Acarus Farris Research Articles

Hay diseases in Iceland

Diseases due to work in hay dust have long been known in Iceland and the first written records of them appear in the beginning of the 17th century. At the end of the 18th century, a district doctor alleges that they cause many deaths in the country. In the latter part of the 20th century, research was started to investigate the causes and nature of hay diseases in Iceland. Studies of allergens showed high levels of storage mites in hay. Highest levels were of Tarsonemus sp., Acarus farris and Lepidoglyphus destructor. A several micro-fungi were also found, most commonly Rhizopus sp., Penicillium sp. and Aspergillus sp. Micropolyspora faeni was also found in all hay samples. A study was done on people aged 6-50 years in two districts in Iceland. In one district farmers used almost exclusively dry hay and in the other they used 80-90% silage. There was no difference in IgE-mediated allergy between the provinces, but most had positive skin tests for L. destructor and cattle. Those with symptoms connected with hay dust most often reported nasal symptoms (79%), eye symptoms (63%), cough (41%), dyspnea (32%) and fever (21%). Those who had positive skin reaction complained most often of nose and eye symptoms. A study was also conducted on subjects aged 16-87 years from the same regions investigating precipitin tests for M. faeni, Thermoactinomyces vulgaris and Aspergillus fumigatus. Pulmonary symptoms and lung function were also investigated. Precipitin tests were almost exclusively positive for M. faeni, and 5 individuals were positive for A. fumigatus and none for T. vulgaris. The precipitin tests were significantly more often positive in those working almost exclusively with dry hay (72.9% vs. 23.9%). They had also more commonly obstructive pulmonary disease (FEV1/FVC%<70: 24.8% vs. 9.5%) as well as dyspnea when walking on level ground. There was a positive correlation between positive precipitin tests for M. faeni and dyspnea walking on level ground. The sensitivity and specificity of positive precipitin tests for M. faeni were investigated to detect farmer’s lung. The sensitivity was 82% and specificity was only 49%. A survey of emphysema in patients in the only Pulmonary Clinic in the country showed that farmers had more often emphysema than the rest of the country population, and 58% of farmers with emphysema had smoked compared to 94% of other emphysema patients.

The mite Acarus farris inducing defensive behaviors and reducing fitness of termite Coptotermes formosanus: implications for phoresy as a precursor to parasitism

BackgroundThe ecology and evolution of phoretic mites and termites have not been well studied. In particular, it is unknown whether the specific relationship between mites and termites is commensal or parasitic. High phoretic mite densities have often been found to occur in weak termite colonies, suggesting that the relationship is closer to that of parasitism than commensalism.ResultsTo examine this, Coptotermes formosanus was used as a carrier, and Acarus farris as the phoretic mite. We used video recordings to observe termite social immunity behaviors and bioassay to examine termite fitness. Our results showed that the attachment of the mite on the termite can enhance termite social immunity behaviors like alarm vibration and grooming frequency while decreasing the duration of individual grooming episodes in phoretic mites. Further, A. farris phoresy led to a 22.91% reduction in termite abdomen volume and a 3.31-fold increase in termite mortality.ConclusionsWhen termites groom more frequently, the consequence is short duration of grooming bouts. This may be indicative of a trade-off which provides suggestive evidence that frequent social behaviors may cost termites energy. And this caused phoretic behavior hastened termites’ death, and helped propagate the population of mites feeding on dead termites. So, it provides a case for phoresy being a precursor to parasitism, and the specific relationship between A. farris and C. formosanus is closer to parasitism than to commensalism.

Acarus farris hypopus found in stored wheat

To observe the morphological characteristics of Acarus farris hypopus. The breeding mites from stored wheat samples were separated by a shake sieve and direct microscope. The isolations were used for slide preparation, and then the slide was observed under a light microscope for mite identification. The A. farris hypopus was found in the collected wheat samples. Under the microscope the boundary between the propodosoma and hysterosoma of the hypopus was obvious. The bristles on the hysterosoma were short, and the abdomen had a sucker plate. There is A. farris hypopus breeding in the storage wheat, and its morphological characteristics is similar with the characteristics of A. siro hypopus.

