Tetranychus Urticae Research Articles

Development of BC3F2 Tomato Genotypes with Arthropod Resistance Introgressed from Solanum habrochaites var. hirsutum (PI127826)

Arthropod pests are among the biggest problems faced in tomato production worldwide. To overcome the losses caused by these pests, one of the most sustainable and economical strategies is the use of resistance introgressed from wild species. We aimed to develop BC3F2 tomato genotypes with high levels of zingiberene (ZGB) and resistance to whitefly (Bemisia tabaci biotype B), South American tomato pinworm (Tuta absoluta), and the two-spotted spider mite (Tatranychus urticae), from the wild accession of Solanum habrochaites var. hirsutum (accession PI127826). The quantification of ZGB in 520 BC3F2 genotypes and in the parentals yielded the selection of five genotypes with high ZGB content and three with low ZGB content, which were then infested with B. tabaci, T. absolute, and T. urticae. In these eight genotypes and in the parents, the types and amounts of trichomes on the leaves were determined. Additionally, molecular markers were used to identify the genotypes with a higher recurrent genome recovery. The results confirmed the transfer of resistance from S. habrochaites to the BC3F2 genotypes and showed that this resistance seems to be directly related to high concentrations of ZGB and the presence of type IV trichomes.

Molecular Mechanisms Underlying Metabolic Resistance to Cyflumetofen and Bifenthrin in Tetranychus urticae Koch on Cowpea.

Tetranychus urticae Koch (T. urticae) is one of the most tremendous herbivores due to its polyphagous characteristics, and is resistant to most acaricides. In this study, enzyme-linked immunosorbent assay (ELISA), transcriptome sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) were carried out to analyze the mechanisms of T. urticae metabolic resistance to cyflumetofen and bifenthrin on cowpea. The enzyme activity of UDP-glucuronosyltransferases (UGTs) and carboxylesterases (CarEs) in the cyflumetofen-resistant (R_cfm) strain significantly decreased, while that of cytochrome P450 monooxygenases (P450s) significantly increased. Meanwhile, the activities of glutathione-S-transferases (GSTs), CarEs and P450s in the bifenthrin-resistant (R_bft) strain were significantly higher than those in the susceptible strain (Lab_SS). According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, in the R_cfm mite strain, two carboxyl/cholinesterase (CCE) genes and two P450 genes were upregulated and one gene was downregulated, namely CYP392E7; in the R_bft mite strain, eleven CCE, nine UGT, two P450, four GST and three ABC genes were upregulated, while four CCE and three P450 genes were downregulated. Additionally, 94 differentially expressed genes (DEGs) were common to the two resistant groups. Specifically, TuCCE46 and TuCCE70 were upregulated in both resistant groups. Furthermore, the qRT-PCR validation data were consistent with those from the transcriptome sequencing analysis. Specifically, TuCCE46 (3.37-fold) was significantly upregulated in the R_cfm strain, while in the R_bft strain, TeturUGT22 (5.29-fold), teturUGT58p (1.74-fold), CYP392A11 (2.89-fold) and TuGSTd15 (5.12-fold) were significantly upregulated and TuCCE01 (0.13-fold) and CYP392A2p (0.07-fold) were significantly downregulated. Our study indicates that TuCCE46 might play the most important role in resistance to cyflumetofen, and TuCCE01, teturUGT58p, teturUGT22, CYP392A11, TuGSTd15, TuGSTm09 and TuABCG-13 were prominent in the resistance to bifenthrin. These findings provide further insight into the critical genes involved in the metabolic resistance of T. urticae to cyflumetofen and bifenthrin.

Design, Synthesis, and Bioactivity of Spiro Derivatives Containing a Pyridine Moiety.

