Predatory Mite Metaseiulus Occidentalis Research Articles

Significant transcriptional changes in mature daughter Varroa destructor mites during infestation of different developmental stages of honeybees.

Varroa destructor is considered a major cause of honeybee (Apis mellifera) colony losses worldwide. Although V. destructor mites exhibit preference behavior for certain honeybee lifecycle stages, the mechanism underlying host finding and preference remains largely unknown. By using a de novo transcriptome assembly strategy, we sequenced the mature daughter V. destructor mite transcriptome during infestation of different stages of honeybees (brood cells, newly emerged bees and adult bees). A total of 132 779 unigenes were obtained with an average length of 2745 bp and N50 of 5706 bp. About 63.1% of the transcriptome could be annotated based on sequence homology to the predatory mite Metaseiulus occidentalis proteins. Expression analysis revealed that mature daughter mites had distinct transcriptome profiles after infestation of different honeybee stages, and that the majority of the differentially expressed genes (DEGs) of mite infesting adult honeybees were down-regulated compared to that infesting the sealed brood cells. Gene ontology and KEGG pathway enrichment analyses showed that a large number of DEGs were involved in cellular process and metabolic process, suggesting that Varroa mites undergo metabolic adjustment to accommodate the cellular, molecular and/or immune response of the honeybees. Interestingly, in adult honeybees, some mite DEGs involved in neurotransmitter biosynthesis and transport were identified and their levels of expression were validated by quantitative polymerase chain reaction (qPCR). These results provide evidence for transcriptional reprogramming in mature daughter Varroa mites during infestation of honeybees, which may be relevant to understanding the mechanism underpinning adaptation and preference behavior of these mites for honeybees. © 2020 Society of Chemical Industry.

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.

Cloning and Functional Characterization of Two BTB Genes in the Predatory Mite Metaseiulus occidentalis.

Proteins containing the BTB (Bric-à-brac, tramtrack, and Broad Complex) domain typically share low sequence similarities and are involved in a wide range of cellular functions. We previously identified two putative and closely related BTB genes, BTB1 and BTB2, in the genome of the predatory mite Metaseiulus occidentalis. In the current study, full-length BTB1 and BTB2 cDNAs were cloned and sequenced. BTB1 and BTB2 encode proteins of 380 and 401 amino acids, respectively. BTB1 and BTB2 proteins each contain an N-terminal BTB domain and no other identifiable domains. Thus, they belong to a large category of BTB-domain proteins that are widely distributed in eukaryotes, yet with largely unknown function(s). BTB1 and BTB2 gene knockdowns in M. occidentalis females using RNAi reduced their fecundity by approximately 40% and 73%, respectively, whereas knockdown had no impact on their survival or the development of their offspring. These findings suggest these two proteins may be involved in processes related to egg production in this predatory mite, expanding the list of functions attributed to these diverse proteins.

A single nucleotide polymorphism in the acetylcholinesterase gene of the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae) is associated with chlorpyrifos resistance

The predatory mite Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) is one of the most important biocontrol agents of herbivorous mites in European perennial crops. The use of pesticides, such as organophosphate insecticides (OPs), is a major threat to the success of biocontrol strategies based on predatory mites in these cropping systems. However, resistance to OPs in K. aberrans has recently been reported. The present study investigated the target site resistance mechanisms that are potentially involved in OP insensitivity. In the herbivorous mite Tetranychus urticae Koch (Acari: Tetranychidae), resistance to OPs is due to a modified and insensitive acetylcholinesterase (AChE; EC: 3.1.1.7) that bears amino acid substitution F331W (AChE Torpedo numbering). To determine whether the predators and prey have evolved analogous molecular mechanisms to withstand the same selective pressure, the AChE cDNA from a putative orthologous gene was cloned and sequenced from susceptible and resistant strains of K. aberrans. No synonymous mutation coding for a G119S substitution was determined to be strongly associated with the resistant phenotype instead of the alternative F331W. Because the same mutation in T. urticae AChE was not associated with comparable levels of chlorpyrifos resistance, the role of the G119S substitution in defining insensitive AChE in K. aberrans remains unclear. G119S AChE genotyping can be useful in ecological studies that trace the fate of resistant strains after field release or in marker-assisted selection of improved populations of K. aberrans to achieve multiple resistance phenotypes through gene pyramiding. The latent complexity of the target site resistance in K. aberrans vs. that of T. urticae is also discussed in the context of data from the genome project of the predatory mite Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae).

