Short term transcriptional responses of P450s to phytochemicals in insects and mites

Cytochrome P450 monooxygenases (P450s) play a key role in the detoxification of phytochemicals in arthropod herbivores. We present here an overview of recent progress in understanding the breadth and specificity of gene expression plasticity of P450s in response to phytochemicals. We discuss experimental setups and new findings in mechanisms of P450 regulation. Whole genome transcriptomic analysis of arthropod herbivores, either after direct administration of phytochemicals or after host plant shifts, allowed to integrate various levels of chemical complexity and lead to the unbiased identification of responsive P450 genes. However, despite progress in identification of inducible P450s, the link between induction and metabolism is still largely unexplored, and to what extent the overall response is biologically functional should be further investigated. In the near future, such studies will be more straightforward as forward and reverse genetic tools become more readily available.

Integrative taxonomy of Abacarus mites (Eriophyidae) associated with hybrid sugarcane plants, including description of a new species

Phytophagous mites belonging to the Eriophyoidea are extremely diverse and highly host-specific. Their accurate morphological identification is hampered by their reduced size and simplified bodies and by the existence of cryptic species complexes. Previous studies have demonstrated the urgency of applying multisource methods to accurate taxonomic identification of eriophyoid mites, especially species belonging to the genus Abacarus. This genus comprises 65 species, of which 37 are associated with grasses and four with sugarcane Saccharum (Poaceae). Recently, Abacarus specimens very similar to Abacarus sacchari were collected from the sugarcane crop in Brazil; however, their taxonomic placement was uncertain. In this study, we used an integrative approach to determine whether A. aff. sacchari specimens belong to A. sacchari or constitute a cryptic species. Morphological data were combined with molecular phylogeny based on the nucleotide sequences of three markers, one mitochondrial (COI) and two nuclear (D2 region of 28S and ITS). Morphological differences were observed between A. aff. sacchari, A. sacchari and A. doctus. The phylogenetic relationships among these three taxa and the genetic distances separating them revealed an interspecific divergence. The results of the morphological and molecular methods were congruent and supported the existence of a new species: Abacarus neosacchari n. sp. Duarte and Navia, herein described. This species belongs to the Abacarus cryptic species complex associated with sugarcane in the Americas. The results of this study, presenting the occurrence of multiple Abacarus species associated with sugarcane, contribute to the knowledge on plants and mites diversity by adding up one more clue highlighting that plant hybridization can be an important mechanism contributing to the speciation of plant-feeding arthropods.

Effects of UV-B radiation on the survival, egg hatchability and transcript expression of antioxidant enzymes in a high-temperature adapted strain of Neoseiulus barkeri

Biological control of spider mites in hot and dry weather is a serious technical issue. A high-temperature adapted strain (HTAS) of the predatory mite Neoseiulus barkeri Hughes was selected from its conventional strain (CS), via long-term heat acclimation and frequent heat hardenings in our previous studies. However, the environment of high temperature is usually associated with enhanced ultraviolet (UV) radiation. In the present study, the physiological effects of UV-B radiation on survival rate and egg damage of N. barkeri were investigated, as well as the activities and expression profiles of antioxidant enzymes to UV-B radiation stress. UV-B radiation had deleterious effects on egg hatchability and survival of N. barkeri. Adults of the HTAS strain were less UV-B resistant than those of the CS strain; they also had lower levels of enzymatic activity of superoxide dismutase (SOD) and catalase against oxidative damage and weaker upregulation of SOD genes. The mRNA expression of three SOD genes of CS adult females immediately increased whereas that of HTAS showed almost no difference under UV-B stress for 1 h. The results showed the HTAS of N. barkeri had lower fitness under UV-B stress compared with the CS of N. barkeri. These results suggested that long-term heat acclimation may exert a profound impact on the developmental physiology of N. barkeri.

The genetic structure of hypoderatid mites (Actinotrichida: Astigmata) parasitizing great cormorant (Phalacrocorax carbo) during host post-breeding dispersal in Milicz, SW Poland

The astigmatid family Hypoderatidae includes over 80 mite species exhibiting peculiar life cycle. Deutonymphs are parasitic instars inhabiting subcutaneous or visceral tissues of birds and rodents, while all other instars are nidicolous forms. In this study we investigated genetic diversity of deutonymphs of two hypoderatid species, Neottialges evansi and Phalacrodectes gaudi, collected from 16 individuals of the great cormorant Phalacrocorax carbo in SW Poland during host post-breeding dispersal. The initial alternative hypotheses were: (1) populations of deutonymphs in both mite species found in tissues of particular bird individuals form genetically distinct populations, (2) mites are panmictic among hosts. The topologies of NJ phylogenetic trees and median-joining haplotype networks reconstructed for COI haplotypes revealed lack of hostdependent genetic structure in populations of N. evansi and P. gaudi. Furthermore, high haplotype diversity (Hd) and low nucleotide diversity (Pi) prove high genetic differentiation of both mite species. We concluded, that unlimited dispersal of mites among cormorant specimens could be explained by host specific breeding behavior: free mating between cormorants originating from different European populations and low contribution of reunited pairs in breeding colonies in subsequent breeding seasons, reuse of the same nest material by different members of the colony, and host behavior called prospecting.

Analysis of Genetic Variation in Brevipalpus yothersi (Acari: Tenuipalpidae) Populations from Four Species of Citrus Host Plants

We studied species diversity and genetic variation among populations of Brevipalpus mites from four species of citrus host plants. We sampled mites on orange, lime, grapefruit and mandarin trees from orchards at six localities distributed in the five most important citrus producing states in Mexico. Genetic variation among citrus host plants and localities were assessed by analysis of nucleotide sequence data from fragments of the mitochondrial cytochrome oxidase subunit I (COI). Both Brevipalpus yothersi and B. californicus were found at these sites, and B. yothersi was the most abundant species found on all citrus species and in all localities sampled. B. californicus was found mainly on orange and mandarin and only in two of the states sampled. AMOVA and haplotype network analyses revealed no correlation between B. yothersi genetic population structure and geographical origin or citrus host plant species. Considering that a previous study reported greater genetic diversity in B. yothersi populations from Brazil than we observed in Mexico, we discuss the possibility that the Mexican populations may have originated in the southern region of America.

The Glutathione-S-Transferase, Cytochrome P450 and Carboxyl/Cholinesterase Gene Superfamilies in Predatory Mite Metaseiulus occidentalis

Pesticide-resistant populations of the predatory mite Metaseiulus (= Typhlodromus or Galendromus) occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) have been used in the biological control of pest mites such as phytophagous Tetranychus urticae. However, the pesticide resistance mechanisms in M. occidentalis remain largely unknown. In other arthropods, members of the glutathione-S-transferase (GST), cytochrome P450 (CYP) and carboxyl/cholinesterase (CCE) gene superfamilies are involved in the diverse biological pathways such as the metabolism of xenobiotics (e.g. pesticides) in addition to hormonal and chemosensory processes. In the current study, we report the identification and initial characterization of 123 genes in the GST, CYP and CCE superfamilies in the recently sequenced M. occidentalis genome. The gene count represents a reduction of 35% compared to T. urticae. The distribution of genes in the GST and CCE superfamilies in M. occidentalis differs significantly from those of insects and resembles that of T. urticae. Specifically, we report the presence of the Mu class GSTs, and the J’ and J” clade CCEs that, within the Arthropoda, appear unique to Acari. Interestingly, the majority of CCEs in the J’ and J” clades contain a catalytic triad, suggesting that they are catalytically active. They likely represent two Acari-specific CCE clades that may participate in detoxification of xenobiotics. The current study of genes in these superfamilies provides preliminary insights into the potential molecular components that may be involved in pesticide metabolism as well as hormonal/chemosensory processes in the agriculturally important M. occidentalis.