We designed and synthesized a series of pyridine spiro derivatives and evaluated their insecticidal and antiviral activities. Some compounds exhibited good insecticidal and antiviral activities. Notably, the E series of compounds displayed good insecticidal activity against Tetranychus urticae. Compounds E20 (EC50 = 63.68 mg/L) and F4 (EC50 = 47.81 mg/L) exhibited inactivation activities against the tobacco mosaic virus (TMV), which were similar to that of Ningnanmycin (EC50 = 58.01 mg/L). Molecular docking showed that compounds E20 and F4 exhibited satisfactory affinities for the TMV coat protein (TMV-CP), with binding energies (-6.7 and -6.4 kcal/mol, respectively) slightly lower than that of Ningnanmycin (-6.3 kcal/mol). Further, molecular dynamics analysis revealed that compounds E20 and F4 exhibited better binding stability values than Ningnanmycin. Microscale thermophoresis showed that compounds E20 (Kd = 0.053 ± 0.016 μM) and F4 (Kd = 0.045 ± 0.022 μM) bound more strongly to TMV-CP than Ningnanmycin (Kd = 0.10 ± 0.029 μM). The results of transmission electron microscopy showed that these two compounds hindered the self-assembly and growth of TMV. In summary, we showed that these pyridine spiro derivatives could be used as a basis for the research and development of novel pesticides.

Identification of cassava germplasms resistant to two-spotted spider mite in China: From greenhouse large-scale screening to field validation.

Utilization of resistant germplasm is considered as an effective, economical and eco-friendly strategy for cassava pest management. Tetranychus urticae, known as the two-spotted spider mite (TSSM), is a devastating pest in Asian cassava planting countries as well as in China. However, the resistant levels of abundant cassava germplasms to TSSM remains largely unknown. To fill this knowledge gap, we conducted screening of 202 cassava germplasm for resistance to TSSM in China based on the classification of mite damage phenotype, under both greenhouse and field conditions. The three rounds of large-scale greenhouse experiments had identified two highly resistant (HR) varieties (C1115 and MIANDIAN), five resistant (R) varieties (SC5, SC9, SC15, COLUMBIA-4D and LIMIN) and five highly susceptible (HS) varieties (KU50, BREAD, SC205, TMS60444 and BRA900), besides, these 'HR' and 'R' varieties would significantly repress the normal development and reproduction of TSSM. In addition, the 12 cassava varieties selected from the greenhouse screening were further subjected to consecutive five years of field validation at Danzhou, Wuming and Baoshan. The seven resistant varieties not only exhibited stable TSSM-resistance performance across the three field environments, but also possessed the same resistant levels as the greenhouse identification, while the resistant varieties SC5 was an exception, which was identified as moderate resistant in Baoshan, indicating the variety-environment interaction may affect its resistance. Furthermore, regional yield estimation suggested that the higher the resistance level was, the better capacity in reducing the yield losses. This study demonstrated that the TSSM-resistant varieties could be considered as ideal materials in mite control or in future breeding programme of mite-resistant cassava plant.

Opposite roles of MAPKKK17 and MAPKKK21 against Tetranychus urticae in Arabidopsis.

After recognizing a biotic stress, plants activate signalling pathways to fight against the attack. Typically, these signalling pathways involve the activation of phosphorylation cascades mediated by Mitogen-Activated Protein Kinases (MAPKs). In the Arabidopsis thaliana-Tetranychus urticae plant-herbivore model, several Arabidopsis MAP kinases are induced by the mite attack. In this study, we demonstrate the participation of the MEKK-like kinases MAPKKK17 and MAPKKK21. Leaf damage caused by the mite was assessed using T-DNA insertion lines. Differential levels of damage were found when the expression of MAPKKK17 was increased or reduced. In contrast, reduced expression of MAPKKK21 resulted in less damage caused by the mite. Whereas the expression of several genes associated with hormonal responses did not suffer significant variations in the T-DNA insertion lines, the expression of one of these kinases depends on the expression of the other one. In addition, MAPKKK17 and MAPKKK21 are coexpressed with different sets of genes and encode proteins with low similarity in the C-terminal region. Overall, our results demonstrate that MAPKKK17 and MAPKKK21 have opposite roles. MAPKKK17 and MAPKKK21 act as positive and negative regulators, respectively, on the plant response. The induction of MAPKKK17 and MAPKKK21 after mite infestation would be integrated into the bulk of signalling pathways activated to balance the response of the plant to a biotic stress.