Expression analysis of Drosophila doublesex, transformer-2, intersex, fruitless-like, and vitellogenin homologs in the parahaploid predator Metaseiulus occidentalis (Chelicerata: Acari: Phytoseiidae).

Characterization and expression analyses are essential to gain insight into sex-determination pathways in members of the Acari. Little is known about sex determination at the molecular level in the western orchard predatory mite Metaseiulus occidentalis (Arthropoda: Chelicerata: Arachnida: Acari: Phytoseiidae), a parahaploid species. In this study, eight genes previously identified as putative homologs to genes involved in the sex-determination pathway in Drosophila melanogaster were evaluated for sex-specific alternative splicing and sex-biased expression using reverse-transcriptase PCR and quantitative real-time PCR techniques, respectively. The homologs evaluated in M. occidentalis included two doublesex-like genes (Moccdsx1 and Moccdsx2), transformer-2 (Mocctra-2), intersex (Moccix), two fruitless-like genes (MoccBTB1 and MoccBTB2), as well as two vitellogenin-like genes (Moccvg1 and Moccvg2). Single transcripts of equal size were detected in males and females for Moccdsx1, Moccdsx2, Mocctra-2, Moccix, and MoccBTB2, suggesting that their pre-mRNAs do not undergo alternative splicing in a sex-specific manner. Three genes, Moccdsx1, Moccdsx2 and MoccBTB2, displayed male-biased expression relative to females. One gene, Moccix, displayed female-biased expression relative to males. Two genes, Mocctra-2 and MoccBTB1, did not display detectable differences in transcript abundance in males and females. Expression of Moccvg1 and Moccvg2 were detected in females only, and transcript levels were up-regulated in mated females relative to unmated females. To our knowledge, this represents the first attempt to elucidate expression patterns of putative sex-determination genes in an acarine. This study is an initial step towards understanding the sex-determination pathway in the parahaploid M. occidentalis.

Clathrin heavy chain is important for viability, oviposition, embryogenesis and, possibly, systemic RNAi response in the predatory mite Metaseiulus occidentalis.

Clathrin heavy chain has been shown to be important for viability, embryogenesis, and RNA interference (RNAi) in arthropods such as Drosophila melanogaster. However, the functional roles of clathrin heavy chain in chelicerate arthropods, such as the predatory mite Metaseiulus occidentalis, remain unknown. We previously showed that dsRNA ingestion, followed by feeding on spider mites, induced systemic and robust RNAi in M. occidentalis females. In the current study, we performed a loss-of-function analysis of the clathrin heavy chain gene in M. occidentalis using RNAi. We showed that ingestion of clathrin heavy chain dsRNA by M. occidentalis females resulted in gene knockdown and reduced longevity. In addition, clathrin heavy chain dsRNA treatment almost completely abolished oviposition by M. occidentalis females and the few eggs produced did not hatch. Finally, we demonstrated that clathrin heavy chain gene knockdown in M. occidentalis females significantly reduced a subsequent RNAi response induced by ingestion of cathepsin L dsRNA. The last finding suggests that clathrin heavy chain may be involved in systemic RNAi responses mediated by orally delivered dsRNAs in M. occidentalis.