Characteristics of carboxylesterase genes and their expression-level between acaricide-susceptible and resistant Tetranychus cinnabarinus (Boisduval)

Carboxylesterases (CarEs) play important roles in metabolism and detoxification of dietary and environmental xenobiotics in insects and mites. On the basis of the Tetranychuscinnabarinus transcriptome dataset, 23 CarE genes (6 genes are full sequence and 17 genes are partial sequence) were identified. Synergist bioassay showed that CarEs were involved in acaricide detoxification and resistance in fenpropathrin- (FeR) and cyflumetofen-resistant (CyR) strains. In order to further reveal the relationship between CarE gene's expression and acaricide-resistance in T. cinnabarinus, we profiled their expression in susceptible (SS) and resistant strains (FeR, and CyR). There were 8 and 4 over-expressed carboxylesterase genes in FeR and CyR, respectively, from which the over-expressions were detected at mRNA level, but not DNA level. Pesticide induction experiment elucidated that 4 of 8 and 2 of 4 up-regulated genes were inducible with significance in FeR and CyR strains, respectively, but they could not be induced in SS strain, which indicated that these genes became more enhanced and effective to withstand the pesticides' stress in resistant T. cinnabarinus. Most expression-changed and all inducible genes possess the Abhydrolase_3 motif, which is a catalytic domain for hydrolyzing. As a whole, these findings in current study provide clues for further elucidating the function and regulation mechanism of these carboxylesterase genes in T. cinnabarinus' resistance formation.

Northern fowl mite (Ornithonyssus sylviarum) in Sweden

Haematophagous mites were collected from the vent region and plumage of chickens in six hobby flocks of ornamental breeds in Sweden, one of which included turkeys. Soiled vent skin and feathers, dermatitis, hyperkeratosis, skin necroses and ulcers were observed in 12 necropsied birds from two of the flocks. The mites were identified as the northern fowl mite Ornithonyssus sylviarum (Mesostigmata: Macronyssidae). This was supported by sequence analysis of a 642-bp region in the mitochondrial cytochrome oxidase subunit 1 (COI) gene (COI) in mites collected from five flocks, which showed 97-99% sequence similarity to O. sylviarum by blast analysis. Pairwise sequence comparisons revealed nucleotide variations in the range of 0-2.8%, whereas amino acid sequences were highly conserved. This paper represents one of very few records of O. sylviarum in European poultry, and is the first to report COI sequence data for O. sylviarum from poultry in Europe.

Effects of heat stress on development, reproduction and activities of protective enzymes in Mononychellus mcgregori

Mononychellus mcgregori is a pest mite of cassava. Since its invasion into China in 2008 it has spread rapidly. In order to determine the potential distribution and to analyze its invasion, diffusion and ecological adaptation mechanisms, we investigated the effect of high-temperature stress (30, 33, 36, 39 and 42 °C) on its development and reproduction, and the activity of protective enzymes in the mite. The results indicated significant influences: (1) adults could not lay eggs after they had been exposed to 42 °C for 4 h or longer; (2) egg development was slower and egg hatchability decreased after exposure of adults to 33-42 °C for 1 h; (3) offspring development (all stages) was slower after exposure of adults to 33-42 °C for 2 h or more; and (4) polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT) activities in the adults increased to high levels after exposure to 33-42 °C for 1 h, and superoxide dismutase activity increased only after exposure to 42 °C for 1 h. In conclusion, exposure to high temperatures for only 1 h probably has an important impact on the mite's population growth. The significant increase of PPO, POD, APX, and CAT activities in adults may partially explain how M. mcgregori survive exposure to a relatively high temperature.

Determination of the inheritance, cross-resistance and detoxifying enzyme levels of a laboratory-selected, spiromesifen-resistant population of the predatory mite Neoseiulus californicus (Acari: Phytoseiidae)

BACKGROUND

Neoseiulus californicus of the family Phytoseiidae is an effective predatory mite species that is used to control pest mites.

RESULTS

The LC50 and LC60 values of spiromesifen were determined on N. californicus using a leaf-disc method and spraying tower. A laboratory selection population designated SPR13 was found to have a 52.08-fold resistance to spiromesifen following 13 selection cycles. This population developed low resistance to hexythiazox and moderate cross-resistance to propargite, clofentezine, spirodiclofen, etoxazole and milbemectin. PBO, IBP and DEM synergised resistance 3.75-, 2.54- and 1.93-fold respectively. Crossing experiments revealed that spiromesifen resistance in the SPR13 population was intermediately dominant and monogenic. In addition, detoxifying enzyme activities were increased 2.74-fold for esterase, 3.09-fold for glutathione S-transferase and 2.17-fold for cytochrome P450 monooxygenase in the SPR13 population.

CONCLUSIONS

Selection for spiromesifen under laboratory conditions resulted in the development of spiromesifen resistance in the predatory mite N. californicus. Predatory mites that are resistant to pesticides are considered valuable for use in resistance management programmes within integrated pest control strategies.

Effects of thermal stress on lipid peroxidation and antioxidant enzyme activities of the predatory mite, Neoseiulus cucumeris (Acari: Phytoseiidae)

Changes in temperature are known to cause a variety of physiological stress responses in insects and mites. Thermal stress responses are usually associated with the increased generation of reactive oxygen species (ROS), resulting in oxidative damage. In this study, we examined the time-related effect (durations for 1, 2, 3, and 5 h) of thermal stress conditions-i.e., relatively low (0, 5, 10, and 15 °C) or high (35, 38, 41, and 44 °C) temperatures-on the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), glutathione S-transferases (GSTs), and total antioxidant capacity (T-AOC) of the predatory mite Neoseiulus cucumeris. Also the lipid peroxidation (LPO) levels of the predatory mite were measured under thermal stress conditions. The results confirmed that thermal stress results in a condition of so-called oxidative stress and the four antioxidant enzymes play an important role in combating the accumulation of ROS in N. cucumeris. CAT and POX activity changed significantly when the mites were exposed to cold and heat shock, respectively. The elevated levels of SOD and GSTs activity, expressed in a time-dependent manner, may have an important role in the process of antioxidant response to thermal stress. However, the levels of LPO in N. cucumeris were high, serving as an important signal that these antioxidant enzyme-based defense mechanisms were not always adequate to counteract the surplus ROS. Thus, we hypothesize that thermal stress, especially extreme temperatures, may contribute much to the generation of ROS in N. cucumeris, and eventually to its death.

Expression of a barley cystatin gene in maize enhances resistance against phytophagous mites by altering their cysteine-proteases

Phytocystatins are inhibitors of cysteine-proteases from plants putatively involved in plant defence based on their capability of inhibit heterologous enzymes. We have previously characterised the whole cystatin gene family members from barley (HvCPI-1 to HvCPI-13). The aim of this study was to assess the effects of barley cystatins on two phytophagous spider mites, Tetranychus urticae and Brevipalpus chilensis. The determination of proteolytic activity profile in both mite species showed the presence of the cysteine-proteases, putative targets of cystatins, among other enzymatic activities. All barley cystatins, except HvCPI-1 and HvCPI-7, inhibited in vitro mite cathepsin L- and/or cathepsin B-like activities, HvCPI-6 being the strongest inhibitor for both mite species. Transgenic maize plants expressing HvCPI-6 protein were generated and the functional integrity of the cystatin transgene was confirmed by in vitro inhibitory effect observed against T. urticae and B. chilensis protein extracts. Feeding experiments impaired on transgenic lines performed with T. urticae impaired mite development and reproductive performance. Besides, a significant reduction of cathepsin L-like and/or cathepsin B-like activities was observed when the spider mite fed on maize plants expressing HvCPI-6 cystatin. These findings reveal the potential of barley cystatins as acaricide proteins to protect plants against two important mite pests.