Biological Performance of Tetranychus bastosi (Acari: Tetranychidae) on different hosts

Tetranychus bastosi Tuttle, Baker and Sales (Acari: Tetranychidae) has been observed in more than 36 host species and it is considered a potential pest mite for several crops, however its occurrence is still restricted to Brazil. The present study determined the biological, reproductive parameters and host preference of T. bastosi in three plant species: Morus rubra L. (Moraceae); Ipomoea batatas L. (Convolvulaceae); and Psidium guajava L. (Myrtaceae). The incubation period of T. bastosi eggs was longer in M. rubra (5.9 days), followed by I. batatas and P. guajava (4.0 days for both). The longest larval period was observed in P. guajava (5.7 days). The longest durations of the protonymph and deutonymph stages were recorded in P. guajava (3 days) and M. rubra (2.3 days). However, T. bastosi could not complete its life cicle on P. guajava. The longest period from egg to adult of T. bastosi was observed in I. batatas (30 days). The highest longevity of T. bastosi was observed in the hosts I. batatas and M. rubra (39.8 and 30.2 days, respectively). The longest average duration of a generation (T) was observed on M. rubra 21.3 days. Nevertheless, for the intrinsic capacity for population increase (rm) and finite rate of increase (λ) no differences were observed on I. batatas and M. rubra. In this sense, T. bastosi presents a high biological performance in I. batatas and M. rubra, however P. guajava was not considered a suitable host for the red spider mite.

The Essential Oil from the Resurrection Plant Myrothamnus moschatus Is Effective against Arthropods of Agricultural and Medical Interest.

This work aimed to evaluate the chemical composition, insecticidal and acaricidal potential of the essential oil (EO) obtained from the resurrection plant Myrothamnus moschatus (Baill.) Baill. (Myrothamnaceae) from Madagascar. The EO bioactivity was evaluated against selected arthropod pests and vectors of agricultural and public health relevance. The most abundant volatile compounds were trans-pinocarveol (37.7 ± 4.2%) and pinocarvone (20.8 ± 3.1%), similar to the EO of the chemotype collected from the same region. Lethal concentrations (LC50) or doses (LD50) from acute toxicity tests were estimated for Musca domestica (L.) adults at 22.7 µg adult-1, for Spodoptera littoralis (Boisduval) larvae at 35.6 µg larva-1, for Culex quinquefasciatus (Say) at 43.6 µg mL-1, for adults of Metopolophium dirhodum (Walker) at 2.4 mL L-1, and for adults of Tetranychus urticae (Koch) at 1.2 mL L-1. The good insecticidal and acaricidal activities determined in this work may open a new perspective on the use of this plant as a source of botanical insecticide ingredients. The exploitation of this species could also be important for the African economy, helping local farmers cultivating this plant.

Fused Pyrroles in Cholestane and Norcholestane Side Chains: Acaricidal and Plant Growth-Promoting Effects

Herein, we describe the synthesis and characterization of fused pyrroles in cholestane and norcholestane side chains derived from kryptogenin and diosgenin, respectively. Both conventional and microwave heating techniques were used to synthesize the steroidal pyrroles from primary amines, with the microwave method producing the highest yields. In particular, the norcholestane pyrroles were tested as acaricides against the two-spotted spider mite (Tetranychus urticae Koch) under laboratory conditions and as plant growth promoters on habanero pepper (Capsicum chinense Jacq) under greenhouse conditions.

Evaluation of the Acaricidal Activity of Lithium Chloride against Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae is a severe threat and a major source of yield loss in some agricultural and horticultural crops and it is also as a vector for several viruses. The number of active substances used against the pest is limited. Therefore, there is a continuous need for new active substances. Recently, lithium salts have been shown to be one of the most promising potential alternatives to control Varroa destructor; an apicultural mite pest. Based on this, we aimed to test whether the efficacy of lithium chloride extends to other agricultural mite pests, such as the two-spotted spider mite. In the present pilot study, we report for the first time that the efficacy of lithium chloride is extended to the two-spotted spider mite. Additionally, this is the first report on the acaricidal effectiveness of lithium on a plant mite pest. In the present study, we report three different concentrations that bear 100% mortality at concentrations of 5.52 M, 2.76 M, and 1.38 M. The symptoms caused were similar and followed the same sequence compared to those observed on animal parasites such as V. destructor and Dermanyssus gallinae.

