Spider Mite Research Articles

Indirect effects of plasma-activated water irrigation on Tetranychus urticae populations

AbstractPlasma-activated water (PAW) is receiving increased attention as a booster of seed germination and seedling vigor, and some studies have described use of PAW to manage crop pathogens. Here, we examined physicochemical properties of two PAWs (referred to as PAW 6.0 and 9.4 min with atmospheric plasma jet) and assessed “their indirect effects” (applied as supplementary irrigation) on host suitability of tomato plants (Solanum lycopersicum L.) to two-spotted spider mites (Tetranychus urticae Koch). Exposure of water to cold plasma significantly lowered pH and increased concentrations of H2O2, NO2−, and NO3−. Supplementary PAW irrigations elicited significant increases in leaf composition of several elements (N, P, K S, Ca, and Mg), leaf reflectance, plant size, and trichome densities (except non-glandular trichomes on the adaxial surface). Preference bioassays revealed significant avoidance of settling and reduced oviposition by two-spotted spider mites on leaf discs from PAW-irrigated plants compared to those from untreated control plants. Performance bioassays showed a significant decrease in two-spotted spider mite populations on PAW-irrigated plants. Results presented in this study provide comprehensive support to the hypothesis that indirect effects of supplementary PAW irrigation significantly reduce host plant suitability to two-spotted spider mites. PAW 6.0 may be slightly better than PAW 9.4, and this difference in performance is discussed in this study. Applications of PAW as supplementary irrigation are likely highly compatible with other IPM tactics and should be considered an innovative and sustainable component in twenty-first-century pest management.

Metabolomic responses of tea [Camellia sinensis (L.) O. Kuntze] leaves to red spider mite [Oligonychus coffeae (Nietner)] and tea mosquito bug [Helopeltis theivora Waterhouse] infestation: a GC–MS-based study

BackgroundThe tea plant, Camellia sinensis (L.) O. Kuntze, is an evergreen leafy plant whose tender leaves are used in the manufacturing of the world’s second most consumed beverage—tea. The production and consumption of tea worldwide have continually increased over the decades. All parts of the plant—leaf, stem, root, flower and seed, are fed upon by insect pests. This study elucidates the metabolomic changes occurring in tea leaves in response to infestation by two major pests in tea gardens: red spider mites and tea mosquito bugs. These pests significantly impact both the quantity and quality of tea production. The secondary metabolites produced by the tea due to pest attack has been analysed using GC–MS analysis in the laboratory.ResultsMostly fatty acid derivatives were biosynthesized as secondary metabolites due to pest attack as revealed from the result. In both infestations, methyl stearate was found to be produced along with increased chromatographic peaks of compounds such as caffeine, methyl palmitate, methyl linoleate, and stigmasta-7,25-dien-3-ol. In comparison with respective control samples (leaf with no pest attack), the one attacked by red spider mite showed eighteen exclusive metabolites, whereas tea mosquito bug infested leaf showed six such exclusive metabolites.ConclusionsSome metabolites were found to be either increased or decreased in their amount in both the samples. The increased compounds were reported with insecticidal and pesticidal properties with respect to respective controls. Some metabolites were markers of pest attacks i.e. plant defense mechanism induced phytochemicals according to the literature as discussed in this research.

Effect of Methyl Jasmonate on the Performance of Tetranychus evansi Baker & Pritchard, 1960 (Acari: Tetranychidae) and Phytoseiulus longipes Evans, 1968 (Acari: Phytoseiidae) on Tomato Plants

Inducible anti-herbivore defenses in plants are predominantly regulated by jasmonic acid (JA). The red spider mite Tetranychus evansi Baker & Pritchard, 1960 (Acari: Tetranychidae) is an invasive pest known for its detrimental impact on tomato plants and other Solanaceae crops. Here, we investigated the extent to which T. evansi and the predatory mite Phytoseiulus longipes Evans, 1968 (Acari: Phytoseiidae) are affected by induced JA-defenses. Initially, we artificially induced the JA-response in tomato plants using exogenous methyl jasmonate (MeJA) and subsequently assessed the effect of JA defenses on spider mite by evaluating mortality and oviposition rates. Our findings revealed a higher mortality and lower oviposition rates on plants treated with MeJA compared to non-treated control plants. Furthermore, we examined the predatory mite's predation rates on spider mite eggs produced on MeJA-treated and non-treated tomato plants. The results showed a reduced predation on T. evansi eggs derived from MeJA-treated plants, indicating a potential negative impact of JA-induced defenses on the predator's performance. Finally, we released five predatory females on T. evansi-infested tomato plants treated and non-treated with MeJA, monitoring the predator population density for three generations. Predator population was not affected, as the abundance of larvae and adults was not significantly different between treatments. These findings underscore the negative impact of JA defenses on herbivores and highlight the trade-off it may pose on natural enemies.