Mite species identification in the production of allergenic extracts for clinical use and in environmental samples by ribosomal DNA amplification

The identification of allergy-causing mites is conventionally based on morphological characters. However, molecular taxonomy using ribosomal DNA (rDNA) may be particularly useful in the analysis of mite cultures and purified mite fractions in the production of allergenic extracts. Full-length internal transcribed spacers (ITS1 and ITS2) were obtained from Dermatophagoides farinae, Dermatophagoides pteronyssinus, Dermatophagoides microceras and Euroglyphus maynei (Astigmata: Pyroglyphidae), Glycyphagus domesticus and Lepidoglyphus destructor (Astigmata: Glycyphagidae), Tyrophagus fanetzhangorum, Tyrophagus putrescentiae, Tyrophagus longior, Tyrophagus neiswanderi, Acarus farris and Acarus siro (Astigmata: Acaridae), and Blomia tropicalis (Astigmata: Echymopodidae), using mite-specific primers. Polymerase chain reaction (PCR) products were digested with HpaII and RsaI restriction enzymes in order to produce species-specific PCR restricted fragment length polymorphism (RFLP) profiles. A semi-nested re-amplification step was introduced before the RFLP in order to apply the method to environmental samples. Results demonstrate that rDNA sequences can be used for the unambiguous identification of mite species. The PCR-RFLP system allows the identification of species in purified mite fractions when the availability of intact adult mite bodies for morphological identification is limited. This reliable and straightforward PCR-RFLP system and the rDNA sequences obtained can be of use in the identification of allergy-causing mite species.

Phoresy of astigmatic mites on ticks and fleas in Poland

Abstract Phoresy is an association in which a small animal clings to a larger one exclusively for transportation. We searched for phoretic mites on fleas and ticks of small mammals. A total of 169 fleas of 7 species were collected in the Białowieża Forest (E Poland) and in Kosewo G órne (NE Poland) in July and August in 2007 and 2008. Moreover, 20 nymphs and 12 females of Ixodes hexagonus (Leach, 1815) were collected in the beaver farm of the Research Station of Polish Academy of Sciences in Popielno (NE Poland) in April and May 2009. Phoretic mites were found on 26 fleas (15.4%) of the following species: Megabothris walkeri (Rothschild, 1902), Megabothris turbidus (Rothschild, 1909), Ctenophthalmus agyrtes (Heller, 1896), and Hystrichopsylla orientalis (Smit, 1956). The mites were located mainly on abdominal sternites. Among ticks, only one female was positive for mites, whose larvae (hypopi) were found on its legs. A total of 6 species of mites were identified. On I. hexagonus, we found Acarus farris (Oudemans, 1905) (53 larvae), Acarus siro (L., 1758) (2 larvae), Acarus nidicolous (Griffiths, 1970) (1 larva), Caloglyphus rhizoglyphoides (Zachvatkin, 1937) (1 larva), and Histiostoma feroniarum (Dufour, 1904) (28 larvae), whereas on fleas, 79 larvae of Acarus nidicolous, 1 male of Tyrophagus putrescentiae (Schrank, 1781), and 1 unidentified trombiculid larva. The last 2 mite specimens were found on M. turbidus. This is the first report on phoretic association of the flea H. orientalis and the tick I. hexagonus with mites

