Interpopulation variation in the prevalence and intensity of parasitic mite infection in the land snail Arianta arbustorum

Abstract. The parasitic mite Riccardoella limacum sucks blood in the lung of its host, the land snail Arianta arbustorum . The infection of various host populations was examined in Switzerland. In a lowland snail population, prevalence of infection did not vary among seasons. However, intensity of mite infection in dissected individuals of A. arbustorum was high in autumn, but low in winter and spring when ≤100 mite eggs were found attached to the lung epithelium. A novel, non-invasive parasite screening method was used to estimate the number of mites on living host snails. An analysis of repeatability revealed that 92.9% of the snails were correctly classified as infected or non-infected with this non-invasive method. Prevalence of mite infection was examined in 997 adults of A. arbustorum from 11 natural populations distributed over an altitudinal gradient ranging 335–2360 m. No infected snails were found in 7 populations, while in the remaining 4 populations the prevalence of mite infection ranged 45.8–77.8%. Intensity of infection also differed among the 4 host populations. No geographic pattern in prevalence of infection was found. However, parasitic mites did not occur in snail populations situated at elevations of 1290 m or higher. A possible explanation for this finding could be that the host's hibernation period may be too long at high elevations for mites and their eggs to survive. At low elevations, other factors may affect the presence of R. limacum in the lung of A. arbustorum .     

Parasitic mites influence fitness components of their host, the land snail Arianta arbustorum

Abstract. Parasites can influence the population dynamics of their hosts by affecting life-history strategies and behavior. The hematophageous mite Riccardoella limacum lives in the lung cavity of terrestrial gastropods. We used correlational and experimental approaches to investigate the influence of parasite infection on the behavior and life-history traits of the simultaneously hermaphroditic land snail Arianta arbustorum , a common host of R. limacum. Naturally infected individuals of A. arbustorum , collected in the wild, showed a decreased activity compared with uninfected snails. The reproductive output, expressed as the number of eggs deposited in a reproductive season, was reduced in mite-infected hosts. However, the hatching success of the eggs laid by parasitized snails was slightly higher than that of uninfected individuals. We also examined winter survival in 361 adults of A. arbustorum collected from four natural populations. The prevalence of mite infection ranged from 44.8% to 70.1% in three populations (snails in the fourth population were not infected). Winter survival was reduced in infected snails in two out of three populations. Furthermore, experimentally infected snails from an uninfected population showed a reduced winter survival compared with control snails. Our results indicate that parasite pressure imposed by members of R. limacum may influence life history in A. arbustorum.     

Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite (Tetranychus kanzawai) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.     

Behavioural response and winter survival of mated and unmated diapausing females of the Tetranychus atlanticus-urticae complex (Acari, Tetranychidae)

Behavioural responses were studied in mated and unmated females of a Dutch strain of the spider mite Tetranychus urticae which were destined to enter diapause. Observations were confined to the period between acquirement of the winter coloration by the females (a few days after the last moult) and their entering of artificial hibernation sites offered to the mites on the host leaves. Unmated females were found to stay longer on the leaf surface than mated females; they entered the hibernation sites significantly later than mated females. The delay in the search for hibernation sites shown by unmated females may be seen as a behavioural adaptation to enhance the chance of being fertilized before hibernation. Winter survival of mated and unmated diapausing females of the same strain of mites was studied both in the laboratory at a constant temperature of 2±1°C and outdoors under natural climatic conditions in Amsterdam during the winter of 1990–1991. Survival was high under both conditions for mated as well as unmated females; no significant differences in survival were found between both types of female. Observations on post-diapause females of Tetranychus atlanticus (a mite belonging to the T. urticae complex) sampled from strawberry fields near Moscow in spring, showed that at most 10% of the females of this natural spider mite population were unmated. Both mated and unmated females had survived winter temperatures of -28 to -30°C.     