Are predatory mites effective as biological control agents to suppress Oligonychus ilicis (Acari: Tetranychidae) in blueberry plantings?

Southern red mite, Oligonychus ilicis McGregor (Acari: Tetranychidae), is an important polyphagous spider mite pest that causes economic damage to many ornamentals, coffee, and fruit crops. Blueberry growers in the Southeastern United States, including Florida and Georgia, have experienced severe losses due to outbreaks of O. ilicis. Predatory mites are an important management tool used for controlling spider mites; however, predators have not been studied and successfully evaluated in blueberry systems. Amblyseius swirskii Athias-Henriot, Phytoseiulus persimilis Athias-Henriot, and Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) are among the most economically important arthropod agents used in augmentative biological control worldwide. To evaluate the potential of these 3 commercially available predatory mites for use in blueberry plantings, we conducted experiments under controlled laboratory conditions and in the greenhouse. In preliminary laboratory experiments, P. persimilis and N. californicus significantly reduced the number of O. ilicis motile stages below those found in the untreated control, indicating the potential for these 2 predatory mite species to suppress O. ilicis populations. Amblyseius swirskii did not perform well controlling O. ilicis motiles in the laboratory. Under greenhouse conditions, N. californicus and P. persimilis significantly reduced the number of eggs after 7 days of release and the number of motile stages after 14 days of release. This is the first report of using phytoseiid mites to suppress O. ilicis in blueberry systems in the United States. Further studies on predator behavior, feeding preferences, and acaricide compatibility with predators are required to investigate the possibility of using P. persimilis, and N. californicus as biological control agents of O. ilicis in blueberry systems.

Oligonychus perseae (Tetranychidae) Invasion in the Canary Islands: History, Management and Current Situation

Avocado production has boomed worldwide in recent years, and Spain, including the Canary Islands, has been no exception. The number of avocado growers in the region has increased significantly as growers recognize the potential of this crop. However, several species of spider mites (Tetranychidae) pose a risk to this crop, with the genus Oligonychus being the most diverse and having the greatest economic impact. In particular, Oligonychus perseae (Tuttle, Baker and Abbatiello) has been reported as the one mainly responsible for the economic damage in major avocado-producing regions worldwide. In this paper, we aim to present an overview of the studies conducted and the measures implemented to mitigate the impact of O. perseae after its arrival in the Canary Islands. Our objective is to provide a detailed description of the current status of this pest (O. perseae), with special attention to its situation 17 years after its first appearance in avocado crops in the Canary Islands. In doing so, we aim to provide valuable insights and knowledge to understand and manage better the challenges posed by O. perseae in this region.

Investigating biological performance, oviposition and diet preference of the twospotted spider mite feeding on various melon genotypes

The twospotted spider mite, Tetranychus urticae Koch, is one of the most dangerous pests for many crops worldwide, including the melon. Here, we raise the hypothesis that the resistance of melon genotypes to the spider mite is associated with the morphological characteristics of the leaves. We determined (i) the feeding preference and oviposition suitability of T. urticae on four melon genotypes, (ii) various biological parameters and population growth rate (ri) of T. urticae on different melon genotypes, (iii) the leaf morphology of the melon genotypes, and (iv) the relationship between the leaf characteristics and resistance to T. urticae. In no choice tests, lower numbers of adults and eggs of T. urticae were found in the genotypes CNPH 06–1047-343, CNPH 11–1071-43, and CNPH 06-1047-341 compared to control (Goldex). Individuals that fed on CNPH 06–1047-343, CNPH 06–1047-341, and CNPH 11–1071-43 genotypes had a longer egg incubation time, longer development time, lower immature viability, longer time to reach adult stage (egg–adult) and lower instantaneous rate of increase compared to control. These findings are in line with the fact that these three genotypes had thicker epidermis and greater mesophyll thickness than control genotype “Goldex”. Even the genotypes CNPH 06–1047-343, CNPH 06–1047-341, and CNPH 11–1071-43 had higher trichome densities, this morphological characteristic was not related with the resistance to T. urticae. CNPH 06–1047-343, CNPH 06–1047-341, and CNPH 11–1071-43 showed antibiosis and antixenosis against T. urticae and that resistance of the melon to T. urticae wss associated with the greater thickness of the leaf epidermis and mesophyll.