Otanical insecticides for pest management in tomato grown in cultivation facilities

Abstract. An alternative to synthetic insecticides is the use of naturally occurring products, such as botanical products with insecticidal properties. Biological testing of the botanical products Krisant EC 750 ml/ha and Neem Azal T/S 0.3% was performed at the Maritza Vegetable Crops Research Institute – Plovdiv to determine their effectiveness against potato aphid (Macrosiphum euphorbiae Thomas, 1878), thrips (Thrips tabaci Lindemanla, 1889; Frankliniella occidentalis Pergande, 1895), greenhouse whitefly (Trialeurodes vaporariorum Westwood, 1856), cotton bollworm (Helicoverpa armigera Hübner, 1808), tomato leaf miner (Tuta absoluta Meyrick, 1917) and two-spotted spider mite (Tetranychus urticae Koch, 1836). These species are some of the most common economically important pests in growing tomatoes in greenhouses. The phytopesticides Neem Azal T/S and Krisant EC were applied alone and in combination. The tested plant protection products showed very good biological activity against these pests and relatively higher effectiveness over 78% shows the combined treatment.

Strawberry Cultivar Evaluation for Fall-planted High Tunnel System

Locally produced strawberries (Fragaria ×ananassa) have outstanding market potential. But strawberry production has been decreasing in the north-central United States, partly because of high production risks associated with the traditional matted-row system. The annual plasticulture system attracts attention but its low yield limits the wide adoption of the production system in the north-central United States. High tunnels are widely used to extend strawberry seasons worldwide, but the system was not fully explored in the United States. Although the benefits of growing strawberries in high tunnels were recognized, information on suitable strawberry cultivars specific for the fall-planted high tunnel production system is limited. A wide range of short-day and day-neutral strawberry cultivars, including recently released cultivars, were evaluated in the fall-planted annual plasticulture high tunnel systems for three seasons. Averaged among cultivars, the marketable yields were 1.96, 1.35, and 2.27 lb/plant for 2015–16, 2019–20, and 2020–21 seasons, respectively. The combined use of high tunnels and floating rowcovers created favorable microclimate conditions that led to high yields. Florida Radiance, San Andreas, Chandler, and Rocco were the top-yielding cultivars. Besides Chandler, the other top-yielding cultivars entered peak harvest in the second half of April. Harvests ended at the end of May or early June. All cultivars reached the US Department of Agriculture standard for total soluble solids in all three seasons, although Camino Real, FL Radiance, and Sweet Sensation consistently had relatively lower sugar content. Considering a warm-season crop could grow in high tunnels before or after strawberry, a diversified cropping system involving strawberry and other vegetables is highly valuable for high tunnel production systems in the north-central United States. This study did not compare cultivars’ resistance to diseases, but it should be a critical factor in selecting cultivars. Future studies are also warranted to evaluate the effects of incorporating soil treatments and cover cropping for suppressing diseases in the soil-based high tunnel system. Sustainable management strategies to control two-spotted spider mites (Tetranychus urticae) are also crucial in successfully using the system in the north-central United States.

RNA interference machinery in the two-spotted spider mite, Tetranychus urticae Koch