Molecular characterization and evolutionary insights into potential sex-determination genes in the western orchard predatory mite Metaseiulus occidentalis (Chelicerata: Arachnida: Acari: Phytoseiidae)

Little is known about the process of sex determination at the molecular level in species belonging to the subclass Acari, a taxon of arachnids that contains mites and ticks. The recent sequencing of the transcriptome and genome of the western orchard predatory mite Metaseiulus occidentalis allows investigation of molecular mechanisms underlying the biological processes of sex determination in this predator of phytophagous pest mites. We identified four doublesex-and-mab-3-related transcription factor (dmrt) genes, one transformer-2 gene, one intersex gene, and two fruitless-like genes in M. occidentalis. Phylogenetic analyses were conducted to infer the molecular relationships to sequences from species of arthropods, including insects, crustaceans, acarines, and a centipede, using available genomic data. Comparative analyses revealed high sequence identity within functional domains and confirmed that the architecture for certain sex-determination genes is conserved in arthropods. This study provides a framework for identifying potential target genes that could be implicated in the process of sex determination in M. occidentalis and provides insight into the conservation and change of the molecular components of sex determination in arthropods.

Shared Gene Structures and Clusters of Mutually Exclusive Spliced Exons within the Metazoan Muscle Myosin Heavy Chain Genes

Multicellular animals possess two to three different types of muscle tissues. Striated muscles have considerable ultrastructural similarity and contain a core set of proteins including the muscle myosin heavy chain (Mhc) protein. The ATPase activity of this myosin motor protein largely dictates muscle performance at the molecular level. Two different solutions to adjusting myosin properties to different muscle subtypes have been identified so far: Vertebrates and nematodes contain many independent differentially expressed Mhc genes while arthropods have single Mhc genes with clusters of mutually exclusive spliced exons (MXEs). The availability of hundreds of metazoan genomes now allowed us to study whether the ancient bilateria already contained MXEs, how MXE complexity subsequently evolved, and whether additional scenarios to control contractile properties in different muscles could be proposed, By reconstructing the Mhc genes from 116 metazoans we showed that all intron positions within the motor domain coding regions are conserved in all bilateria analysed. The last common ancestor of the bilateria already contained a cluster of MXEs coding for part of the loop-2 actin-binding sequence. Subsequently the protostomes and later the arthropods gained many further clusters while MXEs got completely lost independently in several branches (vertebrates and nematodes) and species (for example the annelid Helobdella robusta and the salmon louse Lepeophtheirus salmonis). Several bilateria have been found to encode multiple Mhc genes that might all or in part contain clusters of MXEs. Notable examples are a cluster of six tandemly arrayed Mhc genes, of which two contain MXEs, in the owl limpet Lottia gigantea and four Mhc genes with three encoding MXEs in the predatory mite Metaseiulus occidentalis. Our analysis showed that similar solutions to provide different myosin isoforms (multiple genes or clusters of MXEs or both) have independently been developed several times within bilaterian evolution.

Physiology of invertebrate oxytocin and vasopressin neuropeptides

New findings• What is the topic of this review?This article describes the discovery and function of invertebrate oxytocin and vasopressin neuropeptides.• What advances does it highlight?The novel discovery of oxytocin-like peptides in arthropods is described. An up-to date overview is gven of the functional role (physiology and behaviour) of oxytocin and vasopressin signalling. The application of natural peptides for drug development is discussed.Neuropeptides and regulatory peptide hormones control many developmental, physiological and behavioural processes in animals, including humans. The nonapeptides oxytocin and arginine vasopressin are produced and released by the pituitary gland and have actions on many organs and tissues. Receptive cells possess particular receptors to which the peptides bind as ligands, leading to activation of G-protein-coupled receptors, hence cellular responses. In humans and other mammalian species, oxytocin and vasopressin mediate a range of peripheral and central physiological functions that are important for osmoregulation, reproduction, complex social behaviours, memory and learning. The origin of the oxytocin/vasopressin signalling system is thought to date back more than 600 million years. All vertebrate oxytocin- and vasopressin-like peptides have presumably evolved from the ancestral nonapeptide vasotocin by gene duplication and today are present in vertebrates, including mammals, birds, reptiles, amphibians and fish. Oxytocin- and vasopressin-like peptides have been identified in several invertebrate species, including molluscs, annelids, nematodes and arthropods. Members of this peptide family share high sequence similarity, and it is possible that they are functionally related across the entire animal kingdom. However, it is evident that not all animals express oxytocin/vasopressin neuropeptides and that there is little information available about the biology and physiology of this signalling system of invertebrates and, in particular, of insects, which represent more than half of all known living organisms. This report describes the discovery of novel oxytocin- and vasopressin-like peptides in arthropods and summarizes the status quo of the functional relevance of this neuropeptide signalling system in invertebrates, which will have beneficial implications for the design of selective and potent ligands to human oxytocin and vasopressin receptors.