Ultrastructure of silk threads of the water spider Argyroneta aquatica (Clerck, 1757) (Araneae, Cybeidae) in comparison with that of some mites

Silk of the water spider Argyroneta aquatica (Clerck, 1757) was obtained in the laboratory in the form of a capturing web irrespective of the formation of a diving bell and egg cocoon. Silk threads were examined by light microscopy, scanning (SEM), and transmission electron microscopy (TEM) as well as by atomic force (AFM) microscopy. Based on the diameter and internal organization, the silk threads have been divided into five types—a-, b-, c-, d-, and e-types interlaced freely in the thread bundles taken for examinations. Threads of all types are infinitely long, non-branched, round in shape, uniform in width through their course, and rarely found to be ruptured. Threads of the a-type are mostly straight, up to 1,000 nm in diameter, and composed of a fibrillary wall enveloping an electron-dense vacuolated core, which may be occasionally absent. The wall may also become lost, leaving a single core substance surrounded by a slightly wrinkled double membrane. Threads of the b-, c-, and d-types are organized nearly identical, being composed of a fine granular electron-light uniform material enveloped by a fine membrane. The diameter of these threads varies from max. 500 nm in the b-type and 120 nm in the c-type to around 50 nm in the d-type. Threads of these types are more convoluted and more numerous than threads of the a-type. Threads of the last kind, the e-type, occur rarely and are significantly larger with a diameter of around 3.5–4.5 µm. They possess the layered membranous wall surrounding a uniformly dense core. The silk of the water mites Limnochares aquatica (L., 1758) and Limnesia maculata (O.F. Müller, 1776) is composed of threads of only one type that closely corresponded to the a-type threads of A. aquatica. Conversely, the silk of the two-spotted spider mite Tetranychus urticae (C.L. Koch, 1836) consists of threads highly correlated with the d-type threads of A. aquatica. This finding shows that in different phylogenetic lineages of arachnids, the mechanisms of silk production are quite similar.

Evaluation of chemical acaricides against the two-spotted spider mite, Tetranychus urticae (Koch) (Acari: Tetranychidae) in geothermal greenhouses in southern Tunisia

The two-spotted spider mite, Tetranychus urticae (Koch) (Acari: Tetranychidae), represents a major threat to geothermal greenhouses in southern Tunisia, causing considerable damage to geothermal crops. In this study, we evaluated the efficacy of new chemical acaricides against T. urticae infesting tomato crops under heated greenhouses: Cyflumetofen, Cinnamaldheyde, Fenazaquin, Pyridaben, Abamectin + Spinosad and Diafenthiuron. The results showed that all acaricides had a significant effect on the reduction of eggs and motile forms of T. urticae, although the reference treatment based on Diafenthiuron varied between 84.40% and 100%. In conclusion, this study highlights the efficacy of several acaricides in managing T. urticae populations, offering promising prospects for effective control of this mite in heated greenhouse crops.

Spider mite herbivory induces an abscisic acid-driven stomatal defense.

Arthropod herbivory poses a serious threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest two-spotted spider mite (Tetranychus urticae) inflicts rapid damage and remains challenging due to its broad target range. In this study, we explored the Arabidopsis (Arabidopsis thaliana) response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, and stomatal closure during water stress. Leveraging a FRET-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types post-mite feeding. While ABA's role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation alongside intact canonical biotic stress signaling, indicating an independent function of ABA in mite defense. We established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage through genetic and pharmacological interventions targeting ABA levels, ABA signaling, stomatal aperture, and density. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, reinforces the intricate relationship between these stress types.