Molecular phylogenetic assessment of host range in five Dermanyssus species

Given that 14 out of the 25 currently described species of Dermanyssus Dugès, 1834, are morphologically very close to each another, misidentifications may occur and are suspected in at least some records. One of these 14 species is the red fowl mite, D. gallinae (De Geer, 1778), a blood parasite of wild birds, but also a pest in the poultry industry. Using molecular phylogenetic tools we aimed to answer two questions concerning host specificity and synanthropicity: (1) is D. gallinae the only species infesting European layer farms?, and (2) can populations of D. gallinae move from wild to domestic birds and vice versa? Mitochondrial cytochrome oxidase I gene sequences were obtained from 73 Dermanyssus populations collected from nests of wild European birds and from poultry farms and these were analyzed using maximum parsimony and Bayesian inference. Mapping of the observed host range on the obtained topology and correlation with behavioural observations revealed that (1) host range is strongly dependent on some ecological parameters (e.g. nest hygiene, exposure to pesticides and predators), that (2) out of five species under test, synanthropic populations were found only in lineages of D. gallinae, and that (3) at least some haplotypes found in wild birds were very close to those found in association with domestic birds.

Exploration of the susceptibility of AChE from the poultry red mite Dermanyssus gallinae (Acari: Mesostigmata) to organophosphates in field isolates from France

The red fowl mite Dermanyssus gallinae (De Geer, 1778) is a hematophagous mite species, which is very commonly found in layer facilities in Europe. The economic and animal health impact of this parasite is quite important. In laying hen houses, organophosphates are almost the only legally usable chemicals. Detecting a target resistance can be useful in order to limit the emergence of resistant populations. The acetylcholinesterase (AChE) activity and the enzyme sensitivity to paraoxon was investigated in 39 field samples and compared to a susceptible reference strain (SSK). Insensitivity factor values (expressed as IC50 ratio) obtained from field isolates compared to SSK revealed some polymorphism but not exceeding a 6-fold difference. The kinetic characteristics of AChE from some field samples showed some difference in KM values for acetylthiocholine and inhibition kinetics performed with diethyl paraoxon exhibited a 5.5-fold difference in the bimolecular rate constant in one field isolate. Taken together, these data suggested that differences in AChE susceptibility to organophosphates may exist in D. gallinae but no resistant population was found.

Resistance mechanisms to mitochondrial electron transport inhibitors in a field-collected strain of Tetranychus urticae Koch (Acari: Tetranychidae)

A Belgian field strain (MR-VP) of Tetranychus urticae (Koch) (Acari: Tetranychidae) exhibits different levels of resistance to four frequently used METI (mitochondrial electron transport inhibitor)-acaricides, i.e. tebufenpyrad, fenpyroximate, pyridaben and fenazaquin. Resistance factors for these compounds were 184, 1547, 5971 and 35, respectively. A 23.5-fold increase in 7-ethoxy-4-trifluoromethylcoumarin O-deethylation activity suggested that metabolic resistance through elevated levels of cytochrome P450 dependent monooxygenase-activity is a possible resistance mechanism.However, synergism studies with different metabolic inhibitors revealed some contrasting resistance mechanisms between the METI-acaricides. Tebufenpyrad resistance could only be synergized after pre-treatment with the monooxygenase inhibitor piperonyl butoxide (PBO), whereas pyridaben resistance was strongly synergized both by PBO and the esterase inhibitor S,S,S-tributylphosphorotrithioate (DEF). Resistance levels to fenpyroximate could neither be suppressed by PBO nor by DEF. Although METI-acaricides are structurally related, these findings probably reflect a different role of esterases and mono-oxygenases in metabolic detoxification between these compounds. The overall lack of synergism by diethylmaleate (DEM) suggests that glutathione-S-transferases are not an important factor in resistance to METIs.Reciprocal crosses between susceptible females and resistant males showed no maternal effect, and resistance to METI-acaricides was inherited generally as a dominant trait. Backcrosses with F1 females revealed striking differences in the mode of inheritance. Although resistance to fenpyroximate and pyridaben was under monogenic control, resistance to tebufenpyrad was under control of more than one gene.

Digestive function of lysozyme in synanthropic acaridid mites enables utilization of bacteria as a food source

The activity of lysozyme, the enzyme that hydrolyzes peptidoglycan in G(+) bacterial cell walls, was detected in whole mite extracts (WME) and in spent growth medium extracts (SGME) of 14 species of synanthropic mites (Acari: Acaridida). The adaptation of lysozyme for digestive activity and bacteriophagy was based on: (i) high lysozyme activity in SGME, and (ii) the correlation of maximum lysozyme activity at acidic pH values, corresponding to pH in the ventriculus and caeca. We show that the digestion of fluorescein-labeled Micrococcus lysodeikticus cells began in ventriculus and continued during the passage of a food bolus through the gut. The fluorescein was absorbed by midgut cells and penetrated to parenchymal tissues. Eight species showed a higher rate of population growth on a M. lysodeikticus diet than on a control diet. The lysozyme activity in SGME was positively correlated to the standardized rate (r (s)) of population growth, although no correlation was found between r (s) and lysozyme activity in WME. The lysozyme activity in WME was negatively correlated to that in SGME. The highest activity of digestive lysozyme was found in Lepidoglyphus destructor, Chortoglyphus arcuatus and Dermatophagoides farinae. All of these findings indicate that lysozyme in acaridid mites possesses both defensive and digestive functions. The enzymatic properties of mite lysozyme are similar to those of the lysozymes present in the ruminant stomach and in the insect midgut.

Enzymatic Activity in Body and Fecal Extracts of the Storage Mite Chortoglyphus arcuatus

BACKGROUND

Chortoglyphus arcuatus has been described in many countries. Many allergens are potent enzymes, which may promote a Th2 immune response. The aim of this study was to evaluate the enzymatic activity of body and fecal extracts of C. arcuatus.

MATERIAL AND METHODS

Feces and bodies of full-grown C. arcuatus cultures were separated by sieving, extracted in PBS, dialyzed and lyophilized. The antigenic profile of both extracts was determined by SDS-PAGE. Immunoblot experiments were conducted using a pool of sera from allergic individuals residing in Galicia, a region of Spain, where this species is abundant. The enzymatic activity of the extracts was evaluated by the zymogram technique. Serine and cysteine protease activity was measured using in vitro methods. The API Zym system was used to determine the enzymatic properties of the extracts.

RESULTS

The antigenic profile showed that the body extract contained more and better defined bands than the fecal extract. Allergens were detected in both extracts in a molecular weight range between 14 and 100 kDa. Gelatinolytic gels confirmed that fecal extracts contain more hydrolytic enzymatic activity than body extracts. Serine protease activity in fecal extracts was higher than in body extracts (5.98 vs. 2.701 IU of trypsin/mg of freeze-dried material). No cysteine protease activity was detected.

CONCLUSION

C. arcuatus extracts contain several allergens and proteins with high enzymatic activity, especially in the feces. Some of these allergens may be enzymes. Fecal extracts have more enzymatic activity than body extracts.