Evaluation of proxies for quality of Metaseiulus occidentalis (Acari: Phytoseiidae) reared on different stages of Tetranychus urticae (Acari: Tetranychidae)

Experiments were conducted to determine if two different methods for assessing quality of the predatory mite Metaseiulus (=Galendromus or Typhlodromus) occidentalis (Nesbitt) (Acari: Phytoseiidae) could be used instead of the more-lengthy and tedious life-history assessment method. First, an experiment was conducted to confirm it was possible to develop females of confirmed different quality by rearing immatures on two diets (eggs only or actives only of Tetranychus urticae Koch (Acari: Tetranychidae). Metaseiulus occidentalis females had a higher total fecundity (15.6 vs. 8.5 eggs female−1), a higher daily fecundity (2.2 vs. 1.4 eggs female−1 day−1), a higher survival rate (100% vs. 56.7%) over 7days of evaluation, and a higher rate of developmental success of their progeny (96.4% vs. 69.5%) when fed eggs only rather than actives only, respectively. The results confirmed adult females of known different quality could be produced for evaluating potential quality-control assessment methods. Two potential quality-control metrics were investigated using these females: survival time of females when held without food and water, and size (length and width) of their dorsal shields. Starvation time and body size were influenced significantly by both diet type and mating status, but the differences obtained were insufficient to use as proxies for evaluating the quality of the M. occidentalis females of known different quality.

Transcriptome sequencing and annotation of the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae): a cautionary tale about possible contamination by prey sequences

Next-generation sequencing was applied to the transcriptome of the phytoseiid Metaseiulus occidentalis to characterize gene expression in all life stages reared under different conditions to optimize the recovery of as many genes as possible. One production and one titration run produced a total of 862,069 reads (average size: 314.87 bp), which generated 255.6 Mbp of sequences on the GS-FLX Titanium sequencing platform. After removal of putative prey sequences 850,543 reads were used in NewBler and PTA assemblies to produce 74,172 non-redundant sequences, including 30,691 contigs and 43,481 singlets with 11,994 contigs consisting of more than 500 bp and 37,278 sequences >300 bp, constituting 48.7 % of all sequences. There were 25,888 hits with the NCBI non-redundant database and 15,376 unique transcripts. There were 26,225 hits with the Ixodes scapularis genome and 6,634 unique transcripts. There were 22,225 hits with the RefSeq of Homo sapiens with 6,465 unique transcripts, and 23,656 hits with the RefSeq of Drosophila melanogaster with 9,216 unique transcripts. Selected ESTs corresponding to genes of interest were analyzed including those related to transposable elements, GPCRs, Sox transcription factors, diapause and foraging behavior, and pesticide resistances. Novel and important genes appear to have been discovered that provide insight into the evolution, biology, and physiology of this important predator of pest mites in agriculture and will be useful in analyzing complete genome sequences of this natural enemy.