Effect of Mammea americana Aqueous Extract on the Control of the Coffee Red Spider Mite

The coffee red spider mite, Oligonychus ilicis, stands out as one of the main pests of Conilon coffee. The use of synthetic chemical control has led to an increase in the population of this mite and a reduction in its natural enemies. Aiming to find viable alternatives, this study aimed to evaluate the acaricidal potential of “abricó” peel extract, Mammea americana, in the management of O. ilicis. Each treatment consisted of 7 repetitions, with 10 individuals per repetition. They were placed in Petri dishes (10.0 x 1.2 cm), containing coffee leaf disks (4 cm diameter) inside, and moistened cotton at the bottom of the dish and around the disks. The peels of M. americana were dried, crushed, and diluted in aqueous solution to obtain extracts at concentrations of 2; 2.57; 3.30; 4.24; 5.45; and 7 %. The application was done by spraying, using an Alfa 2 model airbrush connected to a compressor calibrated with a constant pressure of 1.3 psi. 1 mL of solution of each concentration was applied for each repetition. Distilled water and the surfactant Tween® 80 (0.05 % v/v) were used as control treatments. The acaricidal effect was evaluated 24, 48, and 72 hours after spraying, and the lethal concentrations LC50 and LC90 were calculated. The results of the toxicity tests indicated an increase in the mortality of O. ilicis with the increase in the concentrations of aqueous extracts of M. americana, resulting in 100 % mortality. The LC90 was estimated at 3.83 %. In the chemical analysis of the M. americana extract, the presence of phenolic acids, tannins, and flavonoids was observed at concentrations of 39.150, 40.783, and 0.0349 mg-1, respectively. We conclude that the aqueous extract of M. americana peels demonstrated acaricidal potential in a controlled environment for the coffee red spider mite.

Within-tree distribution and seasonal dynamics of Eutetranychus banksi and Euseius stipulatus (Acari: Tetranychidae, Phytoseiidae) on citrus: Implications for the biological control of the pest

The Texas citrus mite, Eutetranychus banksi (McGregor) (Acari: Tetranychidae), is a citrus pest widely distributed throughout the Americas and recently introduced in Spain. In this study we studied the within-tree distribution of E. banksi and the predatory phytoseiid mites, identify the phytoseiid species associated with the pest, and describe the seasonal trends to analyse the predator’s behaviour in response to the increase in pest density, allowing evaluation of biological control possibilities. The Texas citrus mite was mainly found on the adaxial (upper) side of leaves from the current year's shoots located at the periphery of the tree canopy, whereas phytoseiids prefer the abaxial (lower) side of leaves inside the tree canopy. The spider mite preferred to feed on leaves rather than fruits, whereas phytoseiids use both substrates equally. Eutetranychus banksi showed a single population peak in late summer-early autumn, while phytoseiids showed two peaks, a main spring peak and a second less abundant in autumn. The seasonal dynamics of E. banksi and phytoseiids on fruits occurred in parallel to those recorded on leaves. Euseius stipulatus (Athias-Henriot) was the most frequent and abundant phytoseiid species, apparently displacing other predatory mites. In autumn, when E. banksi reached high densities, phytoseiids moved from the leaf abaxial sides inside the tree canopy to the adaxial sides on the periphery and to the fruits, to feed on E. banksi. In addition, a change in phytoseiid colouration from white to reddish-brown was observed. Both, the number of red phytoseiids and their leaf occupation increased significantly in response to the prey population growth, which was indirect evidence of their contribution to the biological pest control. However, the low predator:prey ratios observed cannot avoid the pest population growth.

A chromosome-level genome assembly of the spider mite Tetranychus piercei McGregor

Despite the rapid advances in sequencing technology, limited genomic resources are currently available for phytophagous spider mites, which include many important agricultural pests. One of these pests is Tetranychus piercei (McGregor), a serious banana pest in East Asia exhibiting remarkable tolerance to high temperature. In this study, we assembled a high-quality genome of T. piercei using a combination of PacBio long reads and Illumina short reads sequencing. With the assistance of chromatin conformation capture technology, 99.9% of the contigs were anchored into three pseudochromosomes with a total size of 86.02 Mb. Repetitive elements, accounting for 14.16% of this genome (12.20 Mb), are predominantly composed of long-terminal repeats (30.7%). By combining evidence of ab initio prediction, transcripts, and homologous proteins, we annotated 11,881 protein-coding genes. Both the genome and proteins have high BUSCO completeness scores (>94%). This high-quality genome, along with reliable annotation, provides a valuable resource for investigating the high-temperature tolerance of this species and exploring the genomic basis that underlies the host range evolution of spider mites.