Distribution of House Dust Mites in Haskoy Town, Mus

This study was carried out to determine the distribution of house dust mites and the role of the mites on allergic diseases in Haskoy town, Muş. In the study, dust samples were collected from 50 houses in May and July months of 2002 year. Twenty eight (56%) of 50 mites samples examined in May and 20 (40%) of 50 mites samples examined in July were found positive. Dermatophagoides pteronyssinus was found to be the predominant species with 36.34% in May and 34.21%in July. Lepidoglyphus destructor, Cheyletus spp, Acarus spp, Acarus farris, Acotyledon tjidobas, Blomia tjidobas, Rhizoglyphus robini and Chartoglyphus arcuatus had 18.18%, 6.81%, 4.54%, 4.54%, 4.54%, 2.27%, 2.27% and 2.27% percentages in May respectively. On the other hand, L. destructor, Cheyletus spp, Acarus spp, Acarus farris, Allocalvolia habrocytes, A. tjidobas and R. robini had 18.42%, 10.52%, 7.89%, 2.63%, 5.26%, 5.26% and 5.26% in July respectively. Positivity rates of the mites collected from houses of people with allergic disorders was 55.5% while this rate was 56.25% for houses of those without allergic disorders. No statistical relationship was found between encounter with the mites and the patients with allergy. In addition, the number of adobes detected dust mites was higher than the other types of houses.

Mites (Acari) found in flour mills in the Karaj region of Iran

Between March 2004 and July 2005, the mites associated with whole wheat, flour and sweepings (residue from, for example, the floor, equipment and the outside of sacks) in 16 flour mills in the Karaj region of the Tehran Province of Iran were surveyed. Sampling was carried out in the spring (March, April and May), summer (June, July and August) and early autumn (September and October). Mites were found in five of the mills. Nine species were recorded, namely, Acarus farris Oudemans, A. siro Linnaeus, Tyrophagus longior (Gervais), T. putrescentiae (Schrank), Lepidoglyphus destructor (Schrank), Androlaelaps casalis (Berlese), Rhysotritia ardua (C. L. Koch), Acaropsellina sollers (Kuzin) and Cheyletus carnifex Zachvatkin. Mites were found in 94% of the sweeping samples, 68.57% of the flour samples and 53.3% of the whole wheat samples.

Chemical and physical methods for the control of the mite Acarus farris on Cabrales cheese

The astigmatid mite Acarus farris is the main species of mite infesting Cabrales cheese, a traditional Spanish product. This species may reach population density levels of 260 mobile mites/cm 2, resulting in high economic losses. Different chemical and physical methods that were able to control this pest without affecting the organoleptic quality of Cabrales cheese were tested. The efficacy of four short-chain fatty acids (caproic, caprylic, pelargonic and capric) and two sugar alcohols (ribitol and xylitol) were tested under laboratory conditions against mobile stages of A. farris. Only pelargonic acid significantly increased mortality in comparison with controls (63.4 vs. 26.1%, respectively). Additionally, the contact effect of the monoterpene eucalyptol was assessed in cheese maturing rooms at doses of 2.5 and 1.25 μl/cm 2. The first dose effectively controlled A. farris, but its application negatively affected the organoleptic values of the treated cheeses. Finally, the application of the waxy food coating READOM CBR to Cabrales cheeses in maturing rooms, kept the mite population low but negatively modified the external appearance of the cheese, an important quality parameter. The physical approach was based on lowering the usual cheese maturing temperature (15 °C) to 6, 4 or 2 °C. As temperature decreased, A. farris density was drastically reduced from 174 ± 33 mites/cm 2 at the control temperature (15 °C) to 14, 11 and 1 mites/cm 2 for 6, 4 and 2 °C, respectively, though the maturing time was considerably extended. The feasibility of both chemical and physical methods for the control of A. farris is discussed.

Reproduction, longevity and life table parameters of Tyrophagus neiswanderi (Acari: Acaridae) at constant temperatures

