Adaptive divergence and post-zygotic barriers to gene flow between sympatric populations of a herbivorous mite

Plant-herbivore interactions promote the generation and maintenance of both plant and herbivore biodiversity. The antagonistic interactions between plants and herbivores lead to host race formation: the evolution of herbivore types specializing on different plant species, with restricted gene flow between them. Understanding how ecological specialization promotes host race formation usually depends on artificial approaches, using laboratory experiments on populations associated with agricultural crops. However, evidence on how host races are formed and maintained in a natural setting remains scarce. Here, we take a multidisciplinary approach to understand whether populations of the generalist spider mite Tetranychus urticae form host races in nature. We demonstrate that a host race co-occurs among generalist conspecifics in the dune ecosystem of The Netherlands. Extensive field sampling and genotyping of individuals over three consecutive years showed a clear pattern of host associations. Genome-wide differences between the host race and generalist conspecifics were found using a dense set of SNPs on field-derived iso-female lines and previously sequenced genomes of T. urticae. Hybridization between lines of the host race and sympatric generalist lines is restricted by post-zygotic breakdown, and selection negatively impacts the survival of generalists on the native host of the host race. Our description of a host race among conspecifics with a larger diet breadth shows how ecological and reproductive isolation aid in maintaining intra-specific variation in sympatry, despite the opportunity for homogenization through gene flow. Our findings highlight the importance of explicitly considering the spatial and temporal scale on which plant-herbivore interactions occur in order to identify herbivore populations associated with different plant species in nature. This system can be used to study the underlying genetic architecture and mechanisms that facilitate the use of a large range of host plant taxa by extreme generalist herbivores. In addition, it offers the chance to investigate the prevalence and mechanisms of ecological specialization in nature.

High genetic diversity in a 'recent outbreak' spider mite, Tetranychus pueraricola, in mainland China

Tetranychus pueraricola is a newly reported spider mite that occurs frequently in mainland China. It is possible that this species was introduced from elsewhere and became a serious pest recently. However, the correct identification of red-pigmented spider mites has repeatedly proven problematic. There is also the possibility that T. pueraricola in China was long misidentified as its sibling species, Tetranychus urticae (red form). To test which of these two scenarios is the more likely, individuals from 14 populations of T. pueraricola and five populations of T. urticae (red form) in China were sampled and genotyped using mitochondrial COI and microsatellite loci. Unlike a recent invasive species, the genetic diversity of T. pueraricola was very high with high mitochondrial genetic diversity (16 haplotypes), high effective alleles (Ne = 2.038 ± 0.081) and expected heterozygosity (He = 0.395 ± 0.016). Surprisingly, we found that all T. urticae (red form) populations shared only one mitochondrial haplotype and showed quite low genetic diversity (Ne = 1.443 ± 0.055; He = 0.234 ± 0.025) which was even lower than that of the green form of T. urticae in mainland China from a previous study. We did not detect significant signals of recent bottlenecks for most populations from both species. These results suggest T. pueraricola is unlikely to be a recent invasive pest but a species that has existed in China for a long time. It is probable that T. pueraricola in China has long been misidentified as T. urticae (red form).

Identification of spider-mite species and their endosymbionts using multiplex PCR

Spider mites of the genus Tetranychidae are severe crop pests. In the Mediterranean a few species coexist, but they are difficult to identify based on morphological characters. Additionally, spider mites often harbour several species of endosymbiotic bacteria, which may affect the biology of their hosts. Here, we propose novel, cost-effective, multiplex diagnostic methods allowing a quick identification of spider-mite species as well as of the endosymbionts they carry. First, we developed, and successfully multiplexed in a single PCR, primers to identify Tetranychus urticae, T. evansi and T. ludeni, some of the most common tetranychids found in southwest Europe. Moreover, we demonstrated that this method allows detecting multiple species in a single pool, even at low frequencies (up to 1/100), and can be used on entire mites without DNA extraction. Second, we developed another set of primers to detect spider-mite endosymbionts, namely Wolbachia, Cardinium and Rickettsia in a multiplex PCR, along with a generalist spider-mite primer to control for potential failure of DNA amplification in each PCR. Overall, our method represents a simple, cost-effective and reliable method to identify spider-mite species and their symbionts in natural field populations, as well as to detect contaminations in laboratory rearings. This method may easily be extended to other species.