Automated imaging coupled with AI-powered analysis accelerates the assessment of plant resistance to Tetranychus urticae

The two-spotted spider mite (TSSM), Tetranychus urticae, is among the most destructive piercing-sucking herbivores, infesting more than 1100 plant species, including numerous greenhouse and open-field crops of significant economic importance. Its prolific fecundity and short life cycle contribute to the development of resistance to pesticides. However, effective resistance loci in plants are still unknown. To advance research on plant-mite interactions and identify genes contributing to plant immunity against TSSM, efficient methods are required to screen large, genetically diverse populations. In this study, we propose an analytical pipeline utilizing high-resolution imaging of infested leaves and an artificial intelligence-based computer program, MITESPOTTER, for the precise analysis of plant susceptibility. Our system accurately identifies and quantifies eggs, feces and damaged areas on leaves without expert intervention. Evaluation of 14 TSSM-infested Arabidopsis thaliana ecotypes originating from diverse global locations revealed significant variations in symptom quantity and distribution across leaf surfaces. This analytical pipeline can be adapted to various pest and host species, facilitating diverse experiments with large specimen numbers, including screening mutagenized plant populations or phenotyping polymorphic plant populations for genetic association studies. We anticipate that such methods will expedite the identification of loci crucial for breeding TSSM-resistant plants.

Early detection of infestation by mustard aphid, vegetable thrips and two-spotted spider mite in bok choy with deep neural network (DNN) classification model using hyperspectral imaging data

Although exclusion measures (e.g., air filters, biosecurity practices) can be employed to prevent occurrence of pest outbreaks, indoors vegetable farms in Singapore are still susceptible to various arthropod pests. Due to strong interest from the industry to pursue pesticide-free production, indoors pest management is often focused on early detection for timely containment and eradication, implying the importance of robust and vigorous pest monitoring programs. In recent years, application of machine vision technologies, especially hyperspectral imaging (HSI), has been studied for their capacity to early detect pest infestation. However, there is a lack of studies conducted in actual indoor environments and on multiple arthropod pests. Thus, this study aimed to non-destructively collect hyperspectral data of bok choy Brassica rapa subspecies chinensis which were healthy or infested with either mustard aphids Lipaphis erisymi, vegetable thrips Echinothrips americanus or two-spotted spider mites Tetranichus urticae in indoor environment to build deep neural network (DNN) classification model for early detection. Based on HSI data of control and infested plants collected daily over a period of two weeks, we found that point percentage change (PPC) values associated with leaf reflectance in 420–440 nm, 500–520 nm, 620–637 nm, 720–800 nm, and 850 nm were sensitive to infestation by the mentioned arthropod pests. Deep Neural Network (DNN) classification models trained on collected HSI data were found to outperform Linear Discriminant Analysis (LDA) and Support Vector Machine (SVM) classification models. DNN models achieved 92.8 ± 0.4 % overall classification accuracy across all days. As early as two days after infestation, DNN models could achieved classification precision values of 96.4 %, 96.9 %, 93.9 % and 100 % for control plants and plants infested with either aphids, spider mites or thrips respectively. These results highlight the feasibility of multiclass early detection of different arthropod pests and the potential of HSI system coupled with DNN classification as an autonomous plant health monitoring tool in indoor crop production.