Experimental exposure of Helisoma trivolvis and Biomphalaria glabrata (Gastropoda) to Ribeiroia ondatrae (Trematoda)

Experimental infections provide an important foundation for understanding host responses to parasites. While infections with Ribeiroia ondatrae cause mortality and malformations in a wide range of amphibian second intermediate host species, little is known about how the parasite affects its snail first intermediate hosts or even what species can support infection. In this study, we experimentally exposed Helisoma trivolvis, a commonly reported host of R. ondatrae, and Biomphalaria glabrata, a confamilial snail known to host Ribeiroia marini, to increasing concentrations of embryonated eggs of R. ondatrae obtained from surrogate definitive hosts. Over the course of 8 wk, we examined the effect of parasite exposure on infection status, time-to-cercariae release, host size, and mortality of both snail species. Helisoma trivolvis was a highly competent host for R. ondatrae infection, with over 93% infection in all exposed snails, regardless of egg exposure level. However, no infections were detected among exposed B. glabrata, despite previous accounts of this snail hosting a congener parasite. Among exposed H. trivolvis, high parasite exposure reduced growth, decreased time-to-cercariae release, and caused marginally significant increases in mortality. Interestingly, while B. glabrata snails did not become infected with R. ondatrae, individuals exposed to 650 R. ondatrae eggs grew less rapidly than unexposed snails, suggesting a sub-lethal energetic cost associated with parasite exposure. Our results highlight the importance of using experimental infections to understand the effects of parasite exposure on host- and non-host species, each of which can be affected by exposure.     

Distribution of deformed wing virus within honey bee (Apis mellifera) brood cells infested with the ectoparasitic mite Varroa destructor

The distribution of deformed wing virus (DWV) in adult female Varroa destructor and in their progeny in relation to the pupal host bee was investigated to evaluate acquisition and transfer of DWV by the mites. The results clearly show that adult female mites regularly act as competent vectors of DWV, however, they do not acquire or transfer virus on all possible occasions. Mother mites may contain DWV while the pupal host remains free from overt infection and both mother mites and mite progeny may not acquire detectable amounts of DWV from an infected host bee. However, a majority of mites feeding on pupae that emerge with deformed wings will contain DWV. The data also demonstrates that both adult and immature mite progeny most likely acquire DWV from DWV-infected host bees and not from their mother mites. Possible explanations for the obtained results are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Monitoring northern fowl mites (Acari: Macronyssidae) in caged laying hens: feasibility of an egg-based sampling system

Northern fowl mites were monitored on a caged-layer operation in southern California for 22 mo. Three experienced observers underestimated actual numbers of mites in the vent region approximately 80% of the time. Errors were higher for heavy infestations. Observer estimates were highly correlated with each other (r > 0.89, P < 0.01) and with mite numbers estimated by vent feather removal (r > 0.82, P < 0.01). Mites on hens varied between houses and over time. Molting consistently reduced mite numbers, but did not eliminate then in a flock. Long-term monitoring of individual sentinel hens demonstrated that some hens would support high numbers of mites for several months or more. Use of a new sequential hen sampling plan required approximately 1 min per hen, if mite numbers were estimated. At this site, treatment decisions often could be reached in < 20 min per house. Mite scores (index of estimated mites per hen) were well correlated with percentage of hens infested in both test houses. In a chronically infested house, prevalence of mites on eggs averaged 8.5%, with a range of 0-55%. Applications of tetrachlorvinphos-dichlorvos by the producer appeared to be based on mites on > about 20% of eggs. The chemical was marginal for controlling mites on hens (25% reduction in percentage of hens infested), but effectively reduced mites on eggs (95% fewer mites on eggs at 1 wk and 90% at 2 wk). When data were grouped by mite index score on hens, there was a strong relationship (r2 = 0.83, P < 0.01) between mite prevalence on eggs and the scores of the hens which laid them. Sampling 100 eggs evenly spaced in a house required < 7 min, and adult mites were easily seen. Sampling mites on eggs appears to be useful to localize at least high-level infestations, and egg-based sampling for mites merits further investigation.     

Geographical structuring of feather mite assemblages from the Australian brush-turkey (Aves: Megapodiidae)