RNA interference (RNAi) or post-transcriptional gene silencing is a biological process conserved in a broad range of eukaryotes and triggered by endogenous or exogenous double-stranded RNA (dsRNA). RNAi suppresses the endogenous expression of the target gene of which the mRNA sequence is complementary to the dsRNA sequence. RNAi has been widely used as a gene functional analysis technology, and recently, exogenous dsRNA has begun to be applied to a sprayable biopesticide with a different mode-of-action from conventional synthetic pesticides. The two-spotted spider mite, Tetranychus urticae Koch (Trombidiformes: Tetranychidae), is distributed worldwide and has been known as one of the most difficult agricultural pests to control due to its rapid development of resistance to synthetic pesticides. Therefore, the development of RNAi-based biopesticide targeting this species is highly anticipated. However, the function of RNAi machinery in this species remains unclear. Processing dsRNA into small RNA is a fundamental process contributing to RNAi efficacy. Here we performed functional analysis of TuDcr1 and TuDcr2 genes, homologues of Drosophila melanogaster Dicer-1 and Dicer-2, which belong to the RNase III family. The nucleotide sequences of TuDcr1 (tetur19g00520), TuDcr2 (tetur07g00990), and an intergenic region as a negative control (NC) were obtained from the ORCAE database and used for PCR amplification of each DNA fragment. RNA synthesized by in vitro transcription from each DNA fragment was used to prepare dsRNA specific to TuDcr1, TuDcr2, and NC (dsRNA-TuDcr1, dsRNA-TuDcr2, and dsRNA-NC, respectively). A nylon-mesh-based feeding device was used to orally deliver dsRNA to age-synchronized adult female mites for 24 h. Both TuDcr1 and TuDcr2 were upregulated after oral administration of dsRNA-NC, which indicates the activation of RNAi machinery by orally-delivered dsRNA. Downregulations of TuDcr1 and TuDcr2 were observed in mites fed on dsRNA-TuDcr1 and dsRNA-TuDcr2 when compared to dsRNA-NC. However, no significant effects were observed in the susceptibility to RNAi targeting an essential gene Vacuolar-type H+-ATPase after oral administration of dsRNA-TuDcr1, dsRNA-TuDcr2, or dsRNA-NC. The dsRNA-cleaving assay revealed that the dicing activity was reduced in mites fed on dsRNA-TuDcr1 and dsRNA-TuDcr2 when compared with dsRNA-NC and that the activity seemed to be higher in TuDcr2 than TuDcr1. Our results suggest that TuDcr1 and TuDcr2 possess the activity of dsRNA cleavage and that TuDcr2 is responsible for dicing exogenous dsRNA.

Adaptation mechanism of a spider mite population to tea plants

In herbivores, adaptation to different plants often occurs during their ecological speciation. Plants have a variety of defensive systems, especially toxic and repellent secondary metabolites, to cope with herbivore attacks, while herbivores often enhance their xenobiotic metabolism for detoxifying the defensive compounds. Once a population acquires the adaptation ability to plant defense, it will occupy the plant as a host. This reduces interaction with other populations even within the same species, causing the population to diverge, and consequently, reproductive isolation occurs. The Kanzawa spider mite (KSM), Tetranychus kanzawai Kishida (Trombidiformes: Tetranychidae), is a polyphagous arthropod that causes serious economic damage to agricultural and horticultural crops. KSM is an important pest of tea plants, Camellia sinensis (L.) Kuntze. There are adapted and non-adapted KSM populations to tea plants (adapted and non-adapted KSM). Both populations may have undergone ecological speciation through the interaction with tea plants. However, the mechanism underlying the differences between two KSM populations remains unclarified. The two-spotted spider mite (TSSM), Tetranychus urticae Koch (Trombidiformes: Tetranychidae), is closely related to KSM. Based on the highly-annotated TSSM genome sequence, we conducted comparative transcriptome and proteome analyses among adapted and non-adapted KSM, and TSSM on tea plants and the preferable host bean plants. Xenobiotic-metabolizing enzymes containing catechol dioxygenase, carboxylesterase, ABC transporter, Cathepsin L, and UDP-glycosyltransferase were upregulated in adapted KSM on tea plants. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that pathways related to oxidoreductase activity were particularly enriched in adapted KSM on tea plants. These enzymes should be dealing with catechins which are known as secondary metabolites of tea plants and to be toxic to spider mites. The survival rate in adapted KSM on tea plants was significantly reduced by RNAi targeting the gene encoding a catechol dioxygenase (TkCTD). These results suggest that TkCTD-mediated detoxification is involved in the adaptation of KSM to tea plants.