Cardinium is associated with reproductive incompatibility in the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae)

Cardinium, a bacterium from the Bacteroidetes group, is associated with reproductive manipulations such as cytoplasmic incompatibility, parthenogenesis, and feminization in some arthropod species. We, and others, have shown that Cardinium, but not Wolbachia, is an endosymbiont in some populations of Metaseiulus occidentalis, a phytoseiid mite that is an important predator of spider mite pests of agricultural crops. However, the precise biological effects that Cardinium may have on M. occidentalis remain unclear. In this study we show, in two sets of crosses between different colonies of Cardinium-free (C−) M. occidentalis females and Cardinium-containing (C+) males, that fecundity was reduced in parental females, F1 progeny survival rates were reduced, and fewer female progeny were produced when compared to the reciprocal and control crosses. There were no differences in these attributes in the reciprocal and two control crosses. Cardinium was transmitted maternally but there was no observed paternal transmission. Finally, Cardinium did not cause asexual (thelytoky) reproduction in M. occidentalis. Thus, Cardinium is associated with nonreciprocal reproductive incompatibility in M. occidentalis and our results support the hypothesis that Cardinium is a reproductive parasite in this agriculturally important predator. Cardinium may therefore affect the evolution and ecology of M. occidentalis and biological control efforts using this mite.

Extended starvation reduced and eliminated Wolbachia, but not Cardinium, from Metaseiulus occidentalis females (Acari: Phytoseiidae): A need to reassess Wolbachia’s status in this predatory mite?

The presence of Wolbachia and Cardinium bacteria has been documented in many arthropod species, including the predatory mite Metaseiulus (=Typhlodromus or Galendomus) occidentalis (Nesbitt) (Acari: Phytoseiidae). We show that Tetranychus urticae, the prey of Metaseiulus occidentalis, contains Wolbachia and no detectable Cardinium using quantitative PCR (qPCR). Starvation for 72h at 22°C eliminated most, if not all, Wolbachia in M. occidentalis adult females from 7 laboratory colonies. Refeeding of M. occidentalis with T. urticae after starvation for 72h restored the amounts of Wolbachia in M. occidentalis to those of prestarvation levels, suggesting that Wolbachia detected in M. occidentalis starved for shorter periods of time in current, and some previous, studies likely came from T. urticae. Furthermore, eggs from all M. occidentalis colonies examined were free of Wolbachia if they were surface-decontaminated with 0.3% sodium hypochlorite before DNA extraction. Cardinium was present in 6 of 14 laboratory colonies of M. occidentalis. Starvation for 3, 24, 48, and 72h had no effect on the amounts of Cardinium in adult females from the Cardinium-positive colonies. Eggs from these colonies were positive for Cardinium but contained less than 1% of the titers found in adult females. The data suggest that Cardinium, but not Wolbachia, is an endosymbiont in certain populations of M. occidentalis. In light of our current findings, we recommend specific practices for the identification of potential symbionts in predatory arthropod species using the PCR.

Symbionts, including pathogens, of the predatory mite Metaseiulus occidentalis: current and future analysis methods

Metaseiulus (= Typhlodromus or Galendromus) occidentalis (Nesbitt) (Acari: Phytoseiidae) is an effective natural enemy of pest mites in a variety of crops around the world, although it is considered to be endemic in the western USA. A broad understanding of much of its biology, ecology, behavior, and genetics has been obtained over the past 60 years, but the role(s) symbionts play, which includes pathogens and other microorganisms, remains to be resolved fully. Until molecular tools became available, analysis methods were limited primarily to microscopic observations; some viruses and rickettsia-like organisms were observed infecting 'diseased' M. occidentalis, but it is not clear which one(s) was the causal agent(s) of the disease(s). Subsequent to the development of the polymerase chain reaction (PCR) and genome sequencing, we identified putative gut symbionts and reproductive tract symbionts in M. occidentalis, as well as a microsporidian pathogen. A new phylogenetic analysis of the Bacteroidetes-Flavobacterium group suggests the unnamed Bacteroidetes in M. occidentalis is associated with the digestive tract. However, much of our current information about the role these microorganisms play in the biology of M. occidentalis is based on correlation, lacking the strength of fulfilling Koch's postulates. We also currently lack any knowledge of the importance of these microorganisms under field conditions. In the future, it should be possible to learn what role(s) these organisms play in the biology of this important predator using metagenomics approaches to analyze the transcriptome and to determine their relative abundance within their hosts with the quantitative PCR. We have just begun to resolve these relationships.