Populations of a host species may exhibit different assemblages of parasites and other symbionts. The loss of certain species of symbionts (lineage sorting, or "missing-the-boat") is a mechanism by which geographical variation in symbiont assemblages can arise. We studied feather mites and lice from Australian brush-turkeys (Aves: Megapodiidae: Alectura lathami) and expected to observe geographical structuring in arthropod assemblages for several reasons. First, because the brush-turkey is a sedentary ground-dwelling bird, we predicted that geographically close host populations should share more similar arthropod assemblages than distant ones. Second, because brush-turkeys do not brood their young, vertical transfer of arthropods is unlikely, and brush-turkeys probably acquire their mites and lice at social maturity through contact with other birds. Young birds could disperse and found new populations without carrying complete sets of symbionts. We predicted that young birds would have fewer species of arthropods than older birds; in addition, we expected that males (which are polygynous) would have more species than females. Birds were sampled from 12 sites (=populations) along the east coast of Queensland, Australia, that were separated by a distance of 12.5-2,005 km. In total, 5 species of mites from the Pterolichidae and 1 species from the Ascouracaridae were found. Two species of lice were collected but in numbers too low to be statistically useful. Differentiation of mite assemblages was evident; in particular, Leipobius sp. showed 100% prevalence in 3 host populations and 0% in the remaining 9. A dendrogram of brush-turkey populations based on mite assemblages showed 2 geographically correlated clusters of sites, plus 1 cluster that contained 2 sites near Brisbane and 1 approximately at a distance of 1,000 km. There was no strong effect of host age or sex on number of mite species carried. Horizontal transfer of feather mites by hippoboscid flies, in addition to physical contact between hosts, may play a role in homogenizing symbiont assemblages within populations.     

Belowground microbial symbiont enhances plant susceptibility to a spider mite through change in soybean leaf quality

To examine how rhizobia affect the chemical and nutrient status in leaves of soybean (Glycine max L.), and how rhizobia change plant susceptibility to a generalist spider mite (Tetranycus urticae), we cultivated root-nodulating soybeans (R+) and their non-nodulating mutant (R−) in a common garden. We experimentally fertilized the plants with nitrogen to examine effects of rhizobia on the plant traits and plant susceptibility to spider mites at different nitrogen levels. R+ plants produced more leaves containing greater nitrogen and less total phenolics than R− plants. Spider mites fed on R+ leaves produced more eggs than those fed on R− leaves. The positive effect of rhizobia on spider mite fecundity could be due to an increase in foliar N content and/or to a decrease in concentration of phenolics. Although root nodule mass did not differ among different nitrogen levels, ureide-N, an indicator of nitrogen provided by rhizobia, in xylem sap decreased at moderate and high soil nitrogen levels. Therefore, we expected that rhizobia effects on egg production of the spider mite would decrease in high soil nitrogen conditions. However, the effect of rhizobia was still maintained even at high soil nitrogen levels. Thus, soil nitrogen and rhizobia may independently affect the reproductive performance of the spider mite.     

Odonates,gregarines and water mites: why are the same host species infected by both parasites?

1. Damselflies and dragonflies are widely parasitised insects and numerous studies have tried to understand this host–parasite relationship. However, most of these studies have concentrated on a single host species, neglecting the larger pattern within the Odonata order. 2. The aim of this paper was to examine different damselfly and dragonfly species for common endo‐ and ectoparasites and whether a general infection pattern can be found. Additionally, the goal was to investigate whether the phylogeny of the host species could explain these possible infection patterns. To this end, a dataset from the existing literature was compiled and the prevalence of endoparasitic gregarines and ectoparasitic water mites was analysed for 46 different odonate species. 3. Three distinct patterns were found: (i) most of the odonate host species had both gregarines and water mites, rather than only either one or neither; (ii) there appears to be a positive association between gregarine and water mite prevalences across host species; (iii) a weak phylogenetic signal was detected in gregarine prevalence and a strong one in water mite prevalence. 4. It is hypothesised that, due to the infection and transmission mechanisms by which water mites and gregarines infect different odonate host species, parasitism is aggregated to common, high‐density species. However, much research is needed in order to fully understand this relationship between odonates and their parasites, especially within the same host populations and host species assemblages.     

Development, long-term survival, and the maintenance of fertility in Neoseiulus californicus (Acari: Phytoseiidae) reared on an artificial diet

The effectiveness of non-prey food items, such as pollen, honeydew, and microbes, in maintaining phytoseiid mite populations is widely accepted. However, the availability of such naturally occurring non-prey foods varies with the season and surrounding environment; thus, it is difficult to manipulate and maintain supplies of these food sources. A great deal of research has examined the development and reproduction of phytoseiid mites on artificial diets. Although phytoseiid mites frequently develop, several studies have detected low fecundities of adult females reared on artificial diets. Therefore, the use of artificial diets for commercial propagation is often difficult. However, the potential of artificial diets to maintain phytoseiid mite populations has not yet been evaluated. In this study, we investigated the developmental success and survival of Neoseiulus californicus (McGregor) on an artificial diet. This mite may be one of the most effective phytoseiid species used in agricultural systems for the control of spider mites. N. californicus successfully developed on the artificial diets: 93.5-100% of individuals reached adulthood 4-7 days after hatching. The survival rates of gravid adult females maintained on the AD-1 artificial diet composed of yeast components, saccharides, and egg yolk at 25 degrees C were 100, 80, and 48.9% over 36, 60, and 90 days, respectively. Moreover, >80% of the surviving females maintained on AD-1 for 36 or 60 days laid eggs after being switched to a diet of the spider mite Tetranychus urticae Koch, although they had laid few eggs during the maintenance periods on the artificial diet. Our results indicate that artificial diets can serve as a potentially useful food source for the long-term maintenance of N. californicus populations.     

