Contamination of Passenger Trains with Dermatophagoides (Acari: Pyroglyphidae) Mite Antigen in Japan

Passenger trains were surveyed for contamination with Dermatophagoides farinae Hughes and Dermatophagoides pteronyssinus (Trouesart) mites in Japan. A total of 492 dust samples were collected from upholstered seats in six commuter trains, one long-distance express train and three night trains in October, 1996 and January, April, and July, 1997. Mite antigen levels contained in fine dust fractions of these samples were measured by an enzyme- linked immunosorbent assay. Most samples obtained from commuter trains showed relatively high mite antigen levels of >10gm^–2 (corresponding to >100 mites). Express and night trains showed lower antigen levels per square meter, but higher mite antigen levels per gram of fine dust than commuter trains, indicating relatively high mite antigen densities. Seasonal comparisons indicated that commuter trains showed the highest mean antigen level per square meter in winter (January), whereas the highest antigen level per gram of fine dust was observed in summer (July) in express and night trains.     

Interference in foraging behaviour of European and American house dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae (Acari: Pyroglyphidae) by catmint, Nepeta cataria (Lamiaceae)

The European and American house dust mites, Dermatophagoides pteronyssinus and D. farinae, have a huge impact upon human health worldwide due to being the most important indoor trigger of atopic diseases such as asthma, rhinitis and atopic dermatitis. Preceding studies have shown that the behavioural response of house dust mites towards volatile chemicals from food sources can be assessed using a Y-tube olfactometer assay. In the current study, we used this assay to investigate, for the first time, the ability of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), known to repel other ectoparasites affecting human and animal health, to interfere with the attraction of D. pteronyssinus and D. farinae towards a standard food source (fish flakes). Two distinct chemotypes (A and B), enriched in the iridoid compounds (4aS,7S,7aR)-nepetalactone and (4aS,7S,7aS)-nepetalactone, and the sesquiterpene (E)-(1R,9S)-caryophyllene, were used. Initial assays with a hexane extract of fish flakes (FF extract) confirmed attraction of mites to this positive control (P < 0.001 and P < 0.05 for D. pteronyssinus and D. farinae respectively), but when presented in combination with either N. cataria chemotype, tested across a range of doses (10, 1, 0.1 and 0.01 μg), decreasing attraction of mites to their food source was observed as the dose augmented. Our study shows that N. cataria, enriched in iridoid nepetalactones and (E)-(1R,9S)-caryophyllene, exhibits potent repellent activity for house dust mites, and has the potential for deployment in control programmes based on interference with normal house dust mite behaviour.     

A simple model for predicting the effect of hygrothermal conditions on populations of house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae)

A simple mite population index (MPI) model is presented which predicts the effect on house dust mite populations of any combination of temperature and relative humidity (RH). For each combination, the output is an index, or multiplication factor, such that 1.1 indicates 10% population growth and 0.9 indicates 10% population decline. To provide data for the model, laboratory experiments have been carried out using lab cultures of Dermatophagoides pteronyssinus. The population change was observed for mites held in steady-state conditions at different combinations of temperature and RH over 21 days. From the results, a best-fit equation has been derived which forms the basis of the MPI model. The results also enable a new term to be defined: the Population Equilibrium Humidity, PEH, the RH for a given temperature at which house dust mite populations neither grow nor decline. It is similar to Critical Equilibrium Humidity, the RH below which house dust mites are unable to maintain water balance, but relates to a population of mites (rather than a physiological phenomenon) and is more able to take account of the observed effects of extremes of temperature and RH. Compared with previous population models, the MPI model is potentially more accurate and comprehensive. It can be combined with other simple models (described in previous papers), such as BED, which simulates the average hygrothermal conditions in a bed, given room␣conditions, and Condensation Targeter II, which simulates room conditions given a range of easily obtainable inputs for climate, house type and occupant characteristics. In this way it is now possible, for any individual dwelling, to assess the most effective means of controlling mite populations by environmental means, such as by improving standards of ventilation and insulation, or by modifying the occupant behaviour that affects the hygrothermal environment within a dwelling. Although the MPI model requires further development and validation, it has already proved useful for understanding more clearly how the different hygrothermal conditions found in beds and bedrooms can affect mite populations. It has also demonstrated that there is considerable scope for controlling mites by environmental means in cold winter climates such as the UK.     