Roles of salivary proteins in bacteria-mediated reproductive manipulation in spider mites

Arthropods host a diverse range of microbes. Some symbiotic bacteria are important in influencing the performance of arthropods, especially when facing biotic and abiotic challenges. The symbiont Wolbachia is a genus of intracellular bacteria (Rickettsiaceae) found in about 40% of terrestrial arthropods. It causes a variety of reproductive alterations in arthropod hosts, such as inducing parthenogenesis, killing males, feminizing genetic males, and inducing cytoplasmic incompatibility (CI), and is well known as a reproductive manipulator in arthropods. Recent studies show that Wolbachia can also affect host fitness by mediating interactions between plant and herbivores. But it remains unclear whether saliva proteins are involved in this process. The two-spotted spider mite (Tetranychus urticae), a notorious cosmopolitan agricultural pest, harbors Wolbachia (Xie et al., 2006). In this study, we explored the effects of Wolbachia on biological performance of T. urticae (Bing et al., 2022). We showed that the Wolbachia-infected T. urticae decreased the number of deposited eggs but increased the egg hatching rate compared with Wolbachia-uninfected mites. With transcriptomic analysis data, we further demonstrated that Wolbachia infection upregulated the gene expression levels of many T. urticae salivary proteins, which include a cluster of Tetranychidae-specific, functionally uncharacterized SHOT1s (secreted host-responsive proteins of Tetranychidae). These SHOT1 genes were highly enriched in the proterosomas (Jonckheere et al., 2018) and were expressed more in the feeding stages (nymphs and adults) of mites than in eggs. RNAi experiments showed that knocking down SHOT1s could significantly decrease Wolbachia titer, increase the number of deposited eggs and decrease the egg hatching rate. Altogether, our results suggest that host salivary proteins are related to Wolbachia-mediated manipulations of host reproduction.

Molecular gut-content analysis in phytoseiid mites

Molecular gut content analysis has been used widely to elucidate predator-prey interaction both in natural and agricultural ecosystems. The two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae), is one of the most important pest species worldwide, mainly due to their acaricide resistance. In greenhouses, commercially available biological control agents (BCAs), such as Phytoseiiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae), have been used. However, in open fields like orchards, conservation biological control (CBC) is desirable rather than augmentation, because natural populations of phytoseiid mites, which can potentially control spider mites, are distributed. There can be several species of phytoseiid mites feeding on spider mites in the same habitat, and therefore it is important to know which species can control spider mites effectively. To this end, Hinomoto (2017) elucidated the effectiveness of molecular gut-content analysis in the predatory mite, N. californicus, and showed that ordinary agarose gel electrophoresis of PCR products could not detect any bands, but fluorescent-labeled primers successfully detected the gut contents of phytoseiid mites and confirmed they were derived from spider mite eggs. Furthermore, he also found that newly deposited spider mite eggs (less than 3 hr of oviposition) consumed by the predatory mites could not be detected even if fluorescent-labeled primers were used. To apply this technique in the fields, this should be carefully taken in the consideration, although it is unknown whether old or new eggs of spider mites are preferred. Regardless of this phenomenon, a combination of barcoding of phytoseiid mite species and molecular cut-content analysis will reveal real predator-prey food web in fields.

Prey stage preference and functional response of Neoseiulus striatus (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite, Tetranychus urticae, is one of the most serious phytophagous mites affecting maize in China. Recently, a species of predatory mite, Neoseiulus striatus Wu (Acari: Phytoseiidae), was found on maize plants in Inner Mongolia. To understand the potential of N. striatus as a biocontrol agent agsinst T. urticae, prey stage preference of N. striatus for T. urticae and functional response of N. striatus to T. urticae were explored in a climate chamber set at 25 ± 1 °C, 60 ± 5% RH, and a 16:8 h (L:D) photoperiod. The immature stages (eggs, larvae and nymphs) of T. urticae were used to avoid the influence of oviposition of female adults on the experimental results. In the no-choice experiment, N. striatus consumed significantly more larvae than on the other prey stages of T. urticae. At same time, in the choice experiment, N. striatus also significantly preferred larvae, followed by eggs and then nymphs of T. urticae. Neoseiulus striatus displayed a type II functional response on all immature stages of T. urticae. The number of prey consumed by N. striatus increased with the increase in prey density. In contrast, the predation rate of N. striatus decreased with increasing prey density, indicating that the proportions of prey consumed by N. striatus were higher at lower prey densities. Meanwhile, the highest attack rate of N. striatus was recorded when it fed on larvae of T. urticae, whereas the shortest handling time of N. striatus was recorded when it fed on eggs of T. urticae. In conclusion, N. striatus appears to be a promising natural enemy against T. urticae, especially at low prey densities. Thus, releasing N. striatus at the early occurrence of T. urticae may be an efficient method for suppressing the population of T. urticae and prevent their establishment on maize.

