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Arthropod genes are made of deoxyribonucleic acid (DNA) and are located in chromosomes that consist of proteins, RNA, and DNA. DNA is a polymer of nucleotides (nt). Each nucleotide consists of a pentose sugar, one of four nitrogenous bases, and a phosphoric acid component. DNA consists of two complementary strands in a helix form. Pairing of the nitrogenous bases adenine (A) with thymine (T) and cytosine (C) with guanine (G) on the two complementary strands occurs by hydrogen bonding. A pairs with T by two hydrogen bonds, and C pairs with G by three hydrogen bonds. DNA has chemically distinct 5′ and 3′ ends, and the two strands are antiparallel, with one strand running in the 5′ to 3′ direction and the other strand running in the 3′ to 5′ direction. The antiparallel orientation of the two strands creates a special problem when the DNA is duplicated or replicated during mitosis or meiosis. Genetic information in protein-coding genes is determined by the sequence of nitrogenous bases (A, T, G, C) in one of the strands, with a three-base (triplet) codon designating an amino acid. The genetic code is degenerate, meaning that more than one codon specifies most amino acids. The genetic information is expressed when DNA is transcribed into pre-messenger RNA (pre-mRNA) that is processed into mRNA and then translated into polypeptides. Most insect genes have intervening noncoding sequences (introns) that must be removed from the primary RNA molecule before translation into the protein can occur. Efficient and accurate replication of DNA must occur at each cell division, or the cell or organism may not survive. DNA replication is semiconservative, i.e., one of the nucleotide strands of each new DNA molecule is new and the other nucleotide strand is old in each “cell generation.” The new DNA strand is complementary to the parental (or template) strand. DNA replication occurs in one direction only, from the 5′ to the 3′ end of the strand, and thus replication takes place differently on the two antiparallel strands. Replication on the “leading strand” can occur in the 5′ to 3′ direction in a continuous manner. DNA replication on the other strand, the “lagging strand,” occurs in short segments (Okazaki fragments) because the DNA runs in the 3′ to 5′ direction. Subsequently, the Okazaki fragments must be ligated together. Replication of DNA in chromosomes begins at multiple sites called origins of replication along the chromosome, and it involves many enzymes and proteins. Although DNA replication is usually highly accurate, errors in DNA replication, or mutations, can result from duplications, deletions, inversions, and translocations of nucleotides, all of which may affect the functioning of the resultant polypeptide. New combinations of genes can occur through recombination during meiosis.

Systematics is the study of phylogeny and taxonomy. Taxonomy can be divided into descriptive taxonomy and identification. DNA and genome sequences are suitable for systematics studies because they provide the most direct analysis of the genetic material possible and are unlikely to be confounded by life-stage or environmentally induced variability in morphology. Molecular techniques used include restriction analyses of DNA sequences and DNA sequencing of genes and entire genomes. Each method has virtues and limitations in the amount and type of information provided, their technical difficulties, and costs. There have been several significant controversies associated with using molecular techniques to study systematics and evolution. These include debates over the relative importance of molecular versus morphological data, the constancy of the molecular clock for evaluating time of divergence of taxa, the proper use of the terms homology and similarity, and the neutrality of DNA sequence variation. Another issue is how to resolve incongruencies between molecular- and morphology-based phylogenies and which phylogenetic method, which evolutionary model, and which DNA sequences should be used. The immense diversity of insects and their long evolutionary history provide challenges, especially with the analysis of deep evolutionary patterns. The availability of entire genomes of diverse arthropods will increasingly resolve many questions. With the use of molecular methods, evolutionary biologists and population geneticists are beginning to use common approaches to study both intraspecific and interspecific genetic diversity. The methodology used to analyze data and to develop phylogenetic trees continues to improve. However, considerable controversy may surround specific conclusions because the use of different analysis tools can result in different phylogenetic trees. In 2003, DNA barcoding was proposed as a method to obtain rapid and accurate identification of a broad range of organisms, including insects. The Consortium for the Barcode of Life was initiated in 2004, and in 2010 the International Barcode of Life project was established to develop an automated identification system based on a DNA barcode library of all eukaryotes. Projects for the Lepidoptera, Trichoptera, Formicidae, and Apidae were developed. The automated system requires advances in information technology for the huge datasets produced and one (BOLD) is freely available to all scientists. However, even Barcoding has limitations and its validity has been questioned.