The mitochondrial genome of the predatory mite Metaseiulus occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) is unexpectedly large and contains several novel features

The complete mitochondrial genome of the phytoseiid Metaseiulus occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) has been sequenced. It is 24,961 bp in length and contains a 14,695-bp unique region, a 345-bp triplicated region, and a 9921-bp duplicated region, in that order. The A+T content of the unique region is 76.9% and contains 11 protein coding ( COI–III; ATP6–8; CytB; ND1, 2, 4, 5 and 4L), two ribosomal RNA ( srRNA and lrRNA), 22 transfer RNA ( tRNA) genes, and two copies of D-loop control sequence. Two genes ( ND3 and 6) appear to be missing, but there is a large intergenic spacer (390 bp) present, which could contain ND3 if a different codon usage is employed. The gene order is completely different from the pattern in all other known chelicerates, including the horseshoe crab Limulus polyphemus [Lavrov et al., Mol. Biol. Evol., 2000; 17:813–824]. All the inferred tRNA genes are missing the TΨC arm, but this arm has fused with the variable arm to generate a TV replacement loop. The duplicated region (9921 bp) contains 18 genes in the same order as in the unique region from CytB to tRNA-His, plus one copy of D-loop control sequence (311 bp) and a partial tRNA-Leu2 sequence (34 bp). The small triplicated region (345 bp) contains a D-loop control sequence (311 bp) and a partial tRNA-Leu2 sequence (34 bp). Because of these anomalies, amplifying sequences posed technical difficulties, but were accomplished by using a primer-walking strategy and increasing the AT content to 75% in the high-fidelity PCR dNTP mix. This is the first phytoseiid mitochondrial genome to be completely sequenced and the largest (25 kb) detected from the Chelicerata.

Microbial diversity in the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae) and its prey, Tetranychus urticae (Acari: Tetranychidae)

Abstract Microorganisms associated with the predatory mite Metaseiulus (= Typhlodromus or Galendromus ) occidentalis (Nesbitt) and its prey, the two-spotted spider mite Tetranychus urticae (Koch), were assessed using a high-fidelity polymerase chain reaction (PCR) protocol and primers designed to identify Eubacteria, Archaeabacteria, iridoviruses, Helicosporidia, Cytophaga -like microorganisms, Wolbachia and its bacteriophage WO, fungi and yeast-like organisms. Sequences from four bacterial species related to Wolbachia (α-Proteobacteria), Cardinium , Bacteroidetes , and Enterobacter (γ-Proteobacteria) were obtained from M. occidentalis , and three sequences related to Wolbachia , Rickettsia , and Caulobacter (α-Proteobacteria) were obtained from T. urticae . No nucleotide differences were detected between the 16S rRNA, wspA or wspB Wolbachia sequences obtained from M. occidentalis and T. urticae , which suggest that horizontal transfer of Wolbachia could have occurred. Southern blot analyses of genomic DNA from both M. occidentalis and T. urticae using wspA probes were negative, indicating that this Wolbachia sequence is not integrated into the nuclear genome of either species. Two of the T. urticae colonies tested contained the WO bacteriophage, but none of the six M. occidentalis populations were infected. New M. occidentalis -specific forward and reverse 16S rRNA primers based on the Wolbachia , Cardinium , Bacteroidetes , and Enterobacter sequences obtained were designed and used to amplify PCR products from each of two laboratory and four field-collected samples of M. occidentalis females and eggs, indicating that these infections are widespread. Likewise, species-specific primers for T. urticae were designed for the Wolbachia , Rickettsia , and Caulobacter sequences obtained and used to evaluate T. urticae from strawberries, wine grapes, hops, almonds, and cherries from California, Washington, and Florida; all were positive for Wolbachia and Caulobacter but two of the six were negative for Rickettsia . None of the M. occidentalis colonies tested were positive for the microsporidium Oligosporidium occidentalis , which previously had been associated with a pathogenic condition in some of our laboratory colonies. The Gainesville colonies of M. occidentalis and T. urticae were negative for iridovirus, Archaeabacteria, fungi, Helicosporidia, and yeast-like organisms. So far, Wolbachia is the only symbiont that is shared by this predator and its prey.