Enzymatic activity in extracts of allergy-causing astigmatid mites

Many of the previously characterized allergens of house dust mites are known to be proteases, and this enzymatic activity is thought to contribute to their allergenicity. Other astigmatid mites, including stored-product mites and the ectoparasitic itch mite, Sarcoptes scabiei De Geer, are also known to be allergenic, but little or nothing is known about their enzymatic activities. The purpose of this study was to characterize the enzymatic activities present in extracts of the parasitic itch mite and from eight other species of free-living astigmatid mites. Extracts were prepared from one parasitic mite (S. scabiei), five stored-product mites (Chortoglyphus arcuatus (Troupeau), Lepidoglyphus destructor (Schrank), Blomia tropicalis Bronswijk, Cock, Oshima, Tyrophagus putrescentiae (Schrank), and Acarus siro L.), and three house dust mites [Dermatophagoidesfarinae Hughes, Dermatophagoides pteronyssinus (Troussart), and Euroglyphus maynei (Cooreman) ]. ApiZym strips were used to screen for the presence of 19 individual enzyme activities. Digestion of nine other substrates was evaluated by spectrophotometric or electrophoretic methods. All mite extracts exhibited some form of phosphatase, esterase, aminopeptidase, and glycosidase activity, although their substrate specificities varied considerably. Itch mite extract did not possess detectable serine peptidase activity nor was it able to hydrolyze gelatin or casein, whereas all other mite extracts exhibited these activities. Storage mite extracts possessed enzymes capable of degrading the widest range of substrates, whereas itch mite extract had the most limited proteolytic capacity. Extracts of nine species of allergy-causing astigmatid mites contain wide and diverse repertoires of enzymatic activities. These catalytic activities may be important contributors to the induction and manifestation of inflammatory and immune responses to mites in patients.

Strong association between a single gene and fertilization efficiency of males and fecundity of their mates in the bulb mite

Although variation in male fertilization efficiency has been shown to have a genetic basis in several species, the genes responsible for the effect are generally unknown. Here, we show a strong association between the fertilization success of males and their phosphogluconate dehydrogenase (Pgdh) genotype in the bulb mite Rhizoglyphus robini. Males homozygous for the slow (S) allele fathered a significantly greater proportion of offspring when competing with males homozygous for the fast (F) allele. There was no evidence that female fecundity was influenced by their Pgdh genotype. The fecundity of FF females did not differ significantly from the fecundity of SS females but female fecundity was significantly influenced by the genotype of their mate. Females paired with SS males laid significantly fewer eggs than females paired with FF males. Altogether these data show a trade-off, with the male SS genotype associated with their higher fertilization efficiency but at the cost of a negative impact on the fecundity of females mating with them.

Monooxygenase activity in methidathion resistant and susceptible populations of Amblyseius womersleyi (Acari: Phytoseiidae)

The purpose of this study was to evaluate the cytochrome P450-dependent monooxygenase activities in methidathion resistant and susceptible strains of Amblyseius womersleyi Schicha. Artificial laboratory selections for resistance and susceptibility to methidathion were performed in an organophosphate resistant strain of A. womersleyi (Kanaya strain). Selections for susceptibility were also performed in a susceptible strain of this predaceous mite (Ishigaki Strain). After the selection process, the LC(50) of methidathion for the selected strains of A. womersleyi were 816 mg/l (Kanaya R), 4.61 mg/l (Kanaya S) and 1.59 mg/l (Ishigaki S). The monooxygenase activities were determined biochemically by the O-deethylation of 7-ethoxycoumarin (7-EC). The monooxygenase activity in adult females of Kanaya R strain (51.1 pmol/30 min/mg protein) was 3.60- and 5.42-fold higher than the activity observed for Kanaya S and Ishigaki S strains, respectively. Significant correlation between monooxygenase activity and LC(50) (mg/l) of methidathion was observed analyzing 16 populations of A. womersleyi with different susceptibilities to methidathion. Monooxygenase activity was also evaluated in different life stages (egg, larva, protonymph, deutonymph and adult) of A. womersleyi. The lowest activity was observed for the larval stage, which presented the highest susceptibility to methidathion. Protonymph, deutonymph and adult presented the highest monooxygenase activities. These stages were the most tolerant to methidathion. Monooxygenase activities of the Kanaya R strain were higher than of the Kanaya S strain in all developmental stages. The present study can be helpful for the implementation of a program involving release of insecticide-resistant populations of A. womersleyi in the field. The monooxygenase activity determination is easier and quicker than the estimation of LC(50), requiring fewer mites.

Enzymatic analysis of Blomia tropicalis and Blomia kulagini (Acari: Echimyopodidae) allergenic extracts obtained from different phases of culture growth

The majority of important allergenic extracts from arthropods present enzymatic activity. This activity has been studied particularly in Dermatophagoides house dust mites because of its implication in the stability and immunogenicity of extracts used as tools for the diagnosis and specific treatment of allergic diseases. Extracts from cultures of Blomia tropicalis [van Bronswijk (1973a, b). Acarologia 15:477-489, 490-505] and Blomia kulagini (Zakhvatkin 1936) were used to study enzymatic profiles during three growth periods of the mite population: latency phase, maximum mite concentration during exponential growth, and drop stage. The activities of 19 enzymes were analyzed using the Api Zym system. The results show a large variety of enzymes. Some enzymatic activity was found to be (almost) exclusively attributable to mites. The activity levels of proteases, glycosidases and lipases overlapped with the growth curve. Only phosphatase activity showed no significant change during mite growth when compared with the culture medium. We suggest that the glycosidases (beta-galactosidase, beta-glucuronidase, beta-N-acetylglucosaminidase, alpha-mannosidase and alpha-fucosidase) and proteases (leucine aminopeptidase and trypsin) may constitute suitable parameters for inclusion in the quality control process for the production of allergenic mite extracts, and may help define a new index for conducting environmental controls.

Comparing the organophosphorus and carbamate insecticide resistance mutations in cholin- and carboxyl-esterases

Mutant insect carboxyl/cholinesterases underlie over 60 cases of resistance to organophosphorus and/or carbamate insecticides. Biochemical and molecular data on about 20 of these show recurrent use of a very small number of mutational options to generate either target site or metabolic resistance. Moreover, the mutant enzymes are often kinetically inefficient and associated with significant fitness costs, due to impaired performance of the enzymes' original function. By contrast many bacterial enzymes are now known which can effectively detoxify these pesticides. It appears that the constraints of the genetic code and eukaryote genetic systems have severely limited the evolutionary response of insects to the widespread use of the insecticides over the last 60 years.

Potential roles in rhinitis for protease and other enzymatic activities of allergens

Exposure to airborne pollen, fungal allergens, and dust mite allergens is associated with the development of allergic rhinitis. Biologic function of allergens is considered to be a key determinant for allergenicity, and many clinically important allergens have been shown to possess enzymatic activity. It is proposed that by enabling allergens to breach the integrity of the airway epithelial barrier, proteolytic activity plays an adjuvant pro-allergic role influencing immunogenicity. In this review, current evidence regarding enzymatic activity of aeroallergens is described, and the potential role of aeroallergens in allergic rhinitis is discussed.