The astigmatid mite Tyrophagus neiswanderi Johnston and Bruce is mainly considered a pest of ornamental and horticultural crops. However, this mite has been found infesting Cabrales cheese in Spain, though its population density is low compared to Acarus farris, the prevalent species of astigmatid mite encountered in Cabrales cheese maturing caves. One of the factors that might be influencing this differential abundance is temperature. In the present study the effect of temperature on reproductive parameters and longevity of T. neiswanderi was examined at six constant temperatures, ranging from 10 to 31 degrees C, and a relative humidity of 90 +/- 5%. Preoviposition period, fecundity and daily fecundity were adversely affected by extreme temperatures while the oviposition period increased as temperature was reduced. Male and female longevity increased as temperature decreased, but males showed significantly greater longevity than females. Additionally, this difference was greater as temperature decreased. The effect of temperature on the intrinsic rate of natural increase of T. neiswanderi populations was described by the non-linear Lactin model. The optimum temperature for development was predicted at 26.6 degrees C. At this temperature, the population doubling time is 2.8 days. The lower and upper thresholds for T. neiswanderi populations were calculated at 7.4 and 31.7 degrees C, respectively. According to these results, the influence of temperature on the low population density of this mite found in Cabrales maturing caves compared with A. farris is discussed.

Molecular and Biochemical Properties of Storage Mites (Except Blomia species)

In recent years, the allergological importance of different mite species not belonging to the family Pyroglyphidae has been demonstrated. These mites, commonly named storage mites, include Lepidoglyphus destructor, Glycyphagus domesticus, Tyrophagus putrescentiae, Acarus siro, Aleuroglyphus ovatus, Suidasia medanensis and Thyreophagus entomophagus. Several allergens from these species have been purified, sequenced and cloned. Many of these allergens have shown sequence homology and a biological function similar to those previously described in Blomia tropicalis and the Dermatophagoides spp. The main allergens described in storage mites include fatty acid binding proteins, tropomysin and paramyosin homologues, apoliphorine like proteins, alfa-tubulines and other, such as group 2, 5 and 7 allergens, which definitive biological function has not been described yet. Besides the purification and characterization of allergens, the allergenicity of other species such as Acarus farris, Austroglycyphagus malaysiensis, Blomia kulagini and B. tjibodas, Cheyletus eruditus, Chortoglyphus arcuatus, Gohieria fusca, Thyreophagus entomophagus and Tyrophagus longior has been investigated. Research has also been conducted to identify allergens in parasitic mites, such as Psoroptes ovis, Sarcoptes scabiei, Varroa jacobsoni, Diplaegidia columbae and Hemisarcoptes cooremani. The allergenicity of mites present in agricultural environments has been investigated. Crossreactivity studies have also been performed to elucidate to what extent all these mites share common, or species specific epitopes. Herein we present a comprehensive review of the allergenicity of mite species which have been implicated in human respiratory and/or dermatological diseases.

Evaluation of low humidity treatments to control Acarus farris (Acari: Acaridae) in Cabrales cheese

Laboratory experiments were conducted to establish the best combination of relative humidity (r.h.) and time of exposure to be applied on Cabrales cheeses infested with Acarus farris. Laboratory assays revealed that less than 30 h were required to obtain 90% mortality of mites at 50% and 60% r.h. Males were more susceptible than females to low relative humidity, since their lethal period values (LP) were lower than those obtained for females at the same relative humidity. Moreover, the response within sexes to low moisture treatments changed as exposure time increased, since the LP50 obtained for each sex at 50 and 60% r.h. were statistically different whereas the LP90 showed no significant differences within sexes. Accordingly, two modifications of the traditional maturing process were established to assess the efficacy of low moisture treatments to control A. farris on infested cheeses. The first modification consisted of one single exposure of 48 h at 50% r.h. and the second one consisted of two exposures of 48 h at 50% r.h. separated by a time interval of 15 days. No significant differences in final population density were observed for both low moisture treatments compared to control cheeses. Therefore, low humidity treatments are not effective to control A. farris in Cabrales cheese, despite the good results obtained in laboratory assays.