Efficacy of biorationals against the two-spotted spider mite infesting cucumber cultivated under net house

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is one of the key pests in cucumber cultivation, especially under protected conditions. The net houses and poly-net houses provide favourable environment for the multiplication of spider mite populations. The active stages of T. urticae suck cells sap which produces yellowish-white specklings on leaves and in severe infestations on the fruits. To promote non-chemical approach for mite management, studies on the efficacy of biorationals against T. urticae on net house cucumber were undertaken at Ludhiana, India. Cucumber variety Punjab kheera-1 was transplanted in February, 2021 and the crop was raised as per university recommended cultural and management practices for production of cucumber. The trial was conducted in a double-door, naturally ventilated net house structure made of galvanized iron pipes covered with ultraviolet stabilized 40 mesh size net and an arc-shaped dome. The trial was laid out in randomized block design with each of the concentration of the biorationals as one treatment with three replications each for all the treatments. The maximum and minimum temperature varied from 31oC to 36oC and 16oC to 18oC, respectively, while morning and evening relative humidity varied from 68 to 82% and 20 to 26 %, respectively during this period. There were 10 plants per plot in each treatment, separated by a distance of 50cm between 2 plots to avoid chemical interference owing to drift to adjacent treatments. For foliar applications of different treatments, a battery-operated knapsack sprayer fitted with hollow cone nozzle (40 PSI pressure) was used. Different biorationals including indigeneous ‘gurukul’ products as given in Palekar’s model of organic farming i.e. brahamastra (20 litres cow urine, 2 kg each of neem, mango, guava, castor leaves boiled in 100 litres of water and then filtered), neemastra (5 litres cow urine, 2 kg cow dung, 5 kg neem leaves boiled in 100 litres of water and then filtered), agniastra (20 litres cow urine, 5 kg neem leaves, 500g each of chilli and garlic fruits boiled in 100 litres of water and then filtered), all at the dose of 10, 20 and 30 ml/litre and botanicals viz. PAU homemade neem (Azadirachta indica) extract (PAUHMNE) @ 12, 14, 16 ml/litre, dried neem fruit powder extract (DNFPE) @ 3, 4, and 5%, PAU homemade dharek (Melia azaderach) extract (PAUHMDE) @ 12, 14, 16 ml/litre, dried dharek fruit powder extract (DDFPE) @ 3, 4 and 5%, and water spray along with untreated control were evaluated. The different indigenous products and botanicals were prepared freshly. Two sprays of the treatments were given at weekly interval, with the first spray at the appearance of 20–25 % mite infestation on plants. Observations were recorded from randomly selected three leaves each from top, middle and bottom canopies. The number of active stages of mites were recorded before the treatment, 1, 3, 5 and 7 days after each spray (DASI and DASII). The data were subjected to square root transformation and analyzed statistically following Analysis of Variance. The results were interpreted at 5 per cent level of significance using Tukey’s test. The number of mites before treatment ranged from 31.00 to 36.67 mites/ 2 cm leaf area in different treatments. Significantly lower mean number of mites was observed in agniastra (9.78), PAU HMDE (9.67), neemastra (10.67), DNFPE (11.47), DDFPE (12.22), brahamastra (12.67) and PAU HNE (13.11) at highest doses after 3 DASI and 5 DASI, compared to the untreated control (35.66 and 36.22). After the second spray of the biorationals, mean number of mites in PAU HNE (14.33), neemastra (14.67), PAU HMDE (15.17), DNFPE (15.33), DDFPE (16.17), agniastra (16.50), brahamastra (18.83) were observed at highest doses after 3 DASII and 5 DASII. No phytotoxicity was observed in any treatment. Seeing the overall results, it can be concluded that these botanicals and indigenous products can be incorporated in integrated mite management programme which will help in reducing the pesticide load and promoting organic cultivation of the vegetable crops. 