Expression characteristics of two novel cytochrome P450 genes involved in fenpropathrin resistance in Tetranychus cinnabarinus (Boisduval)

The carmine spider mite, Tetranychus cinnabarinus, which is also considered as the red form of Tetranychus urticae, is one of the most serious mite pests on crops. It is capable of rapidly developing resistance to acaricides, and has caused difficulty in controlling. However, the resistance mechanism of this mite remains unclear at molecular level. As a member of main detoxification enzymes, cytochrome P450 monooxygenases (CYPs or P450s) play important roles in the development of acaricide resistance in arthropods. In this study, two novel P450 genes (CYP389B1 and CYP392A26) were identified and characterized from T. cinnabarinus. The opening reading frames (ORFs) of CYP389B1 and CYP392A26 contained 1545 and 1488 nucleotides, which encode 514 and 495 amino acids, respectively. Phylogenetic analysis showed that CYP389B1 and CYP392A26 were most closely related to CYP389B1 and CYP392A4 from T. urticae, respectively. When treated with piperonyl butoxide (PBO), an inhibitor of P450s, the resistance ratio of fenpropathrin-resistant (FeR) strain decreased from 101- to 75-fold, which suggested a correlation between P450 and fenpropathrin-resistance in T. cinnabarinus. Furthermore, constitutive over-expressions of CYP389B1 and CYP392A26 were detected in FeR strain. Meanwhile, the expressions of CYP389B1 and CYP392A26 were inducible in FeR strain after treatment in 6, 12 and 24 h with LC30 of fenpropathrin; especially, the expression of CYP392A26 increased to a markedly high level (20.88-fold higher than in the control) after treatment in 6 h. However, there was no significant difference between treatment and control in susceptible strain. Furthermore, stage specific expression profiles of these two genes did not show significant difference among developing stages, except for eggs, in which the mRNA levels were quite low. The results indicate that CYP389B1 and CYP392A26 were involved in the fenpropathrin-resistance in T. cinnabarinus, and the expression of CYP392A26 was more sensitive to fenpropathrin stress. These findings provide clues for further elucidating the function and regulation mechanism of these two cytochrome P450 genes in T. cinnabarinus.

Phylogenetic analysis of the spider mite sub-family Tetranychinae (Acari: Tetranychidae) based on the mitochondrial COI gene and the 18S and the 5' end of the 28S rRNA genes indicates that several genera are polyphyletic

The spider mite sub-family Tetranychinae includes many agricultural pests. The internal transcribed spacer (ITS) region of nuclear ribosomal RNA genes and the cytochrome c oxidase subunit I (COI) gene of mitochondrial DNA have been used for species identification and phylogenetic reconstruction within the sub-family Tetranychinae, although they have not always been successful. The 18S and 28S rRNA genes should be more suitable for resolving higher levels of phylogeny, such as tribes or genera of Tetranychinae because these genes evolve more slowly and are made up of conserved regions and divergent domains. Therefore, we used both the 18S (1,825-1,901 bp) and 28S (the 5' end of 646-743 bp) rRNA genes to infer phylogenetic relationships within the sub-family Tetranychinae with a focus on the tribe Tetranychini. Then, we compared the phylogenetic tree of the 18S and 28S genes with that of the mitochondrial COI gene (618 bp). As observed in previous studies, our phylogeny based on the COI gene was not resolved because of the low bootstrap values for most nodes of the tree. On the other hand, our phylogenetic tree of the 18S and 28S genes revealed several well-supported clades within the sub-family Tetranychinae. The 18S and 28S phylogenetic trees suggest that the tribes Bryobiini, Petrobiini and Eurytetranychini are monophyletic and that the tribe Tetranychini is polyphyletic. At the genus level, six genera for which more than two species were sampled appear to be monophyletic, while four genera (Oligonychus, Tetranychus, Schizotetranychus and Eotetranychus) appear to be polyphyletic. The topology presented here does not fully agree with the current morphology-based taxonomy, so that the diagnostic morphological characters of Tetranychinae need to be reconsidered.