Sexually transmitted disease in a promiscuous insect, Adalia bipunctata

Abstract.

• 1 Sexually transmitted diseases (STDs) have rarely been reported in insects and other invertebrates. The majority of those reported involve organisms where sexual transmission is augmented by either vertical (i.e. inherited) transmission, or horizontal transmission, independent of host sexual activity.
• 2 We here demonstrate the existence of an STD in the coccinellid beetle Adalia bipunctata. This species bears a parasitic mite of the genus Coccipolipus. We show that, like many other podapolipid mites, this mite is transmitted between host individuals at a high rate during copulation. It also appears to be transmitted at a low rate between non-copulating individuals.
• 3 We show that infected female A.bipunctata produced eggs at a reduced rate, and that the eggs produced by infected females have highly decreased viability. However, no effect of infection upon host longevity was observed.
• 4 The results are discussed in relation to the incidences of sexually transmitted disease in invertebrates in general, the causes of disease symptoms, and the importance of this disease in the evolution of A.bipunctata.

     

Supercooling ability in two populations of the land snail Helix pomatia (Gastropoda: Helicidae) and ice-nucleating activity of gut bacteria

The land snail Helix pomatia (Gastropoda: Helicidae) is widely distributed in Northern and Central Europe where it may experience subzero temperatures during winter months. Its supercooling ability was studied in two populations of H. pomatia. One population originated from Southern Sweden (Gotaland) and the other from Central France (Auvergne). In the experimental design, they were acclimated, over 2 weeks, to artificial winter conditions (hibernation, T=5 degrees C). The Swedish snails showed a rather limited supercooling ability (temperature of crystallization, T(c)=-6.4+/-0.8 degrees C), significantly greater, however, than the supercooling capacity of the population from France (T(c)=-4.6+/-1.4 degrees C). In artificial spring conditions (3 months of hibernation followed by a progressive acclimation, over 2 weeks, to activity at T=20 degrees C), both populations exhibited a similar high T(c) (-2.0+/-1.0 degrees C). The lower T(c) of hibernating Swedish snails could be due to a greater loss of body water, accompanied by a higher concentration of solutes in the hemolymph. In both populations, the variation in hemolymph osmolality measured between hibernating (250-270 mOsm kg(-1)) and active (165-215 mOsm kg(-1)) snails may be explained by the variation in body water mass and did not suggest the production of colligative cryoprotectants. Moreover, the three bacterial strains, Buttiauxella sp., Kluyvera sp., and Tatumella sp. (Enterobacteriaceae) which were isolated from fed snails, but absent in starved snails, did not show any ice-nucleating activity at temperatures higher than -9 degrees C. Only the strain Kluyvera sp. initiated nucleation at -9 degrees C. This strain, therefore, is a weak, also termed a Type III or Class C ice-nucleating active bacterium, but with no influence on the supercooling ability of individual snails. In summary, fluctuations in body water mass of hibernating snail populations, triggering changes in osmolyte concentration, rather than the presence of endogenous ice-nucleating-active bacteria, accounts for fluctuations in their T(c).     

Host-plant species modifies the diet of an omnivore feeding on three trophic levels