Genetic information in an organism is expressed in three classes of genes: 1) structural (protein-coding) genes that are transcribed into messenger RNA (mRNA) and translated into polypeptides; 2) genes that code for ribosomal RNA (rRNA), transfer RNA (tRNA), or other classes of small RNAs, in which the transcription product is used directly; and 3) regulatory sites that are not transcribed but that serve as recognition sequences for proteins involved in DNA replication, transcription, and repair. Protein-coding genes in eukaryotic organisms are transcribed from DNA into pre-messenger RNAs (pre-mRNAs) that then are processed into mRNA. Processing of mRNA involves splicing to remove introns; mRNA also is capped and methylated at the 5′ end, and most mRNAs are polyadenylated at the 3′ end. The information in the mRNA then is translated into proteins via protein synthesis in ribosomes. A ribosome begins protein synthesis once the 5′ end of an mRNA is inserted into it. A lengthening polypeptide chain is produced and, once the 5′ end of the mRNA emerges from a ribosome, the mRNA can attach to a second ribosome and a second identical polypeptide can be synthesized. The assembly of amino acids into a peptide starts at the amino end and terminates at the carboxyl end. Amino acids are carried to the ribosome by transfer RNAs (tRNAs). The tRNAs are held so their anticodons form base pairs with complementary codons of the mRNA. One tRNA may recognize more than one codon because the genetic code is degenerate. According to the “wobble hypothesis,” the initial two bases of the mRNA codon pair according to base-pairing rules, but the third base may pair with any one of several bases. Protein synthesis occurs in the ribosomes that located in the endoplasmic reticulum of the cytoplasm. Once proteins are produced, they are transported into the Golgi apparatus where they are processed and transported to their ultimate destination. The protein must be folded and, sometimes, assembled into multiprotein complexes. Folding may require the assistance of other proteins called molecular chaperones. Gene regulation in insects and other eukaryotes is complex, diverse, and the subject of intensive research. Much of the DNA once labeled as “junk” or noncoding we now know is transcribed into RNAs that are involved in gene regulation and development. Protein-coding genes may be amplified or rearranged to increase the amount of gene product. Protein-coding genes may be regulated by being methylated. Activator proteins, hormones, enhancers and noncoding RNAs (ncRNAs) affect transcription. Alternative splicing, alternative promoters, and translational control are used in gene regulation, as are ncRNAs. Insulators or boundary elements are naturally occurring DNA sequences that protect genes from position effects, establishing independent functional domains within the chromosome.

Metaseiulus occidentalis is an eyeless phytoseiid predatory mite employed for the biological control of agricultural pests including spider mites. Despite appearances, these predator and prey mites are separated by some 400 Myr of evolution and radically different lifestyles. We present a 152-Mb draft assembly of the M. occidentalis genome: Larger than that of its favored prey, Tetranychus urticae, but considerably smaller than those of many other chelicerates, enabling an extremely contiguous and complete assembly to be built—the best arachnid to date. Aided by transcriptome data, genome annotation cataloged 18,338 protein-coding genes and identified large numbers of Helitron transposable elements. Comparisons with other arthropods revealed a particularly dynamic and turbulent genomic evolutionary history. Its genes exhibit elevated molecular evolution, with strikingly high numbers of intron gains and losses, in stark contrast to the deer tick Ixodes scapularis. Uniquely among examined arthropods, this predatory mite’s Hox genes are completely atomized, dispersed across the genome, and it encodes five copies of the normally single-copy RNA processing Dicer-2 gene. Examining gene families linked to characteristic biological traits of this tiny predator provides initial insights into processes of sex determination, development, immune defense, and how it detects, disables, and digests its prey. As the first reference genome for the Phytoseiidae, and for any species with the rare sex determination system of parahaploidy, the genome of the western orchard predatory mite improves genomic sampling of chelicerates and provides invaluable new resources for functional genomic analyses of this family of agriculturally important mites.