Population survey of phytoseiid mites and spider mites on peach leaves and wild plants in Japanese peach orchard

A population survey of phytoseiid mites and spider mites was conducted on peach leaves and wild plants in Japanese peach orchards having different pesticide practices. The phytoseiid mite species composition on peach leaves and wild plants, as estimated using quantitative sequencing, changed during the survey period. Moreover, it varied among study sites. The phytoseiid mite species compositions were similar between peach leaves and some wild plants, such as Veronica persica, Paederia foetida, Persicaria longiseta, and Oxalis corniculata with larger quantities of phytoseiid mites, especially after mid-summer. A PCR-based method to detect the ribosomal ITS sequences of Tetranychus kanzawai and Panonychus mori from phytoseiid mites was developed. Results showed that Euseius sojaensis (specialized pollen feeder/generalist predator) uses both spider mites as prey in the field.

PCR-RFLP analysis for identification of Tetranychus spider mite species (Acari: Tetranychidae)

A polymerase chain reaction (PCR)-restriction fragment length polymorphism (PCR-restriction fragment-length polymorphism)-based method for species identification was applied to 14 Tetranychus spider mite species, which were dominant species intercepted at Japanese import plant quarantine. We sequenced the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA (rDNA), which included the partial ends of the 18S and 28S ribosomal RNA genes, 5.8S ribosomal RNA gene, and two internal transcribed spacers (ITS1 and ITS2) for 15 populations of the 14 species. We analyzed the recognition sites of four restriction endonucleases, which had been proposed for discrimination of Japanese Tetranychus species, and constructed a scheme for Tetranychus species identification by PCR-restriction fragment-length polymorphism. We then applied the scheme to 245 individuals from 199 populations, most of them were from foreign countries. As a result, all 14 species were correctly identified using PCR-restriction fragment-length polymorphism. This demonstrates the usefulness of the PCR-restriction fragment-length polymorphism method for the worldwide identification of Tetranychus species.

Diversity of Wolbachia in natural populations of spider mites (genus Tetranychus): evidence for complex infection history and disequilibrium distribution

Wolbachia are endosymbiotic bacteria that commonly infect arthropods and cause reproductive disorders in host. Within several Tetranychus species, Wolbachia have been detected and shown to affect their reproduction. However, little is known about their transmission and distribution patterns in natural populations of Tetranychus species. Here, we used multilocus sequence typing to confirm Wolbachia infection status and examined the relationship between Wolbachia infection status and host phylogeny, mitochondrial diversity, and geographical range in five Tetranychus species (Tetranychus truncatus, Tetranychus urticae, Tetranychus pueraricola, Tetranychus phaselus, and Tetranychus kanzawai) from 21 populations in China. The prevalence of Wolbachia within the five Tetranychus species ranged from 31.4 to 100 %, and the strains were remarkably diverse. Together, these observations indicate that Wolbachia was introduced to these populations on multiple separate occasions. As in other arthropods, the same Tetranychus species can accommodate very different strains, and identical Wolbachia occasionally infect different species. These observations suggest that Wolbachia are transmitted both vertically and horizontally. Horizontally, transmission is probably mediated by the host plants. The distribution patterns of Wolbachia were quite different among populations of the same species, suggesting that the dynamics of Wolbachia in nature may be affected by ecological and other factors.

Spider mite control and resistance management: does a genome help?

The complete genome of the two-spotted spider mite, Tetranychus urticae, has been reported. This is the first sequenced genome of a highly polyphagous and resistant agricultural pest. The question as to what the genome offers the community working on spider mite control is addressed.

DNA-based identification of spider mites: molecular evidence for cryptic species of the genus Tetranychus (Acari: Tetranychidae)

Spider mites are difficult to identify because they are very small and have a limited number of diagnostic characters. Most species of the spider mite genus Tetranychus in Japan are morphologically similar, differing only in the diameter of the aedeagal knob in males. Because this genus contains many important pests, the unambiguous identification of species is crucial for effective pest management and quarantine procedures. DNA-based methods could complement the morphological methods. We examined whether Tetranychus species in Japan could be identified by DNA sequences using the internal transcribed spacer region of nuclear ribosomal DNA and the cytochrome c oxidase subunit I gene of mitochondrial DNA. We determined sequences of the 13 known Tetranychus species in Japan. We could identify 10 of the 13 species in the internal transcribed spacer tree. In the cytochrome c oxidase subunit I tree, we could identify all 13 known Tetranychus species in Japan. Although Tetranychus kanzawai Kishida and T. parakanzawai Ehara were identified by DNA sequences, they were clearly separated into two monophyletic clades each, indicating that a cryptic species existed in each species.