Inhibitory specificity and insecticidal selectivity of alpha-amylase inhibitor from Phaseolus vulgaris

The primary structure and proteolytic processing of the alpha-amylase isoinhibitor alpha AI-1 from common bean (Phaseolus vulgaris cv. Magna) was determined by protein chemistry techniques. The inhibitory specificity of alphaAI-1 was screened with a panel of the digestive alpha-amylases from 30 species of insects, mites, gastropod, annelid worm, nematode and fungal phytopathogens with a focus on agricultural pests and important model species. This in vitro analysis showed a selective inhibition of alpha-amylases from three orders of insect (Coleoptera, Hymenoptera and Diptera) and an inhibition of alpha-amylases of the annelid worm. The inhibitory potential of alphaAI-1 against several alpha-amylases was found to be modulated by pH. To understand how alphaAI-1 discriminates among closely related alpha-amylases, the sequences of the alpha-amylases sensitive, respectively, insensitive to alphaAI-1 were compared, and the critical determinants were localized on the spatial alpha-amylase model. Based on the in vitro analysis of the inhibitory specificity of alphaAI-1, the in vivo activity of the ingested alphaAI-1 was demonstrated by suppression of the development of the insect larvae that expressed the sensitive digestive alpha-amylases. The first comprehensive mapping of alphaAI-1 specificity significantly broadens the spectrum of targets that can be regulated by alpha-amylase inhibitors of plant origin, and points to potential application of these protein insecticides in plant biotechnologies.

In vitro and in vivo inhibition of alpha-amylases of stored-product mite Acarus siro

The stored-product mites are the most abundant and frequent group of pests living on the stored food products in Europe. They endanger public health since they produce allergens and transmit mycotoxin-producing fungi. Novel acaricidal compounds with inhibitory effects on the digestive enzymes of arthropods are a safe alternative to the traditional neurotoxic pesticides used for control of the stored-product pests. In this work, we explored the properties of acarbose, the low molecular weight inhibitor of alpha-amylases (AI), as a novel acaricide candidate for protection of the stored products from infestation by Acarus siro (Acari: Acaridae). In vitro analysis revealed that AI blocked efficiently the enzymatic activity of digestive amylases of A. siro, and decreased the physiological capacity of mite's gut in utilizing a starch component of grain flour. In vivo experiments showed that AI suppressed the population growth of A. siro. The mites were kept for three weeks on experimental diet enriched by AI in concentration range of 0.005 to 0.25%. Population growth of A. siro was negatively correlated with the content of AI in the treated diet with a half-population dose of 0.125%. The suppressive effect of AIs on stored-product mites is discussed in the context of their potential application in GMO crops.

Sequence of a cDNA encoding acetylcholinesterase from susceptible and resistant two-spotted spider mite, Tetranychus urticae

Acetylcholinesterase (AChE) from two-spotted spider mites, Tetranychus urticae was compared between an organophosphate susceptible (TKD) and a resistant (NCN) strain. The AChE of TKD had lower affinity to acetylthiocholine and propionylthiocholine than that of NCN, and the inhibition of AChE by DDVP, ambenonium, eserine and n-methyl-eserine showed that NCN was more insensitive than TKD. AChE cDNA sequence was determined, and the 687 amino acids of primary structure were deduced. There were six replacements of amino acid residues in TKD and two in NCN. #F331(439)C was the only substitution unique to NCN, however, this mutation existed homozygously in only two out of nine mites. This residue is one of the gorge lining components, and #F331(439)C might act an important role in the sensitivity of AChE to the inhibitors.

Characterisation of aminopeptidase activity in scab mites (Psoroptes spp.)

Soluble and membrane-bound aminopeptidase activities were demonstrated in extracts of P. cuniculi (Delafond). Leucine aminopeptidase (LAP) activity in the soluble fraction of P. cuniculi extracts displayed substrate preference for amino acid derivatives with terminal leucine and methionine over those with acidic, basic or heterocyclic groups. P. cuniculi LAP was inhibited by leucinethiol (IC(50) = 1.4 +/- 0.4 nM), bestatin (IC(50) = 3.9 +/- 1.7 microM), Arphamenine A (IC(50) = 0.37 +/- 0.03 mM) the chelating agent 1,10-phenanthroline (IC(50) = 2.3 +/- 0.5 mM), Zn(2+), Cu(2+) Ni(2+), and Co(2+), and activated by Mn(2+) and Mg(2+). The LAP activity was visualised as a single major band after electrophoresis on native gels and eluted from a size exclusion column as a single major peak representing a molecular mass range of 85-116 kDa. Degenerate oligonucleotide primers were used to amplify short fragments of genomic DNA containing nucleotide sequence coding for the cation-binding motifs of the co-catalytic Zn(2+) binding domains of dizinc leucine aminopeptidases in both P. cuniculi and P.ovis (Hering). The major soluble aminopeptidase from these mites therefore displays most of the characteristics associated with typical cytosolic leucine aminopeptidases belonging to the M17 family of metalloproteinases.

Isolation and characterisation of a 13.8-kDa bacteriolytic enzyme from house dust mite extracts: homology with prokaryotic proteins suggests that the enzyme could be bacterially derived

Bacteriolytic activity was detected in extracts of whole mite and spent growth medium (SGM) from the clinically important Dermatophagoides pteronyssinus and Dermatophagoides farinae mites and was most abundant in whole mite extract. Gram-positive organisms Micrococcus lysodeikticus, Bacillus megaterium and Listeria monocytogenes were preferentially lysed and the lytic activity was enhanced by thiols, destroyed by mite proteases, inhibited by HgCl2 and high concentrations of NaCl but was resistant to heat and acid treatment. Substrate SDS-PAGE analysis indicated the presence of several lytic enzymes, two of which were isolated from D. pteronyssinus spent growth medium extract by hydroxyapatite chromatography. The N-terminal amino acid sequence of one of them was then used in PCR-based cloning studies. The complete amino acid sequence of this protein was determined and cDNA found to encode a 130-amino acid residue mature protein with a 20-amino acid leader sequence. The deduced protein demonstrated sequence similarity with the C-terminal regions of a group of bacterial proteins belonging to the P60 superfamily. These data suggest that the enzyme is derived from bacteria within the mites rather than from mites per se.

The proteinases of Psoroptes ovis, the sheep scab mite--their diversity and substrate specificity

The sheep scab mite, Psoroptes ovis, causes severe dermatitis in infected sheep with severe welfare and production implications. The dermatitis has the characteristics of an immediate hypersensitivity type reaction which, by analogy to other mite species, including the house dust mites (Dermatophagoides spp.), is likely to be invoked by a variety of allergens including mite-derived proteinases. Here, the proteinases in P. ovis extracts were characterised using substrate gel analysis, inhibitor sensitivity and their ability to degrade a variety of potential natural protein substrates. These analyses showed that mites contain several proteinases which could be differentiated on the basis of molecular size and inhibitor sensitivity with cysteine, metalloproteinases and aspartyl proteinases predominating. These proteinases degraded collagen and fibronectin, possibly indicative of a role in lesion initiation, they degraded several blood proteins, a property which may aid mite feeding and they degraded immunoglobulin G, possibly aiding immuno-evasion. Because proteinases, particularly the cysteine class, are demonstrably allergenic in other mite infestations, these proteinases clearly merit further immunological and biochemical definition.