Status of abamectin resistance and mechanisms in Tetranychus urticae in China

The two-spotted spider mite, Tetranychus urticae Koch, is an important agricultural pest worldwide. It is prone to evolve resistance to pesticides, including organophosphates, pyrethroids, and some newly developed compounds (Xu et al., 2018; Alpkent et al., 2020), due to the frequent pesticide spray and the biological characteristics of T. urticae, such as short life cycle and parthenogenesis, etc. There is no doubt that the development of pesticide resistance and unclear resistant mechanisms have impeded the chemical control and resistance management of T. urticae in the field.

Effects of factitious prey on the biology and growth rate of the predatory mites Neoseiulus californicus (McGregor) (Acari: Phytoseiidae)

Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is being used on a commercial scale to control Tetranychus urticae Koch in open fields and greenhouses (Schausberger and Walzer 2001; Sato et al. 2007; Rezaie et al. 2017). To reduce the cost of rearing, phytoseiid mites are often cultured using factitious prey. To find out the most suitable factitious prey species for rearing N. californicus in this study, the development and reproduction of the predatory mite were assessed when fed on four factitious prey species: Carpoglyphus lactis, Lepidoglyphus destructor, Tyrophagus putrescentiae, Rhizoglyphus robini and the natural prey Tetranychus urticae (control). The results showed that N. californicus could survival on all prey species, however, their populations could increase when fed on C. lactis, L. destructor, and T. urticae. The life cycles of N. californicus fed on C. lactis and L. destructor (5.13 and 5.17 days respectively) were significantly shorter than those fed on T. urticae (5.89 days). The total number of eggs per female N. californicus fed on L. destructor was the highest (51.48 eggs/female), intermediate on T. urticae (45.11 eggs/female) and the lowest on C. lactis (38.68 eggs/female). When fed on L. destructor and T. urticae, the sex ratios (% female) in the 2nd generation of N. californicus reached approx. 70%—significantly higher than those predators fed on C. lactis (58.65%). The intrinsic rate of increase of N. californicus fed on L. destructor (0.338) was significantly higher than those females fed on C. lactis (0.304) and T. urticae (0.314). In conclusion, the factitious prey L. destructor is the best food source for mass rearing the predatory mite N. californicus.

Identification and profiling of Panonychus citri microRNAs and their potential function in regulating egg hatching and adult eclosion*

MicroRNA-mediated post-transcriptional regulations are involved in many physiological processes in insects, such as development, reproduction, metamorphosis, immunity, and insecticide resistance. In this study, the transcript profile of miRNAs over the developmental transitions of the citrus red mite Panonychus citri (McGregor) including egg hatching and three molting processes from egg to adult were analyzed. A total of 142 miRNAs, including 74 known, 64 novel miRNAs, 14 isomiRNAs and 12 duplicate miRNAs, were identified. Meanwhile, 21 differentially expressed miRNAs (DEMs) over the developmental transitions were analyzed, including 14 and 8 DEMs in egg hatching and molting process from mite deutonymph to adult. Amongst these DEMs, there were 2 and 2 in the developmental transitions from larva to protonymph and the protonymph to deutonymph, respectively, suggesting a complicated role of miRNAs in the regulation of developmental transitions. Additionally, two miRNAs were identified as reference miRNAs for mites from 7 candidate reference miRNAs after a systematic evaluation about their relative expression patterns at different developmental stages of both Panonychus citri and Tetranychus urticae. Furthermore, feeding miR-34-5p mimic in the deutonymph of P. citri resulted in a significant decrease in adult eclosion rate, and miR-92c and miR-305-5p also had similar functions in the emergence process from deutonymph to adult. Moreover, over expression of miR-315 and let-7a significantly inhibited egg hatching by dripping miRNA mimic on the back of mites with a microinjector. This study identified critical miRNAs involved in the developmental transitions of this important agricultural pest P. citri from egg hatching to adult eclosion, and thus provided a useful resource for exploring the application of miRNAs in mite pest control.