The cys-loop ligand-gated ion channel gene family of Tetranychus urticae: implications for acaricide toxicology and a novel mutation associated with abamectin resistance

The cys-loop ligand-gated ion channel (cysLGIC) super family of Tetranychus urticae, the two-spotted spider mite, represents the largest arthropod cysLGIC super family described to date and the first characterised one within the group of chelicerates. Genome annotation, phylogenetic analysis and comparison of the cysLGIC subunits with their counterparts in insects reveals that the T. urticae genome encodes for a high number of glutamate- and histamine-gated chloride channel genes (GluCl and HisCl) compared to insects. Three orthologues of the insect γ-aminobutyric acid (GABA)-gated chloride channel gene Rdl were detected. Other cysLGIC groups, such as the nAChR subunits, are more conserved and have clear insect orthologues. Members of cysLGIC family mediate endogenous chemical neurotransmission and they are prime targets of insecticides. Implications for toxicology associated with the identity and specific features of T. urticae family members are discussed. We further reveal the accumulation of known and novel mutations in different GluCl channel subunits (Tu_GluCl1 and Tu_GluCl3) associated with abamectin resistance in T. urticae, and provide genetic evidence for their causality. Our study provides useful toxicological insights for the exploration of the T. urticae cysLGIC subunits as putative molecular targets for current and future chemical control strategies.

Molecular-based identification and phylogeny of Oligonychus species (Acari: Tetranychidae)

The genus Oligonychus has been morphologically divided into two groups based on the direction of curvature of the aedeagus and includes some morphologically similar species that are difficult to distinguish. To develop DNA-based methods for identifying Oligonychus species and to determine the phylogenetic relationships among them, we examined the cytochrome c oxidase subunit I gene of mitochondrial DNA and the internal transcribed spacer and 28S regions of nuclear ribosomal RNA gene for 17 species. Based on the genetic distances (p-distances) of the three DNA regions, the range of intraspecific divergence was found to be below (and not overlap) the range of interspecific divergence, which allowed the 17 species to be discriminated correctly, consistent with their classification based on morphology. Phylogenetic trees constructed by neighbor-joining and Bayesian methods clearly showed two clades, consisting of species whose aedeagi curve ventrally and dorsally, respectively. Three Oligonychus species inhabiting gramineous plants formed clearly defined subclades.

First record of the carmine spider mite, Tetranychus urticae, infesting Withania somnifera in India

During April-June 2010, red two-spotted carmine spider mites Tetranychus urticae Koch (Trombidiformes: Tetranychidae) were found on aerial apical parts of Ashwagandha Withania somnifera (L.) Dunal (Solanales: Solanaceae) plants in the Amritsar District of Punjab Province in the North Indian plains. The mites fed on the leaves, making them shiny white in color, which gradually dried off and were later shed. The pest was identified as T. urticae. To best of our knowledge, this is the first record of this pest infesting W. somnifera in India.

Phytoseiid mite species composition in Japanese peach orchards estimated using quantitative sequencing

We attempted a population survey of spider mites and phytoseiid mites in Japanese peach orchards with different pesticide practices; however, we had difficulty discriminating phytoseiid mites. To estimate phytoseiid mite species composition, ribosomal gene fragments were amplified from genomic DNA of five phytoseiid mite species using PCR. Cloning and nucleotide sequencing of amplified fragments identified species-specific polymorphic sites. Newly amplified fragments from recombinant plasmids were mixed in various ratios to produce standard DNA template mixtures. After direct sequencing, the signal ratios between two nucleotides at each species-specific polymorphic site were calculated and shown against the corresponding expected ratios. Quadratic regression equations were used to estimate the phytoseiid mite species composition. Results showed that the phytoseiid mite species composition changed during the survey period and varied among study sites.