Morphological and molecular characterization of a new microsporidian species from the predatory mite Metaseiulus occidentalis (Nesbitt) (Acari, Phytoseiidae).

A new microsporidian species is described from the predatory mite Metaseiulus (formerly Typhlodromus or Galendromus) occidentalis (Nesbitt) (Acari, Phytoseiidae). The ultrastructure of this new species is presented together with the first molecular characterization for a microsporidium of mites. All stages of this new microsporidium are haplokaryotic and develop in direct contact with the host-cell cytoplasm. Sporogony is disporoblastic and spores are formed in eggs, immature stages, and adults of M. occidentalis. There are two morphological classes of spores, one with a short polar filament (3-5 coils) that measured 2.53 x 1.68 microm and one with a longer polar filament (8-9 coils) that measured 3.14 x 1.77 microm. Horizontal transmission of this new species occurs by cannibalism of eggs and other stages and perhaps involves the spores with the long polar filament. Spores with the short polar filament may play a role in autoinfection and vertical (transovarial) transmission that is highly efficient in transferring the microsporidium from adults to progeny. Analysis of the small subunit ribosomal DNA indicated that this species from M. occidentalis is most closely related to the Nosema/Vairimorpha clade of microsporidia. A conflict between the morphological and molecular data is discussed. The species is compared to previously described microsporidia of arachnids resulting in creation of Oligosporidium occidentalis n. sp. in the family Unikaryonidae.

Heat curing Metaseiulus occidentalis (Nesbitt) (Acari, Phytoseiidae) of a fitness-reducing microsporidium.

Laboratory colonies of the predatory mite Metaseiulus occidentalis in Gainesville, FL were found to be infected with an undescribed microsporidium. Experiments were performed to quantify the effect of infection on the fitness of M. occidentalis and to determine if heat treatment can cure mites of the microsporidium. The colonies tested were derived from an isofemale line so that differences in performance could be attributed to the presence of microsporidia. A subcolony of an uninfected isofemale line was infected with the microsporidium by feeding females infected eggs from another colony of M. occidentalis. Infected mites had a shorter mean (+/-SD) female life span (7.4 +/- 2.9 vs. 10.0 +/- 2.8 days), lower mean oviposition (1.6 +/- 0.7 vs. 2.2 +/- 0.4 eggs/day), and a male-biased sex ratio (43 +/- 16% vs. 57 +/- 15% female progeny). The infection was reduced temporarily in colonies initiated from mites that were reared in a growth chamber at 33 degrees C from egg to adult, but healthy colonies only were established from the progeny of the heat-treated adults. These colonies remained free of infection for 10 weeks.

Effects of Predation and Competition on the Population Dynamics of Tetranychus pacificus on Grapevines