The colonisation of new houses by house dust mites (Acari: Pyroglyphidae)

House dust mites,Dermatophagoides species (Acari: Pyroglyphidae), produce allergens, known for the provocation of asthma and other allergic reactions. To determine the time needed for complete colonisation of a new house by house dust mites, dust samples were collected from carpets of houses varying from 2 weeks to 2 years in age. In contrast to the expectation, no relation was found between age of the houses on the one hand and average levels of mite-allergensDer pI andDer pII and mite numbers on the other. However, presence of dogs appeared to be positively related to allergen levels. Furthermore, carpets in bedrooms appeared to contain more allergens than carpets in living-rooms. Finally, the age of the mattress was not related to allergen levels of bedroom floors.     

On the abundance ofDermatophagoides pteronyssinus (Trouessart, 1897) (Pyroglyphidae: Acarina) in house dust

The dominance of the Pyroglyphidae in house dust has been influenced by a number of factors. The humidity in houses dropped recently to such an extent that only Pyroglyphidae can survive. When temperature and relative humidity are favorable for Acarus siro and Glycyphagus destructor as well as Dermatophagoides pteronyssinus, Dermatophagoides diminished in numbers by competition. Introduction of the predator Cheyletus eruditus into this mixed breeds causes the extermination of Dermatophagoides. The vacuum cleaner trapped mites, but Dermatophagoides was protected by its habit to hide in cracks and crevices. The use of insecticides has a more killing effect on Acarus and Glycyphagus than on Dermatophagoides.     

Acaricidal effects of herb essential oils against Dermatophagoides farinae and D. pteronyssinus (Acari: Pyroglyphidae) and qualitative analysis of a herb Mentha pulegium(pennyroyal)

This experiment was undertaken to screen the acaricidal effects of herb essential oils (pennyroyal, ylang ylang, citronella, lemon grass, tea tree, and rosemary) at different doses (0.1, 0.05, 0.025, 0.0125, and 0.00625 microliter/cm(2)) and exposure times (5, 10, 20, 20, 30 and 60 min) on house dust mites Dermatophgoides farinae and D. pteronyssinus. The most effective acaricidal components of pennyroyal (Mentha pulegium) were analyzed using a gas chromatography-mass spectrometer (GC-MS). Of these essential oils, the most effective was pennyroyal, which is composed essentially of pulegone (> 99%), at a dose of 0.025 microliter/cm(2), which at an exposure time of 5 min killed more than 98% of house dust mites. In the pennyroyal fumigation test, the closed method was more effective than the open method and maximum acaricidal effect was 100% at 0.025 microliter/cm(2), 60 min. The results show that herb essential oils, in particular, pennyroyal was proved to have potent acaricidal activity.     

Predicting the population dynamics of the house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) in response to a constant hygrothermal environment using a model of the mite life cycle

A generalised model of the life cycle of a house dust mite, which can be tailored to any particular species of domestic mite, is presented. The model takes into account the effects of hygrothermal conditions on each life cycle phase. It is used in a computer simulation program, called POPMITE, which, by incorporating a population age structure, is able to predict population dynamics. The POPMITE simulation is adapted to the Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) (DP) mite using published data on the egg development period, total development period, adult longevity, mortality during egg development, mortality during juvenile development, and fecundity of individual DP mites held at a range of constant hygrothermal conditions. An example is given which illustrates how the model functions under constant hygrothermal conditions. A preliminary validation of POPMITE is made by a comparison of the POPMITE predictions with published measurements of population growth of DP mites held at a range constant hygrothermal conditions for 21 days. The POPMITE simulation is used to provide predictions of population growth or decline for a wide range of constant relative humidity and temperature combinations for 30 and 60 days. The adaptation of the model to correctly take account of fluctuating hygrothermal conditions is discussed.     