A critical review on some closely related species of Tetranychus sensu stricto (Acari: Tetranychidae) in the public DNA sequences databases

Taxonomic misidentification of the specimens used to obtain DNA sequences is a growing problem reported for different groups of organisms, which threatens the utility of the deposited sequences in public DNA databases. This paper provides new evidence of misidentifications in molecular DNA public databases in phytophagous mites of the Tetranychidae family belonging to the group Tetranychus (Tetranychus). Several species in this group are of economic and quarantine importance in agriculture and among them Tetranychus urticae, a highly polyphagous mite causing outbreaks in many crops worldwide, is certainly the most studied. We analyzed and evaluated the identity of 105 GenBank accessions of ITS2 rDNA and 138 COI mtDNA sequences which were deposited as T. urticae and those of 14 other taxa morphologically closely related to Tetranychus sensu stricto. In addition, ITS2 and COI sequences of 18 T. urticae samples collected for this study and identified by morphological criteria, were generated and included in the analyzed dataset. Among the deposited sequences in the GenBank database, numerous cases of apparently mistaken identities were identified in the group Tetranychus s. str., especially between T. urticae, T. cinnabarinus, T. kanzawai and T. truncatus. Unreliable sequences (misidentified or dubious) were estimated at nearly 30%. In particular the analysis supports the invalidity of the controversial species status of T. cinnabarinus. More generally, it highlights the need of using combined morphological and molecular approaches to guarantee solid species diagnostics for reliable sequence accessions in public databases.

Effects of Wolbachia on mtDNA variation and evolution in natural populations of Tetranychus urticae Koch

We investigated the effects of Wolbachia infection on mtDNA variation in spider mites by sequencing a portion of the mitochondrial cytochrome oxidase I (COI) gene from 198 individuals of known infection status. Four Wolbachia strains were described in the current study, namely wUrtOri1, wUrtOri2, wUrtOri3 and wUrtCon1. As predicted, the haplotype and nucleotide diversity were lower in infected individuals than in uninfected individuals. However, these mtDNA haplotype data are not entirely concordant with the surface protein of wolbachia (wsp) sequence data and both infected and uninfected individuals were found of the same haplotype. Although values of Tajima's D and Fu & Li's F were consistently less than zero for most infected groups, McDonald-Kreitman tests suggested that the patterns of variation were different from those expected under neutrality in only the uninfected group. Thus, the neutrality tests do not show a clear effect of Wolbachia infection on patterns of mtDNA variation and substitution in spider mites.

Restriction fragment length polymorphism catalog for molecular identification of Japanese Tetranychus spider mites (Acari: Tetranychidae)

Species identification is a basic issue in biosecurity. Polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) is a useful molecular diagnostic tool for species identification. However, the lack of transferability of data has been a serious shortcoming of this method. A RFLP catalog, i.e., a graph of PCR-RFLP patterns expected from sequence data, was devised as a tool to facilitate PCR-RFLP data sharing among laboratories. Twelve species of Tetranychus spider mites have been recorded in Japan to date. In this study, we analyzed DNA sequences of the internal transcribed spacer (ITS) region in nuclear ribosomal DNA of 11 Tetranychus species. For the species identification using PCR-RFLP, we chose six candidates from 131 restriction endonucleases and developed an RFLP catalog of all known Japanese Tetranychus species except Tetranychus neocaledonicus André. The RFLP catalog revealed that most Tetranychus species had diagnostic restriction fragments. The RFLP catalog is transferable and simple molecular diagnostic tool, and it has the ability to add more species and newly found intraspecific variations. Therefore, we believe that the RFLP catalog will contribute to biosecurity as a practical diagnostic tool for species identification of spider mites.

Life history of the predatory mite Phytoseiulus fragariae on Tetranychus evansi and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) at five temperatures

Tetranychus evansi Baker and Pritchard and Tetranychus urticae Koch (Acari: Tetranychidae) are important pests of Solanaceae in many countries. Several studies have demonstrated that T. urticae is an acceptable prey to many predatory mites, although the suitability of this prey depends on the host plant. T. evansi, has been shown to be an unfavorable prey to most predatory mites that have been tested against it. The predator Phytoseiulus fragariae Denmark and Schicha (Acari: Phytoseiidae) has been found in association with the two species in Brazil. The objective of this work was to compare biological parameters of P. fragariae on T. evansi and on T. urticae as prey. The study was conducted under laboratory conditions at 10, 15, 20, 25 and 30 degrees C. At all temperatures, survivorship was lower on T. evansi than on T. urticae. No predator reached adulthood at 10 degrees C on the former species; even on the latter species, only about 36% of the predators reached adulthood at 10 degrees C. For both prey, in general, duration of each life stage was shorter, total fecundity was lower and intrinsic rate of population increase (r(m)) was higher with increasing temperatures. The slower rate of development of P. fragariae on T. evansi resulted in a slightly higher thermal requirement (103.9 degree-days) on that prey than on T. urticae (97.1 degree-days). The values of net reproduction rate (R (0)), intrinsic rate of increase (r(m)) and finite rate of increase (lambda) were significantly higher on T. urticae, indicating faster population increase of the predator on this prey species. The highest value of r(m) of the predator was 0.154 and 0.337 female per female per day on T. evansi and on T. urticae, respectively. The results suggested that P. fragariae cannot be considered a good predator of T. evansi.