Implementation of Ant Colony Optimization and Principal Component Analysis for Early Prediction of Tomato Leaf Diseases: A Feature Reduction Approach

This paper details the implementation of a sophisticated algorithmic framework designed for the early prediction of various tomato leaf diseases, crucial for enhancing crop management and yield. The research deploys image processing techniques to extract pivotal features such as Red Mean, Green Mean, Blue Mean, Height, Width, and Defect Color channels from high-resolution images of tomato leaves. These features serve as indicators for diseases including Bacterial Spot, Early Blight, Late Blight, Leaf Mold, Septoria Leaf Spot, and infestations by Two-spotted Spider Mites. The core of the implementation lies in the integration of Ant Colony Optimization (ACO) with Principal Component Analysis (PCA) for feature reduction, which streamlines the dataset while retaining critical information. This combination not only reduces computational load but also improves the accuracy of the early prediction model. The paper demonstrates the application of this hybrid approach and compares its performance with existing models, emphasizing its efficiency and accuracy in early-stage disease prediction. The findings indicate that the proposed method outperforms traditional techniques, offering a reliable and scalable solution for agricultural disease management.

The six-spotted spider mite, Eotetranychus sexmaculatus (Riley) (Trombidiformes: Tetranychidae) in Australia, New Zealand, Japan and USA: a revised morphological and molecular-based concept, synonyms, and related species

Based on morphological and molecular evidence, Eotetranychus asiaticus Ehara is confirmed as a junior synonym of E. sexmaculatus (Riley). Eotetranychus queenslandicus Manson differs to E. sexmaculatus in some morphological characters states, and currently there is insufficient evidence to confirm if it is also a junior synonym. We therefore propose that it remains a valid species until fresh material can be collected from the type host (Codiaeum variegatum (L.) A.Juss.; Euphorbiaceae) in the type location (Freshwater, Queensland, Australia) for molecular analysis and further comparisons. Eotetranychus sexmaculatus is confirmed as present in Australia and New Zealand. Our analyses indicate that specimens identified as E. sexmaculatus from avocado (Persea americana Mill.; Lauraceae) in Western Australia and New Zealand, and specimens of E. asiaticus from the type host (Ficus erecta Thunb.; Moraceae) and type location (Tomigusuku, Okinawa, Japan) are conspecific with specimens of E. sexmaculatus recently collected from the type host (Citrus sp.; Rutaceae) and type location (Florida, USA), with 0–3.6% divergence in a fragment (451 bp) of cytochrome oxidase subunit I (COI), and 0–0.3% in the ribosomal internal transcribed spacer II (ITS2) gene. Herein we redefine E. sexmaculatus, providing a revised diagnosis, notes on leg chaetotaxy, and variation in the shape of the aedeagus—which is a keystone feature critical for determining species boundaries of spider mite species that have males. Our findings also reinforce the potential of the eupathidion on the palptarsus suζ (i.e. the spinneret) for species diagnoses.

The development of an egg-soaking method for delivering dsRNAs into spider mites

Recently, the first sprayable RNAi biopesticide, Ledprona, against the Colorado potato beetle, Leptinotarsa decemlineata, has been registered at the United States Environmental Protection Agency. Spider mites (Acari: Tetranychidae), a group of destructive agricultural and horticultural pests, are notorious for rapid development of insecticide/acaricide resistance. The management options, on the other hand, are extremely limited. RNAi-based biopesticides offer a promising control alternative to address this emerging issue. In this study, we i) developed an egg-soaking dsRNA delivery method; ii) evaluated the factors influencing RNAi efficiency, and finally iii) investigated the potential mode of entry of this newly developed egg-soaking RNAi method. In comparison to other dsRNA delivery methods, egg-soaking method was the most efficient, convenient/practical, and cost-effective method for delivering dsRNAs into spider mites. RNAi efficiency of this RNAi method was affected by target genes, dsRNA concentration, developmental stages, and mite species. In general, the hawthorn spider mite, Amphitetranychus viennensis, is more sensitive to RNAi than the two-spotted spider mite, Tetranychus urticae, and both of them have dose-dependent RNAi effect. For different life stages, egg and larvae are the most sensitive life stages to dsRNAs. For different target genes, there is no apparent association between the suppression level and the resultant phenotype. Finally, we demonstrated that this egg-soaking RNAi method acts as both stomach and contact toxicity. Our combined results demonstrate the effectiveness of a topically applied dsRNA delivery method, and the potential of a spray induced gene silencing (SIGS) method as a control alternative for spider mites.