Expression and characterisation of a Psoroptes ovis glutathione S-transferase

The astigmatid mite Psoroptes ovis is the causative agent of sheep scab, a highly contagious parasitic disease of sheep. Infection causes severe allergic dermatitis, resulting in damage to the fleece and hide, loss of condition and occasional mortality. Interest in the P. ovis allergens led us to characterise a glutathione S-transferase (GST) which displays homology to GST allergens isolated from the house dust mite, Dermatophagoides pteronyssinus and the cockroach, Blatella germanica. A cDNA encoding a mu-class GST from P. ovis was expressed in Escherichia coli and the recombinant protein purified for biochemical analysis. SDS-PAGE analysis indicated that the purified product was homogeneous and had an apparent molecular weight of 30 kDa. The recombinant GST (rGST) is active towards the substrate 1-chloro-2,4-dinitrobenzene (CDNB), whereas 1,2-dichloro-4-nitrobenzene (DCNB) is a poor substrate. The recombinant protein was also tested for recognition by IgE and IgG antibodies in serum from P. ovis naïve and P. ovis infested sheep. Neither IgE nor IgG antibodies were detected to the rGST. Prausnitz--Küstner testing with rGST did not provoke a characteristic weal and flare response. Biopsies collected at the PK test sites were stained for eosinophils, neutrophils, mast cells and basophils. Neutrophil, mast cell and basophil counts were not significantly different to the controls. Eosinophil numbers were significantly higher than controls, but were not due to an IgE response.

Fluorometric microplate assay to measure glutathione S-transferase activity in insects and mites using monochlorobimane

Elevated levels of glutathione S-transferases (GSTs) play a major role as a mechanism of resistance to insecticides and acaricides in resistant pest insects and mites, respectively. Such compounds are either detoxicated directly via phase I metabolism or detoxicated by phase II metabolism of metabolites as formed by microsomal monooxygenases. Here we used monochlorobimane (MCB) as an artificial substrate and glutathione to determine total GST activity in equivalents of single pest insects and spider mites in a sensitive 96-well plate-based assay system by measuring the enzymatic conversion of MCB to its fluorescent bimane-glutathione adduct. The differentiation by their GST activity between several strains of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), with different degrees of resistance to numerous acaricides was more sensitive with MCB compared to the commonly used substrate 1-chloro-2,4-dinitrobenzene (CDNB). Compared to an acaricide-susceptible reference strain, one field population of T. urticae showed a more than 10-fold higher GST activity measured with MCB, in contrast to a less than 2-fold higher activity when CDNB was used. Furthermore, we showed that GST activity can be sensitively assessed with MCB in homogenates of pest insects such as Heliothis virescens, Spodoptera frugiperda (Lepidoptera: Noctuidae), Plutella xylostella (Lepidoptera: Yponomeutidae), and Myzus persicae (Hemiptera: Aphididae).

Mechanisms of resistance to organophosphates in Tetranychus urticae (Acari: Tetranychidae) from Greece

We investigated the mechanisms conferring resistance to methyl-parathion (44-fold) and to methomyl (8-fold) in Tetranychus urticae from Greece by studying the effect of synergists on the resistance and the kinetic characteristics of various enzymes in a resistant strain (RLAB) and a susceptible reference strain (SAMB). It is shown that S,S,S-tributyl phosphorotrithioate, a synergist that inhibits esterases and glutathione S-transferases, and piperonyl butoxide, a synergist that inhibits cytochrome P450 mediated monooxygenases, did not affect the level of methyl-parathion or methomyl resistance in RLAB and that resistance ratios to both insecticides did not change significantly in the presence of either synergist. Isoelectric focusing of esterase allozymes on single mites revealed no differences in staining intensity and glutathione S-transferase activity was not significantly different in the two strains. The activity of two cytochrome P450 monooxygenase groups was compared. No significant difference of 7-ethoxyresorufin-O-diethylase activity was observed between strains that were two-fold higher in RLAB than in SAMB. The kinetic characteristics of acetylcholinesterase, the target enzyme of organophosphates and carbamates, revealed that acetylcholinesterase in RLAB was less sensitive to inhibition by paraoxon and methomyl in comparison with SAMB. I(50), the inhibitor concentration inducing 50% decrease of acetylcholinesterase activity was greater (119- and 50-fold with paraoxon and methomyl, respectively) and the bimolecular constant k(i) was lower (39- and 47-fold with paraoxon and methomyl, respectively) in RLAB compared to SAMB.

Susceptibility and detoxifying enzyme activity in two spider mite species (Acari: Tetranychidae) after selection with three insecticides

Changes in the susceptibility and detoxifying enzyme activity were measured in laboratory strains of Banks grass mite, Oligonychus pratensis (Banks), and twospotted spider mite, Tetranychus urticae Koch, that were repeatedly exposed to three insecticides. Three strains of each mite species were exposed to one of two pyrethroids, bifenthrin, and lambda-cyhalothrin, or an organophosphate, dimethoate, for 10 selection cycles at the LC60 for each insecticide. A reference or nonselected strain of each mite species was not exposed to insecticides. After 10 cycles of exposure, susceptibility to the corresponding insecticides, bifenthrin, lambda-cyhalothrin, and dimethoate, decreased 4.5-, 5.9-, and 289.2-fold, respectively, relative to the reference strain in the respective O. pratensis strains, and 14.8-, 5.7-, and 104.7-fold, respectively, relative to the reference strain in the respective T. urticae strains. In the bifenthrin-exposed O. pratensis strain, there was a 88.9-fold cross-resistance to dimethoate. In the dimethoate-exposed T. urticae strain, there was a 15.9-fold cross-resistance to bifenthrin. These results suggest that there may be cross-resistance between dimethoate and bifenthrin. The reduced susceptibility to dimethoate remained stable for three months in the absence of selection pressure in both mites. The decrease in susceptibility in the O. pratensis strains exposed to bifenthrin, lambda-cyhalothrin, and dimethoate was associated with a 4.7-, 3.0-, and 3.6-fold increase in general esterase activity, respectively. The decrease in susceptibility in the T. urticae strains exposed to bifenthrin and lambda-cyhalothrin was associated with a 1.3- and 1.1-fold increase in general esterase activity, respectively. The mean general esterase activity was significantly higher in the pyrethroid-exposed O. pratensis and T. urticae strains than in the nonselected strain. There was no significant increase in esterase activity in the dimethoate-exposed T. urticae strain. The decrease in susceptibility to insecticides was also associated with reduced glutathione S-transferase 1-chloro-2, 4-dinitrobenzene conjugation activity, but this did not appear to be related to changes in insecticide susceptibility. These results suggest that in these mites, the general esterases may play a role in conferring resistance to pyrethroids. However, some other untested mechanism, such as target site insensitivity, must be involved in conferring dimethoate resistance.

Microanatomical and microbiological characteristics of the quiescent state of Scutovertex minutus (Acari: Oribatida)

Both adults and juveniles of the oribatid mite Scutovertex minutus (Scutoverticidae) may enter an immobile quiescent state under extreme dry conditions. The microanatomy of the alimentary tract, contents of parenchyma tissue and internal extraintestinal microbial communities were observed in these states. The quiescent state lasted at least 10 days and was generally characterized by an empty gut, guanine deposition and, in adults, by the resorption of spermatids or oocytes and eggs. The homogenate of mites was sterile, without microorganisms. The reverse processes were recorded two hours after remoistening: the mites started to move again and accompanying histological changes were shown.