The Pacific spider mite Tetranychus pacificus and the Willamette spider mite Eotetranychus willamettei are herbivore pests of grapevines in California. The two spider mite species share a common and often effective phytoseiid predator, the Western orchard predatory mite Metaseiulus occidentalis. It has been suggested that E. willamettei may be beneficial in vineyards because it may have a negative impact on the more damaging T. pacificus through their shared predator or through some form of interspecific competition. We conducted field and greenhouse experiments to determine the relative effects of these interactions between the two herbivores on the population dynamics of T. pacificus in 'Thompson Seedless' grape vineyards. We also used the field data to generate a functional relationship for the combined impact of E. willamettei and M. occidentalis on T. pacificus. Predation and predator-mediated apparent competition were the only factors affecting T. pacificus densities in the field experiment. The addition of the predatory mite M. occidentalis alone resulted in a significant reduction in T. pacificus densities, while the addition of E. willamettei alone had little impact on T. pacificus densities. The greatest reductions in T. pacificus densities occurred in plots where both the predatory mite M. occidentalis and E. willamettei were added. The predatory mite occurred earliest and increased at the greatest rate in plots where it was released along with E. willamettei. From April to June, M. occidentalis abundance was positively correlated with E. willamettei abundance while T. pacificus abundance in July and August was negatively correlated with M. occidentalis abundance in the period April to June. Under greenhouse conditions, the addition of E. willamettei to T. pacificus vines resulted in a marked decrease in T. pacificus population growth rate. In contrast, doubling T. pacificus abundance in the absence E. willamettei did not affect T. pacificus population growth rate, indicating that interspecific competition is more important than intraspecific competition in determining T. pacificus abundance. Contrary to the greenhouse data and other studies in 'Zinfandel' vineyards, we found no evidence that E. willamettei competed with T. pacificus in the absence of predation in a Thompson Seedless vineyard. We suggest that the outcome of interactions between E. willamettei and T. pacificus may be affected by grape cultivar, growing region, a combination of cultivar and region-specific differences, or size and timing of vine infestations with E. willamettei. In Thompson Seedless vineyards, vine infestation with E. willamettei would be most useful in increasing the effectiveness of the predatory mite M. occidentalis in controlling T. pacificus, primarily through an elevated predatory mite abundance prior to the development of large T. pacificus populations.

Wolbachia in a Predator–Prey System: 16S Ribosomal Dna Analysis of Two Phytoseiids (Acari: Phytoseiidae) and Their Prey (Acari: Tetranychidae)

Using specific polymerase chain reaction (PCR) primers, the 5' region of Wolbachia 16S ribosomal DNA from the predatory mite Metaseiulus occidentalis (Nesbitt) and the twospotted spider mite, Tetranychus urticae Koch, was amplified. Because the prey contains Wolbachia , a method to eliminate amplification of transient Wolbachia from the gut contents was necessary. We found that if the otherwise uninfected phytoseiid Amblyseius reductus Wainstein was fed spider mite prey containing Wolbachia , a positive PCR signal was detectable immediately after feeding, but not 4 h later. M. occidentalis remained positive for Wolbachia by the PCR even 48 h after feeding, although a stronger signal was present at 24 h or less. Wolbachia DNA could be amplified from the predator's eggs, suggesting it is transovarially transmitted and a stable symbiont in this predatory mite. All but 1 of the laboratory colonies of M. occidentalis tested were positive for Wolbachia by the PCR, including those from other laboratories. One fresh collection of M. occidentalis and their prey Panonychus ulmi (Koch) were tested immediately and again 5 d after collection from the field, but a positive PCR signal was never detected. A field-collected sample of T. urticae did not test positive for Wolbachia , although a Wolbachia -specific signal was detected in a population of the strawberry spider mite, T. turkestani Ugarov & Nikolski, collected simultaneously from the same field. PCR products from 1 adult female of the Russian Select strain of M. occidentalis , 60 eggs of the COS strain of M. occidentalis , and 1 male T. urticae were directly sequenced. Phylogenetic analyses placed them within the same clade as Wolbachia from insects, clustered together with the type species, Wolbachia pipientis Hertig, from Culex pipiens L. The Wolbachia from these mites was not similar to Wolbachia persica Suiter & Weiss from another acarine, the fowl tick, Argas persicus (Oken). The sequence similarity between the mite and insect Wolbachia provides more evidence for the horizontal transfer of this microorganism between diverse arthropods.