The diet choice of omnivores feeding on two adjacent trophic levels (either plants and herbivores or herbivores and predators) has been studied extensively. However, omnivores usually feed on more than two trophic levels, and this diet choice and its consequences for population dynamics have hardly been studied. We report how host-plant quality affects the diet choice of western flower thrips feeding on three trophic levels: plants (cucumber or sweet pepper), eggs of spider mites and eggs of a predatory mite that attacks spider mites. Spider mites feed on the same host plants as thrips and produce a web that hampers predator mobility. To assess the indirect effects of spider mites on predation by thrips, the thrips were offered spider-mite eggs and predatory-mite eggs on cucumber or sweet pepper leaf discs that were either clean, damaged by spider mites but without spider-mite web, or damaged and webbed. We show that, overall, thrips consumed more eggs on sweet pepper, a plant of low quality, than on cucumber, a high quality host plant. On damaged and webbed leaf discs (mimicking the natural situation), thrips killed more predator eggs than spider-mite eggs on sweet pepper, but they killed equal numbers of eggs of each species on cucumber. This is because web hampered predation on spider-mite eggs by thrips on sweet pepper, but not on cucumber, whereas it did not affect predation on predatory-mite eggs. We used the data obtained to parameterize a model of the local dynamics of this system. The model predicts that total predation by the omnivore has little effects on population dynamics, whereas differential attack of predator eggs and spider-mite eggs by the omnivore has large effects on the dynamics of both mite species on the two host plants.     

The role of host phenology in determining the incidence of an insect sexually transmitted infection

Changes in the timing of life history events within the year alter the degree to which the activity patterns of different species coincide, making the dynamics of interspecific interactions sensitive to the phenology of the interacting parties. For parasites, the availability of suitable hosts to infect represents a crucial determinant of dynamics, and changes in the host (and parasite) phenology may thus alter disease epidemiology and the conditions for disease maintenance. We tested the hypothesis that the incidence of a sexually transmitted mite infection, Coccipolipus hippodamiae, in Adalia bipunctata ladybird beetles in Sweden was determined by host phenology, namely presence/absence of sexual contact between cohorts of the host. We observed that the pattern of mite presence/absence across Swedish A. bipunctata populations was highly reproducible between years, implying a persistent biological/ecological basis underlying the incidence. Further, ladybirds from populations where the mite was absent were able to acquire mites during copulation, develop a mite infection, and transmit infection onward, indicating an ecological (rather than biological) driver of mite incidence. Observations of ladybird phenology in natural populations provided evidence of sexual contact between overwintered and new cohort adults in populations where the mite was present. In contrast, new cohort ladybirds in the two northern Swedish populations where the mite was not present had not had sexual contact with the overwintered generation, creating a ‘hard stop’ to mite transmission. We conclude that variation in host phenology may be an important driver of the incidence of sexually transmitted infections (STIs) by determining the presence/absence of sexual contact between generations. More generally, we hypothesize that sensitivity to variation in host phenology will be highest for parasites like STIs that infect one host species, one host life stage and are directly transmitted on contact between host individuals.     

Diseases of Mites

An overview is given of studies on diseases of mites. Knowledge of diseases of mites is still fragmentary but in recent years more attention has been paid to acaropathogens, often because of the economic importance of many mite species. Most research on mite pathogens concerns studies on fungal pathogens of eriophyoids and spider mites especially. These fungi often play an important role in the regulation of natural mite populations and are sometimes able to decimate populations of phytophagous mites. Studies are being conducted to develop some of these fungi as commercial acaricides.Virus diseases are known in only a few mites, namely, the citrus red mite and the European red mite. In both cases, non-occluded viruses play an important role in the regulation of mite populations in citrus and peach orchards, respectively, but application of these viruses as biological control agents does not seem feasible. A putative iridovirus has been observed in association with Varroa mites in moribund honeybee colonies. The virus is probably also pathogenic for honeybees and may be transmitted to them through this parasitic mite.Few bacteria have been reported as pathogens of the Acari but in recent years research has been concentrated on intracellular organisms such as Wolbachia that may cause distorted sex ratios in offspring and incompatibility between populations. The role of these organisms in natural populations of spider mites is in particular discussed. The effect of Bacillus thuringiensis on mites is also treated in this review, although its mode of action in arthropods is mainly due to the presence of toxins and it is, therefore, not considered to be a pathogen in the true sense of the word.Microsporidia have been observed in several mite species especially in oribatid mites, although other groups of mites may also be affected. In recent years, Microsporidia infections in Phytoseiidae have received considerable attention, as they are often found in mass rearings of beneficial arthropods. They affect the efficacy of these predators as biological control agent of insect and mite pests. Microsporidia do not seem to have potential for biological control of mites.     