A comparison of the water balance characteristics of Typhlodromus occidentalis and Amblyseius finlandicus mites (Acari: Phytoseiidae) and evidence for the site of water vapour uptake

To determine how adult Typhlodromus occidentalis, a mite used in the biological control of spider mites, thrive in arid western North America, the water balance characteristics of adult females were compared to those of a laboratory colony of Amblyseius finlandicus originating from Finnish apple orchards. The mites contained comparable amounts of water (73.6 and 74.9%, respectively, for T. occidentalis and A. finlandicus), absorbed water from the air between 86% and 92% relative humidity (RH) (critical equilibrium humidity) and drank free water from droplets. Typhlodromus occidentalis were distinguished, however, by having lower net water loss rates (0.8% versus 1.3% h–1 at 0% RH, 20°C for A. finlandicus), a feature that enables them to retain water more effectively. Above the critical equilibrium humidity water was lost by adult female T. occidentalis whose mouth parts had been blocked with wax, implying an oral uptake mechanism for the absorption of water vapour. © Rapid Science Ltd. 1998     

Fumigant toxicity of cassia bark and cassia and cinnamon oil compounds to <Emphasis Type="Italic">Dermatophagoides </Emphasis><Emphasis Type="Italic">farinae </Emphasis>and <Emphasis Type="Italic">Dermatophagoides pteronyssinus</Emphasis> (Acari: Pyroglyphidae)

The toxicity to adults of the American house dust mite, Dermatophagoides farinae, and the European house dust mite, Dermatophagoides pteronyssinus, of cassia bark and cassia and cinnamon oil compounds was examined using residual contact and vapour-phase toxicity bioassays. Results were compared with those of the currently used acaricides: benzyl benzoate and dibutyl phthalate. The acaricidal principles of cassia bark were identified as (E)-cinnamaldehyde and salicylaldehyde. In fabric-circle residual contact bioassays with adult D. farinae, salicylaldehyde (17.3 mg/m²) and (E)-cinnamaldehyde (25.8 mg/m²) were 2.5 and 1.7 times more toxic than benzyl benzoate (43.7 mg/m²), respectively, based on 24-h LD₅₀ values. The acaricidal activity was more pronounced in benzaldehyde, menthol, α-terpineol, and thymol (70.8–234.3 mg/m²) than in dibutyl phthalate (281.0 mg/m²). Against adult D. pteronyssinus, salicylaldehyde (17.3 mg/m²) and (E)-cinnamaldehyde (19.3 mg/m²) were 2.4- and 2.2-fold more active than benzyl benzoate (41.9 mg/m²). The toxicity of benzaldehyde, menthol, α-terpineol, and thymol (75.3–179.2 mg/m²) was higher than that of dibutyl phthalate (285.1 mg/m²). In vapour-phase toxicity tests with adult D. farinae, the test compounds described were much more effective in closed—but not in open—containers, indicating that the effect of these compounds was largely a result of action in the vapour phase.     

Review Geographic differences in host specialization between the symbiotic water mites Unionicola formosa and Unionicola foili (Acari: Unionicolidae)