Effects of relative humidity on development, fecundity and survival of three storage mites

The developmental rate of immature stages and the reproduction of adults of Tyrophagus putrescentiae (Schrank), T. neiswanderi Johnston and Bruce and Acarus farris (Oudemans) were examined at 70, 80 and 90% r.h. and a constant temperature of 25 degrees C. At 70% r.h., T. putrescentiae and A. farris immature stages failed to reach the protonymph stage as 100% of the larvae died, whereas T. neiswanderi was able to complete development. The developmental time of all immature stages for the three species was significantly increased as relative humidity was reduced. The mobile stages were particularly susceptible, as the time needed to complete their development at lower relative humidities suffered greater increases than the egg stage. At 70% r.h., T. putrescentiae and A. farris were not able to lay eggs and only 24% of T. neiswanderi pairs were fertile. The reproductive parameters of the three species at the relative humidities at which they were able to lay eggs showed significant differences, except for the percentage of fertile mating at 80 and 90% r.h. As relative humidity increased, preoviposition period was reduced and fecundity and daily fecundity was increased, whereas the oviposition period showed different patterns for the three species. The intrinsic rate of increase (r ( m )) of T. neiswanderi at 70% r.h. was negative indicating that, at these conditions, mite populations of this species will diminish until they disappear. As relative humidity increased from 80 to 90% r.h. this parameter was almost twofold for both Tyrophagus species. The r ( m ) obtained for A. farris at 90% r.h. was similar to that of T. neiswanderi at the same humidity while at 80% r.h. it was very small so that the population doubling time was more than 84 days. The influence of relative humidity on biology of these mites and its practical application as control measure are discussed.

Effect of temperature on reproductive parameters and the longevity of Acarus farris (Acari: Acaridae)

Reproductive parameters and the longevity of Acarus farris were examined at six constant temperatures, ranging from 7 to 29 °C, and a relative humidity of 90±5%. As temperature increased, the preoviposition period rapidly decreased to a minimum, above 25 °C. Fecundity was adversely affected by extreme temperatures while the oviposition period increased as temperature was reduced. The relationship between reproductive parameters and temperature was fitted using different polynomial and non-linear models. Male and female longevity increased as temperature decreased, except for the males at 7 °C, which showed significantly lower longevity than at 10 °C. Moreover, males showed significantly greater longevity than females. The effect of temperature on the capacity for increase of A. farris populations was also established. The non-linear Lactin model provided a reliable fit of the relationship between intrinsic rate of increase and temperature ( R 2>0.99). The optimum temperature for development was calculated to be 25 °C. At this temperature, the population doubling time was 2.8 days. The lower and upper thermal thresholds for A. farris populations were established at 6.4 and 29.9 °C, respectively.

Comparison of Communities of Stored Product Mites in Grain Mass and Grain Residues in the Czech Republic

In storage facilities one can find grain either in stored grain mass or in grain residues in the store corners or machinery. Although it is claimed that grain residues are serious pest reservoirs since they harbor numbers of stored product arthropods and are connected via continuous emigration with grain mass, the documentation for this is not convincing. Therefore in 78 selected grain stores, we simultaneously sampled the grain mass and residues in order to compare concurrent mite communities in these two different habitats. We found 30 species in about 614,000 individuals in residues and 23 species in about 20 000 individuals in grain mass. Canonical correspondence analysis (CCA) of transformed abundance data showed differences in the communities of mites in grain mass and residues: (i) species associated to grain residues (e.g. Tyrophagus longior, Tydeus interruptus, Acarus farris and Cheyletus eruditus) and (ii) species associated to both grain mass and grain residues (e.g. Tarsonemus granarius, Acarus siro, Tyrophagus putrescentiae, Lepidoglyphus destructor and Cheyletus malaccensis). Although the residue samples had more mites and higher species diversity than the stored grain mass, no correlation in mite abundance and species numbers between samples from grain residues and grain mass was found, thereby indicating low connectivity of these two habitats.

