desmognathus fuscus, Eurycea cirrigera, and Plethodon cylindraceus) in the western Piedmont of North Carolina. All 3 salamander species were parasitized by a single species, Hannemania dunni. Desmognathus fuscus harbored mites more frequently (60.4% of individuals) than E. cirrigera (11.1%) or P. cylindraceus (14.6%). Desmognathus fuscus also had higher parasite loads than E. cirrigera or P. cylindraceus (P < 0.001). Mites on D. fuscus were found more frequently on the limbs than other body locations (P < 0.001). We found no correlation between salamander size and mite abundance (P = 0.689), but salamander collection sites influenced the abundance of mites on D. fuscus (P = 0.002). We found no effect of season on mite abundance in D. fuscus (P = 0.952). Salamander habitat preferences and edaphic or climatic differences among study sites may influence patterns of Hannemania sp. parasitism of salamanders.     

Success of ectoparasites: how important is timing of host contact?

Hosts often differ in their degree of parasitism and their expression of resistance. Yet very little is known about how the availability (and allocation) of resources to parasites at pre-infective stages influences their success in initiating parasitism, or in inducing and succumbing to resistance from hosts. We studied a damselfly-mite association to address how experimental variation in the age of first contact with hosts (timing) influenced subsequent parasite fitness. We demonstrate that timing influenced the ability of larval mites to make the transition to parasitism, but was not associated with measures of physiological resistance by hosts. Timing presumably relates to the availability of resources remaining for individuals to exploit their hosts. More research is needed on the importance of such factors, from variation in host resistance and parasite success and, ultimately, to the numbers and distributions of parasites on hosts.     

Asynchronous development of honey bee host and Varroa destructor (Mesostigmata: Varroidae) influences reproductive potential of mites

A high proportion of nonreproductive (NR) Varroa destructor Anderson & Trueman (Mesostigmata: Varroidae), is commonly observed in honey bee colonies displaying the varroa sensitive hygienic trait (VSH). This study was conducted to determine the influence of brood removal and subsequent host reinvasion of varroa mites on mite reproduction. We collected foundress mites from stages of brood (newly sealed larvae, prepupae, white-eyed pupae, and pink-eyed pupae) and phoretic mites from adult bees. We then inoculated these mites into cells containing newly sealed larvae. Successful reproduction (foundress laid both a mature male and female) was low (13%) but most common in mites coming from sealed larvae. Unsuccessful reproductive attempts (foundress failed to produce both a mature male and female) were most common in mites from sealed larvae (22%) and prepupae (61%). Lack of any progeny was most common for mites from white-eyed (83%) and pink-eyed pupae (92%). We also collected foundress mites from sealed larvae and transferred them to cells containing newly sealed larvae, prepupae, white-eyed pupae, or pink-eyed pupae. Successful reproduction only occurred in the transfers to sealed larvae (26%). Unsuccessful reproductive attempts were most common in transfers to newly sealed larvae (40%) and to prepupae (25%). Unsuccessful attempts involved the production of immature progeny (60%), the production of only mature daughters (26%) or the production of only a mature male (14%). Generally, lack of progeny was not associated with mites having a lack of stored sperm. Our results suggest that mites exposed to the removal of prepupae or older brood due to hygiene are unlikely to produce viable mites if they invade new hosts soon after brood removal. Asynchrony between the reproductive status of reinvading mites and the developmental stage of their reinvasion hosts may be a primary cause of NR mites in hygienic colonies. Even if reinvading mites use hosts having the proper age for infestation, only a minority of them will reproduce.     

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.     