The host specificity and population genetic structure of the symbiotic water mites Unionicola foili from the host mussel Utterbackia imbecillis and Unionicola formosa from the mussels Pyganodon cataracta, Pyganodon grandis and Anodonta suborbiculata were examined over a broad geographical scale in order to determine the extent to which specialization by these water mites is structured geographically. The behavioural responses of U. foili and U. formosa were highly host-species specific, with adults of both species exhibiting negative phototaxis in the presence of a chemical factor from the species of mussel with which the mites had been associated in the field. The photobehaviour of these water mites in the presence of water from a non-host mussel varied depending on the species in question. Although U. foili from U. imbecillis exhibited negative phototaxis in water modified by A. suborbiculata, mites from this latter host did not exhibit a directional response in U. imbecillis water. Unionicola foili and U. formosa from A. suborbiculata were positively phototactic when they were exposed to water modified by either species of Pyganodon. The photoresponse of U. formosa from P. cataracta and P. grandis was positive in the presence of water modified by U. imbecillis and A. suborbiculta. However, these mussel-mites showed no directional response in water modified by their alternate species of Pyganodon. Unionicola foili and the host-associated populations of U. formosa were examined for allozyme variation at eight loci to determine the pattern and degree of genetic variation. There was a high degree of genetic differentiation when mite populations from the two species of Pyganodon were compared with U. foili or U. formosa from A. suborbiculata. These populational groupings were fixed for different alleles at two enzyme loci. The results of this study indicate that populations of U. formosa from P. cataracta and P. grandis are reproductively isolated from U. foili from U. imbecillis and from U. formosa from A. suborbiculata and contend that host specificity is an important mechanism in restricting gene flow among these populational groupings. Furthermore, this study indicates that specialization among unionicolid water mites can vary geographically, owing to differences in geographic distribution of available hosts and differences in host use.Exp Appl Acarol 22: 683697 © 1998 Kluwer Academic Publishers     

Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75-85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93-97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.     

Studies on the critical water mass and the rehydration potential of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae)

In unfed adult Dermacentor marginatus and D. reticulatusticks survival and capability to restore water balance after loss of high percentages of exchangeable body water were investigated. Furthermore, it was examined how frequently dehydrated ticks of these species were able to rehydrate by uptake of atmospheric water vapour. The critical water mass, defined as the water mass remaining in a tick at the nonambulatory state, differed between light and heavy weight groups and averaged 62.4 and 55.8%, respectively, of the total body water of fully hydrated ticks in females, and 54.4 and 51.1% respectively, in males of D. marginatus. In D. reticulatus, the corresponding figures were 55.9 and 54.7% in females and 52.1 and 52.7% in males. All ticks survived dehydration to 50, 75 or 100% of the critical water mass, and 96.7% of the D. marginatus ticks and 95.8% of the D. reticulatus ticks compensated water losses during subsequent incubation at 95% relative humidity (r.h.) and 20°C. Unfed females and males of both Dermacentor spp. were capable to balance water loss very frequently over a period of several months. When ticks were repeatedly dehydrated at 0% r.h. for 7 days and rehydrated at 95% r.h. and 20°C, females and males of D. marginatus reached the 50% mortality after 22 and 29 cycles of de- and rehydration, respectively, during 211 and 285 days, respectively. In D. reticulatus, 50% of females and males survived 23 and 17 cycles, respectively, during 248 and 186 days, respectively. Rehydration weights were as high or even higher as those of ticks kept at permanent 95% r.h.     

Studies on survival and water balance of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae)

The water content, the survival time at various relative humidities(r.h.) and the critical equilibrium activity of unfed adultDermacentor marginatus and D.reticulatus ticks were investigated at a constant temperature of20 °C. It was also examined whether these ticks use liquidwaterto compensate water loss. Both Dermacentor spp. showed nosignificant differences in water content in relation to body mass. The meanwater content of D. marginatus and D.reticulatus was 54.6% and 54.7%, respectively, in females and 56.3%and 57.0%, respectively, in males. The survival time of unfed adults prolongedwith decreasing saturation deficits. On average, males survived longer thanfemales and D. marginatus ticks survived mostly longerthanD. reticulatus ticks. The 50% mortality period rangedbetween 40 d at 33% r.h. and 420 d at 95% r.h. in D.marginatus, and between 43 d at 33 r.h. and 366 d at 95% r.h. inD. reticulatus. The critical equilibrium activity of unfedadults was estimated to be 0.84 for both species and was independent of sex.When dehydrated adult D. marginatus and D.reticulatus ticks were offered liquid water, only a few slightlygained weight while most further lost weight. Liquid water was not attractivefor dehydrated or non-dehydrated ticks and drinking was not observed. Aftersubmerging in water for 2 d, most of the dehydrated ticks had gained weight.