Development and survival of the cheese mites, Acarus farris and Tyrophagus neiswanderi (Acari: Acaridae), at constant temperatures and 90% relative humidity

Two species of acarid mites, Acarus farris and Tyrophagus neiswanderi, have been identified infesting Cabrales cheese in an Asturian maturing cave, the former being the prevalent species. The developmental rate and survival of immature stages of these mites were examined at constant temperatures, ranging from 7 to 29.7 °C for A. farris, and 10 to 31 °C for T. neiswanderi, and a relative humidity (r.h.) of 90±5%. The larval stage of A. farris was particularly susceptible to low and high temperatures with 81.7% and 95.2% mortality at 7 and 29.7 °C, respectively. Tyrophagus neiswanderi larvae also showed the greatest mortality at extreme temperatures among immature stages, though at a lower level than for A. farris (8.6% and 25.6% at 10 and 31 °C, respectively). The optimal temperature for development appeared to be 27–28 °C for both species and the developmental rates were higher for A. farris than T. neiswanderi within the range of the cooler temperatures prevalent in the cheese-maturing caves. The nonlinear Logan type-III model provided the best fit for the relationship between developmental rates and temperature ( R a 2>0.99) for all immature stages of A. farris, whereas the development of T. neiswanderi was better described by the Lactin model ( R a 2>0.97). The lower and upper developmental threshold temperatures predicted for each stage of A. farris were 3–4 °C lower than those predicted for T. neiswanderi. The differential temperature-development rate for each species might explain the greater abundance of A. farris compared to T. neiswanderi. Furthermore, manipulation of temperature based on modeling predictions may well be used to control mite populations during the cheese maturing process.

Some allergenic species of astigmatid mites (Acari, Acaridida) from different synanthropic environments in southern Poland

A survey of allergenic mites from bird nests, farming environments, and from cages and runs of animals of the Silesian ZOO was made. A total of 12,986 mite speci- mens were isolated including 7,570 mites from the order Acaridida (58.3%). The astigma- tid mites were most abundant in farming environments and constituted 67.4% of all mites collected. They formed 46.7% and 58.6% of the total count from bird nests and the Sile- sian ZOO, respectively. More than 29 mite species were identified of which the most abundant were Acarus farris, Acarus immobilis (farms, Silesian ZOO) and Hirstia che- lidonis (bird nests). Caloglyphus oudemansi, the acarid mite species new to the fauna of Poland was found in a cowshed in Majdan Gorny. It is noteworthy that, to the best of our knowledge, samples from zoological garden were actually analysed for the first time on the occurrence of allergenic mites.

Proteolytic activities in body and faecal extracts of the storage mite, Acarus farris

Trypsin, chymotrypsin, cathepsins B and D, aminopeptidase and carboxypeptidases A and B were detected in body extracts of the storage mite Acarus farris (Oudemans) (Astigmata: Acaridae). Faeces-enriched medium exhibited higher (10-50-fold) specific protease activity rates than those measured with mite body extracts for trypsin, chymotrypsin and carboxypeptidases A and B, suggesting that they are involved in mite digestion. However, the activity of cathepsin B was only three-fold higher in faecal than in body extracts, indicating that its presence in the lumen of the digestive tract is low compared to that of serine proteases. The activity of aminopeptidases was higher in mite bodies, indicating that they might be membrane bound. Cathepsin D activity was only detected in body extracts, indicating that this enzyme is not a digestive protease in this species. Zymograms resolved three major bands of gelatinolytic activity, but at least one protease form was only present in body extracts. Protease inhibitors of different specificity were tested in vivo to establish their potential as control agents. The development of A. farris was significantly retarded when the immature stages were fed on artificial diet containing inhibitors of serine and cysteine proteases and aminopeptidases, whereas no such effect was found with inhibitors of aspartyl proteases and carboxypeptidases. Interestingly, the most significant effects on A. farris occurred when a combination of inhibitors targeting different enzyme classes was supplied mixed in the diet, suggesting a synergistic toxicity. Several plant lectins were also tested, but only wheat germ agglutinin and concanavalin-A affected development.