Recapture of male and female dragonflies in relation to parasitism by mites, time of season, wing length and wing cell symmetry

For aquatic mites parasitic on dragonflies, completion of their life cycle depends on their being returned to appropriate water bodies by their hosts, after completion of engorgement. We examined whether differences among hosts in timing of emergence or phenotypic attributes might affect their probability of return to an emergence pond, and hence success of mites. Parasitized males and females of the dragonfly Sympetrum obtrusum (Hagen) did not differ in overall recapture rates. Females that had wing cell symmetry and emerged early were more likely to be recaptured than females that emerged later or had wing cell asymmetry, but there were no consistent relations between these variables and parasitism by mites. No such relations between wing cell asymmetry, emergence date, and recapture likelihood were found for males. Using randomization tests, we found that mean intensities of Arrenurus planus (Marshall) mites at host emergence were the same for recaptured females and females not recaptured; however, males that were recaptured had lower mean intensities of mites at emergence than males not recaptured. Further, mature females carried more mites than mature males, and the latter had fewer mites than newly emerged males not recaptured. Biases in detachment of engorging mites do not explain the differences in parasitism between mature males and females, nor the differences in mite numbers between mature males and newly emerged males that were not recaptured. Rather, heavily parasitized males appear to disperse or die and are not recaptured, which should have implications for dispersal of mites and fitness of male hosts.     

Neotrombicula autumnalis (Acari, Trombiculidae) as a vector for Borrelia burgdorferi sensu lato?

Larvae of the trombiculid mite Neotrombicula autumnalis were collected at 18 sites in and around Bonn, Germany, to be screened for infection with Borrelia burgdorferi s.l. by means of PCR. Questing larvae numbering 1380 were derived from the vegetation and 634 feeding ones were removed from 100 trapped micromammals including voles, mice, shrews and hedgehogs. In a laboratory infection experiment, a further 305 host-seeking larvae from the field were transferred onto Borrelia-positive mice and gerbils, and examined for spirochete infection at various intervals after repletion. In three cases borrelial DNA could be amplified from the mites: (1) from a larva feeding on a wild-caught greater white-toothed shrew (Crocidura russula), (2) from a pool of four larvae feeding on a B. garinii-positive laboratory mouse, and (3) from a nymph that had fed on a B. afzelii-positive laboratory gerbil as a larva. In the first case, borrelial species determination by DNA hybridization of the PCR product was only possible with a B. burgdorferi complex-specific probe but not with a species-specific one. In the second case, probing showed the same borrelial genospecies (B. garinii) as the laboratory host had been infected with. In the latter case, however, DNA hybridization demonstrated B. valaisiana while the laboratory host had been infected with B. afzelii. Subsequent DNA sequencing confirmed much higher similarity of the PCR product to B. valaisiana than to B. afzelii indicating an infection of the mite prior to feeding on the laboratory host. The negligible percentage of positive mites found in this study suggests that either the uptake of borrelial cells by feeding trombiculids is an extremely rare event or that ingested spirochetes are rapidly digested. On the other hand, the results imply a possible transstadial and transovarial transmission of borreliae once they are established in their trombiculid host. However, unless the transmission of borreliae to a given host is demonstrated, a final statement on the vector competence of trombiculid mites is not possible.     

The endoparasitoid Cotesia kariyai (Ck) regulates the growth and metabolic efficiency of Pseudaletia separata larvae by venom and Ck polydnavirus

It was previously demonstrated that parasitization by Cotesia kariyai caused a decrease in weight gain and food consumption in host larvae, resulting in a lower final weight for parasitized hosts. It is predicted that C. kariyai regulates the physiological condition of the host to obtain maximum food under restricted nutritional conditions. Approximate digestibility (AD) was higher following parasitization but the efficiency of conversion of digested food (ECD) of the parasitized hosts was lower. This suggests that resources available to the parasitoid larvae are enhanced in the parasitized hosts. We evaluated the physiological changes caused by injection of calyx fluid (polydnavirus) plus venom (C+V) in nonparasitized hosts. Injection of C+V into the nonparasitized hosts duplicated the effects of parasitism, namely it increased the AD and decreased the ECD. Furthermore, C+V injections elevated trehalose concentrations in nonparasitized host 7 to 10 d after injection (2nd stadium of the parasitoid larva). Protein content also increased on days 9 and 10 after C+V injection. These results suggest that the nutrients that parasitoid larvae require for their growth increase in the hemolymph of the host during the 2nd stadium of the parasitoid larva.