Spider mite (Acari: Tetranychidae) mitochondrial COI phylogeny reviewed: host plant relationships, phylogeography, reproductive parasites and barcoding

The past 15 years have witnessed a number of molecular studies that aimed to resolve issues of species delineation and phylogeny of mites in the family Tetranychidae. The central part of the mitochondrial COI region has frequently been used for investigating intra- and interspecific variation. All these studies combined yield an extensive database of sequence information of the family Tetranychidae. We assembled this information in a single alignment and performed an overall phylogenetic analysis. The resulting phylogeny shows that important patterns have been overlooked in previous studies, whereas others disappear. It also reveals that mistakes were made in submitting the data to GenBank, which further disturbed interpretation of the data. Our total analysis clearly shows three clades that most likely correspond to the species T. urticae, T. kanzawai and T. truncatus. Intraspecific variation is very high, possibly due to selective sweeps caused by reproductive parasites. We found no evidence for host plant associations and phylogeographic patterns in T. urticae are absent. Finally we evaluate the application of DNA barcoding.

Search for effective natural enemies of Tetranychus evansi (Acari: Tetranychidae) in northwest Argentina

The mite Tetranychus evansi Baker & Pritchard (Tetranychidae) probably originated in South America. Because of its importance as a tomato pest in Africa, an extensive project has been conducted to detect potentially effective natural enemies in South America for the classical biological control of the pest in Africa. A search for the natural enemies of T. evansi was conducted in the Province of Tucumán, northwestern Argentina, in December 2004, and this report describes the results. One hundred predatory mites of the family Phytoseiidae referring to 11 species were collected on 11 examined species of solanaceous plants. The most abundant phytoseiid species collected were Neoseiulus californicus (McGregor) and Euseius concordis (Chant). Adults and immatures of those species, as well as of Neoseiulus idaeus Denmark & Muma, Phytoseiulus fragariae Denmark & Schicha and Proprioseiopsis cannaensis (Muma) were found in association with T. evansi, suggesting that they were developing on the pest. However, because of the possible biological differences between populations of a given species, biological studies evaluating T. evansi as a prey for those predators seem desirable.

ITS2 sequences as barcodes for identifying and analyzing spider mites (Acari: Tetranychidae)

The use of DNA barcodes, short DNA sequences from a standardized region of the genome, has recently been proposed as a tool to facilitate species identification and discovery. Here we show that second internal transcribed spacer of nuclear ribosomal DNA (rDNA-ITS2) barcodes effectively discriminate among 16 species of spider mites (Acari: Tetranychidae) from Israel. The barcode sequences of each species were unambiguously distinguishable from all other species and formed distinct, nonoverlapping monophyletic groups in the maximum-parsimony tree. Sequence divergences were generally much greater between species than within them. Using a 0.02 (2%) threshold for species diagnosis in our data set, 14 out of 16 species recognized by morphological criteria would be accurately identified. The only exceptions involved the low divergence, 0.011-0.015 (1.1-1.5%), between Tetranychus urticae and Tetranychus turkestani, where speciation may have occurred only recently. Still, these species had fixed alternative rDNA-ITS2 variants, with five diagnostic nucleotide substitutions. As a result, we tentatively conclude that rDNA-ITS2 sequence barcodes may serve as an effective tool for the identification of spider mite species and can be applicable as a diagnostic tool for quarantine and other pest management activities and decision-making. We predict that our work, together with similar efforts, will provide in the future the platform for a uniform, accurate, practical and easy-to-use method of spider mite species identification.