P‐87 Alopecia in two guinea pigs due to hypopodes of Acarus farris

Mites are frequent agents of skin diseases in veterinary dermatology, particularly in rodents. The authors report an original case of infestation in two guinea pigs of the same household. Two adult guinea pigs were presented with a 3‐month history of alopecia, matted hair, erythema, scales and mild pruritus. The first guinea pig showed almost complete truncal alopecia with mild scaling, whereas the other one had only recently developed mild alopecia of the abdomen and mild pruritus. Numerous live, long‐legged mites were present both in adhesive tape and skin scrapings. Mycology (Wood's lamp and DTM agar culture) was negative. Histopathological examination of a skin biopsy did not reveal any significant inflammatory disease and morphological changes were limited to hair follicles in the telogen phase. Mites were identified as hypopodes of Acarus farris (Acaridae), but no adult stages were present. Hypopodes were also found in the hay. Control was obtained with acaricidal treatment with Phoxim 0.05% once weekly for 4 weeks, and the elimination of contaminated hay. The lesions and the alopecia resolved rapidly. Hypopodes are additional nymphal stages of some mites of the suborder Astigmata. They develop for dispersing or dormancy under disadvantageous conditions. They can be active or inert, and some can be phoretic on the skin surface or intrafollicular. Although nonparasitic, they may cause dermatitis. Acarus farris have been rarely mentioned in the literature as a cause of dermatitis. This condition could be underdiagnosed or misdiagnosed in veterinary dermatology. Funding: Self‐funded.

The effect of modified atmospheres on the survival of the eggs of four storage mite species.

The results of a laboratory investigation into the effects of modified atmospheres (MA) on the eggs of mite pests of grain and cheese are presented. Four species of astigmatid mite were tested; Acarus farris (Oudemans). A. siro L., Lepidoglyphus destructor (Schrank) and Tyrophagus longior (Gervais). All are found in many habitats including grain and cheese stores. Three low oxygen (O2) MA mixtures were used, based on carbon dioxide (CO2), nitrogen (N2) or simulated burner gas (0.5 or 2% O2, 10% CO2, balance N2) plus 60% CO2 in air (8% O2). The mites were exposed at 15 degrees C and 80% r.h., a combination of conditions that occurs at the surface of stored grain during the autumn which promotes mite population growth. The exposure periods required to prevent egg hatch for each species in every mixture are given. Tyrophagus longior was the most tolerant species, followed by A. siro and A. farris, with L. destructor the most susceptible. Burner gas was the most effective mixture overall with 0.5% O2 but with an increase in the O2 level to 2% for all the mixtures, CO2 became the more effective control agent. With 60% CO2 in air some loss of efficacy was observed against the three most tolerant species and even more so for L. destructor. Sublethal exposures to MAs for at least 4 days in L. destructor, 6 days in A. farris and A. siro and 8 days for T. longior caused a delay in egg hatch.

Pirimiphos-methyl resistance in two stored product mites, Acarus siro and Acarus farris, as detected by impregnated paper bioassay and esterase activity assays.

The response to pirimiphos-methyl, in one strain of Acarus farris and two strains of Acarus siro, was assessed using an impregnated filter paper bioassay and by the selection of adults following exposure to pirimiphos-methyl. It was concluded that one of the strains of A. siro was resistant to pirimiphos-methyl and that a major resistance mechanism was involved. The second strain of A. siro gave a response similar to that of a laboratory strain unexposed to organophosphates and was considered to be susceptible. The A. farris strain responded to selection at the ED50 but not at the ED99, and it was concluded that a minor resistance mechanism is present in this strain. Assays of esterase activity were used to attempt to identify the biochemical mechanisms involved in the resistance detected by the bioassays. The A. farris and susceptible A. siro strains showed similar levels of esterase activity but the esterase activity of the resistant A. siro strain was significantly greater. An increase in esterase activity followed selection of both the A. farris strain and the resistant A. siro strain. An acetylcholinesterase assay showed no significant difference between the susceptible and pirimiphos-methyl selected strains of A. siro. The results suggest that esterases are involved in the resistance to pirimiphos-methyl found in A. siro and A. farris but that in A. siro, at least, other mechanisms may also be present.