WOS:000356451400022 This study was carried out to determine the effects of temperature, relative humidity (RH), and an additional food source (honey) on the survival of Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae) females under cold-storage conditions. Survival was evaluated after 2, 4, and 8 wk at 7 or 10 degrees C under 75 or 95% RH. At the end of each cold-storage interval, surviving females were transferred to bean leaf discs with Tetranychus urticae Koch (Prostigmata: Tetranychidae) as prey, and their longevity, total number of eggs, and number of eggs each female produced per day were recorded. The highest survival rate (78.3%) was observed after 2 wk at 10 degrees C and 95% RH without honey in the tube. Survival was next highest (75%) after 2 wk at 7 degrees C and 95% RH without honey in tube. Survival was 76.7% at 7 degrees C with 95% RH without honey after 4 wk. Survival was low after 8 wk at both 7 or 10 degrees C, with 0 and 13.3% survival, respectively, at 95% RH. Adult longevity, the total number of eggs deposited, and the average number of eggs per female per day were not significantly different between females held for 2 or 4 wk at 7 or 10 degrees C at 95% RH with or without honey. Based on these results, M. occidentalis can be cold stored at 7 and 10 degrees C at 95% RH for up to 4 wk, but adding honey provided no benefit to the females.

Knowledge about the effects of pesticides on biological control agents is required in order to successfully implement integrated pest management programs. The predatory mite Amblyseius swirskii Athias-Henriot has been used to control thrips, whiteflies, and broad mites in vegetable production; however, effects of fenpyroximate, an acaricide and insecticide used in vegetable crops, on A. swirskii have not been evaluated. The effect of four residual concentrations of fenpyroximate on A. swirskii females was measured under laboratory conditions including its effect on their fecundity and larval survival. Fresh residues of fenpyroximate were significantly toxic to adult females and larvae. Mortality increased and fecundity decreased as the concentration (0.026–0.208 ml/50 ml of water) and time after treatment (24–120 h) increased. Fifty percent of the larvae survived on the two lower concentrations (0.026 and 0.052 ml/50 ml of water) after 120 h.

Amblyseius swirskiiAthias-Henriot (Acari: Phytoseiidae) is a predatory mite used to control thrips (Thysanoptera), whiteflies (Bemisia tabaci Genn., Hemiptera: Aleyrodidae), and broad mites (BMs) (Polyphagotarsonemus latus Banks, Acari: Tarsonemidae). Dispersal of A. swirskii, using the ornamental pepper “Explosive Ember” as a banker plant was evaluated for control of BMs in high-tunnel peppers. Open-canopy plants (5 weeks old) versus closed-canopy plants (10-weeks old) were used to evaluate the effect of plant connectedness in A. swirskii dispersal, in the presence (two females per plant) and absence of BMs. Plots consisted of a single central banker plant and four bell peppers extending linearly north and south. Sets of all treatments were destructively sampled 1, 4, and 7 days after releasing A. swirskii. Within 24 h, A. swirskii dispersed four plants away from the banker plants (1 m), regardless of the state of the canopy. Canopy connectedness did increase the presence of A. swirskii on the crop plants. Predatory mite numbers on closed-canopy treatments doubled within the 7-day sampling period, whereas no significant increase was observed on open-canopy treatments. The presence of BMs had no significant effect on the movement of A. swirskii. The results suggest further experiments with A. swirskii and banker plants for control of BMs is warranted.

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.