Detection of serine proteases in extracts of the domestic mite Blomia tropicalis

Previous studies have shown that the domestic mites Dennatophagoides pteronyssinus and D. farinae contain allergens with serine protease activity. These proteolytic allergens include trypsin, chymotrypsin, elastase, kallikrein, and C3/C5 convertase. However, it is not known whether the domestic mite Blomia tropicalis shares with other mite species the serine protease activities. The enzymatic activity present in extracts obtained from food-free B. tropicalis was investigated using specific substrates and inhibitors. Based upon the concentration response and inhibition profiles, and the digestion of specific substrates our data demonstrate that extracts from B. tropicalis exhibit several serine-protease-like activities. The enzyme activities detected in the B. tropicalis extracts are trypsin, elastase, chymotrypsin, kallikrein, C3/C5 convertase, and mast cell protease. Our results also demonstrate that kallikrein and C3/C5 convertase-like activities were not significantly affected by the alpha1-antiprotease, a naturally occurring serine protease inhibitor which protects lung mucosa from the enzymatic action. These data strongly suggest that the Echymyopodidae mite B. tropicalis shares at least five serine proteases with members of other mite families, the Glycyphagidae and Pyroglyphidae. In addition, our data demonstrate the potential use of biochemical methods to detect serine proteases for evaluation of mite growth in viitro, or to detect environmental exposures to these enzymes.

Host plant-induced changes in detoxification enzymes and susceptibility to pesticides in the twospotted spider mite (Acari: Tetranychidae)

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on lima bean plants were moved to cucumber, maize, or new lima bean plants (the latter being a control) and evaluated after 24 h or 7 d for changes in susceptibility to three pesticides and in levels of related detoxification enzymes. The largest and most consistent changes were observed in mites feeding on cucumber. Susceptibility of mites on cucumber to the synthetic pyrethroids bifenthrin and lambda-cyhalothrin was greater than that of mites reared on lima bean and maize after only 24 h on the plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to the organophosphate dimethoate than were mites on lima bean, but only after 7 d on the host. Susceptibility was inversely related to activities of both general esterase and glutathione S-transferase (GST) in mites on cucumber; general esterase and GST activities were 60 and 25% lower, respectively, than activities of twospotted spider mite on lima bean after 7 d of feeding. Mites on maize were slightly but significantly more susceptible than those on lima bean to bifenthrin, but not to lambda-cyhalothrin, after 7 d and to dimethoate after 24 h but not after 7 d. General esterase and GST activities in twospotted spider mite fed on maize for 24 h were 20 and 16% higher, respectively, than activities in twospotted spider mite on lima bean, but general esterase activity was 30% lower than lima bean-fed mites and GST was not different after 7 d. Thus, plant-induced changes in general esterase activity, perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in susceptibility of twospotted spider mite to several pesticides, particularly the synthetic pyrethroids. General esterases appear to play less of a role in the detoxification of the organophosphate insecticide dimethoate.

The transmembrane protein occludin of epithelial tight junctions is a functional target for serine peptidases from faecal pellets of Dermatophagoides pteronyssinus

There have been only a few studies of how allergens cross the airway epithelium to cause allergic sensitization. House dust mite fecal pellets (HDMFP) contain several proteolytic enzymes. Group 1 allergens are cysteine peptidases, whilst those of groups 3, 6 and 9 have catalytic sites indicative of enzymes that mechanistically behave as serine peptidases. We have previously shown that the group 1 allergen Der p 1 leads to cleavage of tight junctions (TJs), allowing allergen delivery to antigen presenting cells. In this study we determined whether HDMFP serine peptidases similarly compromise the airway epithelium by attacking TJs, desmosomes and adherens junctions. Experiments were performed in monolayers of MDCK, Calu-3 or 16HBE14o-epithelial cells. Cell junction morphology was examined by 2-photon molecular excitation microscopy and digital image analysis. Barrier function was measured as mannitol permeability. Cleavage of cell adhesion proteins was studied by immunoblotting and mass spectrometry. HDMFP serine peptidases led to a progressive cleavage of TJs and increased epithelial permeability. Desmosomal puncta became more concentrated. Cleavage of TJs involved proteolysis of the TJ proteins, occludin and ZO-1. This was associated with activation of intracellular proteolysis of ZO-1. In contrast to occludin, E-cadherin of adherens junctions was cleaved less extensively. Although Calu-3 and 16HBE14o-cells expressed tethered ligand receptors for serine peptidases, these were not responsible for transducing the changes in TJs. HDMFP serine peptidases cause cleavage of TJs. This study identifies a second general class of HDM peptidase capable of increasing epithelial permeability and thereby creating conditions that would favour transepithelial delivery of allergens.

The pest status and distribution of three cryptic blue oat mite species (Penthaleus spp.) and redlegged earth mite (Halotydeus destructor) in southeastern Australia

Earth mites are pests of crops and pastures in southeastern Australia. Recent studies show differences between earth mite species in their mode of reproduction, preferred hosts and pesticide tolerance. This paper examines the distribution and pest status of each species. The southeastern Australian distribution for each species is mapped, incorporating new data from eastern New South Wales, South Australia and Tasmania. A new population of an undescribed species previously identified from northwestern Victoria was found in northern New South Wales. CLIMEX was used to identify climatic factors limiting the distribution of P. major and P. falcatus, the most broadly distributed species. This analysis suggests tolerance to heat and desiccation limits the inland distribution of these two species. A three-year survey of agricultural outbreaks indicates that all Penthaleus species are major agricultural pests although their pest status on crop types appears to differ. All species contributed to chemical control failures. However P. falcatus, previously identified in laboratory tests as having increased tolerance to pesticides, was the most common species associated with control failures. A laboratory experiment indicated that mites are sometimes pests on crops on which they cannot persist for a generation. Results are discussed with respect to management of these agricultural pests.

Presence of chitinase in adult Varroa destructor, an ectoparasitic mite of Apis mellifera

The enzyme spectrum of an ectoparasitic mite of the honeybee. Varroa destructor (Anderson and Trueman) was studied using a semi-quantitative method, especially designed for complex samples which have not been purified. Exopeptidases and phosphatases are shown present. A chitinase and enzymes able to transform beta carbohydrates are also present with a large range in the intensity of the reaction. The role of the chitinase can be related to the supply of nutritional needs or/and the piercing and sucking behaviour of the adult parasite. Chitinase activity could be one factor influencing the balance between the parasite and its host.

Oncostatin M synergises with house dust mite proteases to induce the production of PGE(2) from cultured lung epithelial cells

The release of PGE(2) and nitric oxide (NO) from the respiratory epithelium may act to dampen inflammation. In other tissues, oncostatin M (OSM), a potent inducer of epithelial antiproteases, has also been shown to interact with IL-1beta to stimulate PGE(2) release. However, whether OSM interacts with pro-inflammatory cytokines and proteases in the production of anti-inflammatory eicosanoids and NO from airway epithelium is unknown. The effect of OSM and the related cytokine leukaemia inhibitory factor (LIF) on PGE(2) and NO production by the respiratory epithelial cell line, A549 in response to pro-inflammatory cytokines as well as protease-rich house dust mite (HDM) fractions and a protease-deficient rye grass pollen extract was examined by immunohistochemistry, cell culture, ELISA and enzyme-immunoassay. Cells treated with a mixture of IL-1beta, IFNgamma and LPS for 48 h produced a 9 fold increase in PGE(2) and a 3 fold increase in NO levels (both P<0.05). Both OSM and LIF were without effect. However, OSM added together with the cytokine mixture synergistically enhanced PGE(2) production (22 fold, P<0.05). OSM also synergistically enhanced PGE(2) production in response to a cysteine protease-enriched, but not serine protease-enriched HDM fraction (P<0.05). Rye grass extract, neither alone nor in combination with OSM, induced PGE(2) or NO production, although it did induce the release of GM-CSF. These observations suggest that OSM is an important co-factor in the release of PGE(2) and NO from respiratory epithelial cells and may play a role in defense against exogenous proteases such as those derived from HDM.