Search for effective natural enemies of Tetranychus evansi in south and southeast Brazil

Tetranychus evansi Baker & Pritchard is an important pest of Solanaceae in several countries. Introduced accidentally to Africa, it presently occurs in many countries of that continent. In some of them, it is considered a key pest. The suspected area of origin of this mite is South America. The objective of the present study was to identify phytoseiid mites on solanaceous plants in association with T. evansi in south and southeast Brazil for introduction in the African continent for use in a classic biological control program. Almost 1,400 predatory mites of the family Phytoseiidae were collected, on 22 solanaceous species. The Amblyseiinae were the most diverse group in this study. Twenty-three of the species found belong to this subfamily, while only three belong to the Typhlodrominae and two to the Phytoseiinae. The most abundant and most frequent phytoseiid species were Phytoseius guianensis De Leon and Galendromus annectens (De Leon) of the Phytoseiinae and Typhlodrominae, respectively. The most frequent and abundant species of Amblyseiinae was Neoseiulus tunus (De Leon). Phytoseius guianensis and N. tunus were never found in association with T. evansi and G. annectens was found only once in association with it. Two factors suggested Phytoseiulus longipes Evans as the most promising predator found in this study. It could walk very well on tomato leaves infested by T. evansi, without being hampered by the profuse webbing produced by the prey and by the trichomes. In addition, several specimens of both sexes including eggs and nymphs of the predator were found associated with T. evansi on three different plant species and in two different periods of the year, when T. evansi was the only arthropod present on the leaves.

[Effects of corn cultivar on Tetranychus truncatus ehara (Acarina: Tetranychidae) population parameters]

The laboratory study at 28 degrees C showed that on four different corn cultivars, the durations of ovum, nymph and pre-oviposition, adult longevity, fecundity, egg production per day, net reproductive rate (R0), finite rate of increase (lambda), intrinsic rate of increase (rm), mean generation time (T), and the days needed to double population size (DDP) of Tetranychus truncatus were significantly different. The hatching rate on Zea mays cv. Zhongdan 2, Nongda 108, Chidan 202 and Badan 3 was 95.8%, 94.0%, 90.0% and 84.0%, and the survival rate on these cultivars was 90.5%, 86.0%, 84.0%, and 72.0%, respectively. All the survival curves were of Deevey I . The net reproductive rate (R0) was the highest on Zhongdan 2, and the lowest on Badan 3. The mite displayed a decreasing preference in order of Zhongdan 2 > Nongda 108 > Chidan 202 > Badan 3.

Predation by Allothrombium pulvinum on the spider mites Tetranychus urticae and Amphitetranychus viennensis: predation rate, prey preference and functional response

The deutonymphs of Allothrombium pulvinum Ewing (Acari: Trombidiidae) are among the most important natural enemies of spider mites in North, North East and West Iran. In this study, maximum predation rate and preference experiments were conducted with A. pulvinum deutonymphs on apple leaf discs, to determine their preference for either of two spider mite species: Amphitetranychus viennensis (Zacher) and Tetranychus urticae Koch (Acari: Tetranychidae). Maximum predation rate tests showed that the predatory mite consumed more eggs and females of T. urticae than of A. viennensis. Furthermore, the Manly's preference index for eggs and females of T. urticae confirmed that T. urticae were the preferred prey. The functional response of A. pulvinum deutonymphs on females of T. urticae was examined over a 24-h period. Predation of A. pulvinum deutonymphs presented with females of T. urticae followed a type III functional response. Estimated handling time for the predatory mites was 4.51 h and attack coefficient b, which describes the changes in attack rate with prey densities in a type III functional response, was 0.021.

Isolation, characterization, inheritance and linkage of microsatellite markers in Tetranychus kanzawai (Acari: Tetranychidae)

We isolated and characterized seven microsatellite markers in Tetranychus kanzawai (Acari: Tetranychidae). We also examined the conformity of the isolated markers to Mendelian laws and analyzed linkage among the microsatellite loci. All microsatellite markers fit expected 1:1 disomic segregation ratio and hence were inherited in a Mendelian manner. Significant pairwise linkage was detected in three pairs of microsatellite loci. These isolated microsatellite markers may become a powerful tool for the study of behavioral ecology, population genetics, and genome mapping of T. kanzawai.