Little is known about the process of sex determination at the molecular level in Metaseiulus occidentalis, a parahaploid species and natural enemy of phytophagous pest mites. Detailed knowledge of the sex-determination pathway could allow genetic manipulation of M. occidentalis to produce more female offspring, which could improve its effectiveness as a biological control agent. RNA interference is useful for assessing the function of putative sex-determination genes by reducing or eliminating gene expression. In many insect species the transformer-2 (tra-2) gene is an upstream regulatory element in the sex-determination cascade, and knockdown of tra-2 expression can alter the sex ratio. We assessed whether oral delivery of tra-2 double-stranded RNA to M. occidentalis virgin females would affect the sex of her progeny. Females that ingested tra-2 dsRNA produced significantly fewer eggs compared to control females suggesting that tra-2 is somehow involved in reproduction by females. However, the sex ratio of the few progeny that were laid was not altered, so it is unclear whether tra-2 is involved in sex determination. This is an initial step towards elucidating the molecular components of sex determination in M. occidentalis.

In two recent studies, we showed that females from a long-established Metaseiulus (Typhlodromus or Galendromus) occidentalis laboratory colony reared under crowded conditions for approximately 27 years produced equal numbers of male and female progeny. This contrasts with our previous results that showed the females from the same colony produced progeny with a female-biased sex ratio. These discrepant findings raised the possibility that dense rearing conditions can affect the sex-allocation plasticity in this important biological control agent. In the current study, we show that females from a newly collected M. occidentalis colony initially were capable of producing progeny with a female-biased sex ratio, but lost this ability over a 12-month period (43 generations) when reared under dense rearing conditions and provided with damaged prey. We demonstrate that females from this newly collected colony initially could adjust offspring sex ratio in response to both conspecific cues and cues produced by their damaged prey. The results suggest that dense rearing conditions, which are often used in commercial rearing facilities, may have detrimental effects on the reproductive fitness of M. occidentalis and, possibly, other predatory mites.

Hemicheyletia wellsina is a predator of several families of arthropod plant pests. Hemicheyletia wellsina females produce silk webbing that covers their egg clutches, but the function of the webbing is unknown. Experiments indicate the webbing can protect the eggs from predation, resulting in approximately a 71% increase in egg hatch compared to when silk was removed in the presence of the phytoseiid predator Metaseiulus occidentalis. Within 2–3 days after larvae hatch, they appear to no longer need protection, as 18 of 20 H. wellsina larvae captured and fed on the much larger adult M. occidentalis females. The silk also may regulate the relative humidity around the eggs.

The toxicity of 2 reduced-risk pesticides, 2% horticultural oil with 0.05% Silwet L-77 and Grandevo (Chromobacterium subtsugae Strain PRAA4-1T), to 2 predators: Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae) and Hemicheyletia wellsina DeLeon (Acari: Cheyletidae), and 3 orchid pests: the two-spotted spider mite Tetranychus urticae Koch (Prostigmata: Tetranychidae), the phalaenopsis mite, Tenuipalpus pacificus Baker (Acari: Tenuipalpidae), and the longtailed mealybug Pseudococcus longispinus (Targioni-Tozzetti) (Hemiptera: Pseudococcidae) were tested. Grandevo did not kill either predator, and it failed to suppress populations of T. urticae and P. longispinus, but it reduced T. pacificus by 84%. The Silwet and horticultural oil mixture caused mortality of at least 82% in all 5 species tested.

Raoiella indica Hirst (Acari: Tenuipalpidae), a pest of coconut and other species of palms, recently invaded the Western Hemisphere. Amblyseius largoensis (Muma) (Acari: Phytoseiidae), is a predatory mite found associated with R. indica in different parts of the world. Exclusion and release tactics were used to obtain coconut palms with varying levels of A. largoensis in order to quantify their effects on R. indica densities. Four treatments consisting of 4 rates of release of A. largoensis females (0 = control, 1:10, 1:20 and 1:30 A. largoensis: R. indica) were tested. The releases of A. largoensis resulted in a significant reduction of R. indica densities and less damaged leaf area in the treated coconut palms compared to the controls within 3 months. The largest pest density reduction (~92%) was observed at the highest predator release rate (1:10 A. largoensis: R. indica). The other 2 release rates (1:20 and 1:30 A. largoensis: R. indica) caused significant and equivalent reductions in pest densities (55 and 43%, respectively). Results of this study support the hypothesis that A. largoensis is an important mortality factor of R. indica and should be considered as a key biological control agent in IPM programs targeting R. indica.

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 7 days 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.

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.

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.