Chemical investigation of aggregation behaviour in the two-spotted spider mite Tetranychus urticae

The silk produced by the group-living mite Tetranychus urticae provides group protection and is used as an informative material during habitat settlement, egg laying, mating, and dispersal events. In this context, cues contained in the silk and other materials produced by mites [eggs, black faeces (BF) and white faeces + silk (WFS)] were investigated. Chemical compounds were extracted by hexane or methanol, and choice tests were used to determine the individual attractiveness of each extract. For both solvents, individuals did not respond to the extract from eggs and WFS. BF extracts were attractive for both solvents. After separating the BF methanol extract into four different chemical components using thin layer chromatography, no component was determined to be responsible for mite attraction. This work supports the evidence that the faeces of T. urticae do contain substances that promote behavioural changes. Not particular chemical compounds but combinations of them seem to induce the mites’ preference. Moreover, the response of mites to chemicals seemed to be context dependent as mites belonging to populations with different densities differed in their attraction to BF extracts.     

Infestation and Related Ecology of Chigger Mites on the Asian House Rat (Rattus tanezumi) in Yunnan Province,Southwest China

This paper is to illustrate the infestation and related ecological characteristics of chigger mites on the Asian house rat (Rattus tanezumi). A total of 17,221 chigger mites were collected from 2,761 R. tanezumi rats, and then identified as 131 species and 19 genera in 2 families. Leptotrombidium deliense, the most powerful vector of scrub typhus in China, was the first major dominant species on R. tanezumi. All the dominant mite species were of an aggregated distribution among different individuals of R. tanezumi. The species composition and infestations of chiggers on R. tanezumi varied along different geographical regions, habitats and altitudes. The species-abundance distribution of the chigger mite community was successfully fitted and the theoretical curve equation was Ŝ (R)=37e^−(0.28R)². The total chigger species on R. tanezumi were estimated to be 199 species or 234 species, and this further suggested that R. tanezumi has a great potential to harbor abundant species of chigger mites. The results of the species-plot relationship indicated that the chigger mite community on R. tanezumi in Yunnan was an uneven community with very high heterogeneity. Wide geographical regions with large host samples are recommended in the investigations of chigger mites.     

Plagiorchis elegans (Digenea: Plagiorchiidae) infections in Stagnicola elodes (Pulmonata: Lymnaeidae): host susceptibility, growth, reproduction, mortality, and cercarial production.

Eggs of Plagiorchis elegans were readily ingested by Stagnicola elodes of all ages, but were more infective to immature than mature snails. Infection enhanced the growth of the host in a dose-dependent manner. The number of cercariae released by immature snails increased with the age of the snail host; mature snails yielded fewer cercariae. Heavily infected snails tended to die prematurely, thereby reducing their total production of cercariae to levels below those of more lightly infected individuals. Even light infections castrated the snail host. Snails that acquired the infection as juveniles never produced eggs. Actively reproducing snails ceased egg laying within days of infection and never recovered. All parasite effects on the growth and reproduction of the snail host first manifested themselves during the early stages of infection, long before the development of daughter sporocysts and cercariae, and are therefore attributable to the effects of mother sporocysts. The study provides insight into how this natural enemy of mosquito larvae may be established in natural snail populations by means of strategically timed introductions of parasite eggs, with a goal of maximizing cercarial production for the biological control of sympatric mosquito larvae.     

Effectiveness of vacuum cleaning and wet cleaning in reducing house-dust mites,fungi and mite allergen in a cotton carpet: A case study

In order to evaluate the effect of continuous, thorough vacuuming on house dust organisms and mite allergen, a cotton carpet was vacuumed every other day, six times in total. Seven weeks later, the carpet was cleaned by means of spray extraction. Samples were taken before and after this wet cleaning.In total 1150 g of dust was collected, containing approximately 174 000 arthropods (dead and alive) and 9000×10⁶ fungal spores. In the course of the experiment, the amount of dust collected at each vacuuming decreased. The number of extracted house dust mites did not decrease significantly, but that of the predator miteCheyletus did. The number of extracted fungal spores showed a significant decrease (from 142 to 16×10⁶ spores/m² per minute vacuuming), as did the extracted mite allergen per m². After 7 weeks the number of mite eggs and complete house dust mites had increased enormously. After cleaning by spray extraction another increase in the number of complete mites and mite eggs was found, while the amount of mite allergen was diminished.The population growth of the house dust mite between the 6th and the 7th vacuuming is probably due to the decrease of their most important predator,Cheyletus. After the wet cleaning a number of extra eggs hatched, probably due to the high humidity in the carpet. The procedures used in this study to combat house dust mites may have an adverse effect in the long run.