Genetic differences among host-associated populations of water mites (Acari: Unionicolidae: Unionicola): allozyme variation supports morphological differentiation

Unionicola poundsi and U. lasallei are recognized as closely related, morphologically distinct species of water mites living in symbiotic association with the mussels Villosa villosa and Uniomerus declivus, respectively. However, results of a transplant experiment suggested that the morphological characters used to separate these species are plastic and are influenced by the host species in which these mites metamorphose. These results indicate that U. poundsi and U. lasallei are variants of the same species. To test the validity of these contrasting notions, the genetic structure of mite populations from Uniomerus declivus and V. villosa was compared. An examination of allozyme variation at 9 enzyme loci revealed a high degree of genetic differentiation between these host-associated populations, with mites from U. declivus and V. villosa being fixed for different alleles at 3 loci and exhibiting significant allele heterogeneity at 71% of their polymorphic loci. Coefficients of genetic similarity and genetic distance for mites from U. declivus and V. villosa were 0.36 and 0.95, respectively. The results of this study suggest that mite populations from U. declivus and V. villosa are genetically distinct and complement morphological data recognizing them as valid species.

Biochemical and immunological characterization of a recombinant precursor form of the house dust mite allergen Der p 1 produced by Drosophila cells

BACKGROUND

The major house dust mite allergen Der p 1 elicits strong IgE antibody responses in patients suffering from mite allergy.

OBJECTIVE

This study reports the expression and characterization of a recombinant precursor form of Der p 1 secreted as ProDer p 1 from insect cells.

METHODS

The cDNA coding for ProDer p 1 was cloned downstream to the gp67 signal peptide, starting from commercial cDNA encoding Der p 1 and PCR-amplified ProDer p 1 genomic fragment. ProDer p 1, expressed in Drosophila cells and purified from culture medium, was compared to Der p 1 isolated from mite culture, in terms of glycosylation, enzymatic activity as well as IgG- and IgE-binding capacity.

RESULTS

Sequence analysis of the genomic clone of ProDer p 1 revealed that, besides two introns in the mature Der p 1 coding sequence, two introns were also present in the propeptide coding sequence. ProDer p 1 was purifed to homogeneity by a combination of ion-exchange, hydroxyapatite and gel filtration chromatographies. The precursor form of Der p 1 could be processed in vitro into mature Der p 1 under acidic and reducing conditions. Carbohydrate analysis clearly indicated that ProDer p 1 expressed from insect cells was glycosylated and that glycan structures were located only in the prosequence. ProDer p 1 displayed a similar immunoreactivity towards IgE, monoclonal and polyclonal IgG antibodies compared to natural Der p 1. Specific activity measurements using synthetic substrates clearly indicated that, contrary to natural Der p 1, ProDer p 1 was totally enzymatically inactive.

CONCLUSIONS

The expression of an enzymatically inactive and highly antigenic ProDer p 1 zymogen molecule could be a suitable strategy for the development of in vitro diagnosis test as well as for specific immunotherapy.

Characterization of proteases from a stored product mite, Tyrophagus putrescentiae

Extracts of Tyrophagus putrescentiae feces exhibited higher (>50-fold) specific protease activity rates than those measured using mite body extracts for the substrates azocasein, BApNa, SA(2)PPpNa, HA, and HPA. This suggests that trypsin, chymotrypsin, and carboxypeptidases A and B are involved in mite digestion. Hydrolysis of the substrates ZAA(2)MNA and LpNa was only 3 times higher in fecal extracts, suggesting that levels of cathepsin B and aminopeptidases in the lumen of the digestive tract are low compared to the other enzymes. The hydrolysis of hemoglobin was only detected in body extracts indicating that cathepsin D is not a digestive protease in this species. Protease inhibitors of different specificity were tested invivo to establish their potential as control agents. We found that development from larvae to adult was significantly retarded in larvae fed on brewers' yeast containing inhibitors of serine proteases, whereas no such effect was found with inhibitors of cysteine and aspartyl proteases. Interestingly, when dietary mixtures of serine protease, aminopeptidase and carboxypeptidase inhibitors were fed to T.putrescentiae, a synergistic effect was observed that retarded development. Several plant lectins were also tested, but none affected development.

First detection in Israel of fluvalinate resistance in the varroa mite using bioassay and biochemical methods

The aim of this study was to explore the extent of varroa mite resistance to fluvalinate in Israel and to determine the underlying biochemical mechanism. Assays at different apiaries indicated varroa mite resistance at three of the five sites tested. Dose response assays conducted with tau-fluvalinate on mites obtained from different sites indicated uneven resistance. A monooxygenase assay revealed an increased rate (approximately 20-fold) of activity in mites that were not controlled by the pesticide, as compared to activity in mites from untreated colonies. A minor, 1.5-2.5 fold, increase of esterase activity was also noted in the resistant mites. This first demonstration of a fluvalinate-resistance mechanism in varroa mites points to the need for more vigorous resistance management practices to control the pest.

A comparative survey of the hydrolytic enzymes of ectoparasitic and free-living mites

Extracts of ectoparasitic mites of birds (Dermanyssus gallinae), sheep (Psoroptes ovis) and plants (Tetranychus urticae) and of free-living mites (Acarus siro) contained acid and alkaline phosphatase, C4 and C8 esterases, lipase, leucine and valine aminopeptidases and a range of glycosidase activities. Dermanyssus gallinae and P. ovis, species highly adapted to an animal parasitic lifestyle, had very similar profiles and contained low activities of glycosidases. In contrast, the polyphagous species A. siro contained moderate to high activities of every glycosidase examined, whereas the phytophagous species, T. urticae, displayed high activities of only beta-galactosidase and beta-glucuronidase. All extracts hydrolysed haemoglobin with optima below pH6, and this hydrolysis was associated with an aspartic proteinase and variable cysteine proteinase activity dependent on species. Inhibitor-labelling with biotinyl-Phe-Ala-FMK revealed the presence of cysteine proteinases with molecular masses of 25-33.5kDa. Each mite species contains the enzymes necessary to complete digestion of the diet in the intracellular lysosomal compartment. The absolute and relative activities of each enzyme varied, and are discussed according to phylogeny and dietary habit.

Interspecific diversity of mitochondrial COI sequences in Japanese Panonychus species (Acari: Tetranychidae)

Sequences of a part of the mitochondrial cytochrome oxidase subunit I (COI) gene were analyzed in four Japanese Panonychus species to determine their phylogenetic relationships. Neighbor-Joining and maximum likelihood analysis resulted in a high bootstrap support of the relationships within the genus Panonychus. In contrast with a previous study based on ribosomal DNA data, the COI phylogeny suggested that P. mori was more distantly related to P. citri than to P. ulmi. This study shows for the first time that P. osmanthi is closely related to P. citri. Intraspecific variation analysis shows that the genetic distance between two local populations of P. mori is higher than between P. citri and P. osmanthi.

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.

Inhibition of Df-protease associated with allergic diseases by polyphenol

It was reported that Df-protease from house dust mite (Dermatophagoides farinae) catalyzes the activation of the kallikrein-kinin system in human plasma and is closely associated with mite-induced allergy. Therefore, to prevent the release of kinin by Df-protease, the inhibitory activity of polyphenols including catechins and flavonols was tested in vitro and in vivo. Among them, myricetin and epigallocatechin gallate (EGCg) effectively inhibited the amidase activity of Df-protease with K(i) values of 1 x 10(-)(8) and 6 x 10(-)(4) M, respectively. The kinin release in human plasma was extensively inhibited by the addition of EGCg in comparison with myricetin. Enhancement of vascular permeability in guinea pigs caused by Df-protease was markedly suppressed by EGCg.