Microbiome changes in Akanthomyces attenuatus JEF-147-infected two-spotted spider mites

The two-spotted spider mite (Tetranychus urticae Koch) is an agriculturally serious polyphagous pest that has acquired strong resistance against acaricides because of its short life cycle and continuous exposure to acaricides. As an alternative, mite-pathogenic fungi with different modes of action could be used to control the mites. The spider mite has symbiotic microorganisms that could be involved in the physiological and ecological adaptations to biotic stresses. In this study, mite-pathogenic fungi were used to control female adults, and the microbiomes changes in the fungus-infected mites were analyzed. The acaricidal activity of 77 fungal isolates was tested, and Akanthomyces attenuatus JEF-147 exhibited the highest acaricidal activity. Subsequently a dose–response assay and morphological characterization was undertaken For microbiome analysis in female adults infected with A. attenuatus JEF-147, 16S rDNA and ITS1 were sequenced using Illumina Miseq. Infected mite showed a higher Shannon index in bacterial diversity but lower index in fungal diversity. In beta diversity using principal component analysis, JEF-147-treated mites were significantly different from non-treated controls in both bacteria and fungi. Particularly in bacterial abundance, arthropod defense-related Rickettsia increased, but arthropod reproduction-associated Wolbachia decreased. The change in major bacterial abundance in the infected mites could be explained by a trade-off between reproduction and immunity against the early stage of fungal attack. In fungal abundance, Akanthomyces showed up as expected. Foremost, this work reports microbiome changes in a fungus-infected mite and suggests a possible trade-off in mites against fungal pathogens. Future studies will focus on gene-based investigations related to this topic.

Conspecific cues mediate habitat selection and reproductive performance in a haplodiploid spider mite

Abstract Selection of a suitable habitat by animals before settlement is critical for their survival and reproduction. In silk spinning arthropods like spider mites, denser webs offer protection from predation and serve as a dispersal mode. Settling in habitats with the presence of conspecifics and silk webs can benefit the habitat-searching females. Silk and conspecifics usually coexist, but their distinct effects on female colonization have received little attention. In this study, we used a haplodiploid spider mite, Tetranychus ludeni Zacher (Acari: Tetranychidae), to examine the impact of conspecific cues, including cues from ovipositing conspecifics and silk, on habitat selection and subsequent reproductive performance of females. Results show that females significantly preferred habitats with cues from neighbouring conspecifics and silk, and neighbouring conspecifics induced additive effect to that of silk on habitat selection. Conspecific cues did not boost female reproduction but facilitated females laying larger eggs that were more likely to be fertilised and to develop to daughters. When given a choice between silk-covered and clean habitats, females preferred silk-covered habitat, laid a similar number of eggs with similar size, but produced more daughters, suggesting that T. ludeni females can adjust the size threshold for fertilization in response to the current social environment. Knowledge of this study improves our understanding of spider mite habitat selection and post-settlement reproductive performance behaviours.

Small‐scale dispersal and gene flow of the agricultural pest two‐spotted spider mite in apple orchards: Implication from landscape ecological and population genetic analyses

AbstractThe two‐spotted spider mite, Tetranychus urticae Koch (Acarina, Tetranychidae), is a notorious agricultural pest known for its high dispersal ability. Understanding the dispersal patterns of T. urticae is crucial for studying its population dynamics and assessing the risk of gene dispersal related to acaricide resistance. We investigated the impact of surrounding landscapes on T. urticae occurrence and detected gene flow between nearby apple orchards. Land use data within 0.2–2 km radius buffers of the orchards were extracted and summarized using principal component analysis. The effects of landscape composition on the occurrence of T. urticae in apple orchards were analyzed using a hierarchical Bayesian model that considers spatial autocorrelation. In addition, we conducted a population genetic analysis on samples collected from five orchards. The results indicate that the best model was one at a 200‐m scale, revealing a positive correlation between forest area ratio and T. urticae occurrence. The population genetic analysis demonstrated distinct genetic structures within T. urticae populations across different orchards. However, we estimated gene flow among some orchards that were geographically close. These findings suggest that T. urticae may migrate from surrounding landscapes, particularly forests, and nearby orchards to apple orchards. These findings have substantial implications for developing control units based on the gene flow range of the two‐spotted spider mite, as well as for assessing the risk of infestation in each orchard.