Tetranychus Urticae Research Articles

Using predatory species and entomopathogenic fungi as alternatives to chemical pesticides in green bean field

BackgroundGreen bean, Phaseolus vulgaris L. (Fam.: Leguminosae) is a widely consumed grain legume prized for its edible seeds and pods. It is susceptible to infestations with various pests as insects and mites throughout the growing season. In this study, the efficacy of the predatory species, Chrysoperla carnea (Stephens), Phytoseiulus persimilis Athias-Henriot and the entomopathogenic fungus (EPF) Metarhizium anisopliae (Hypocreales: Clavicipitaceae), as well as conventional pesticides, Mospilan and Vertimec, were evaluated against the most important pests, mainly the whitefly, Bemisia tabaci (Genn.) and the two-spotted spider mite, Tetranychus urticae Koch, infesting the green beans cultivated at two locations Giza and El-Menoufia Governorates in Egypt.ResultsThe findings demonstrate that treatments using C. carnea and M. anisopliae effectively reduced the whitefly population, while pesticide treatments were comparatively less effective. In the Giza plots, at the end of the experiments, the use of both M. anisopliae and C. carnea showed high reductions in whitefly population (85.57 and 84.87%), respectively, while in El-Menoufia, C. carnea (97.74%) was the most effective treatment followed by M. anisopliae (90.32%). Pesticide treatment in this case yielded a reduction rate of (22.76 and 59.67%) in Giza and El-Menoufia plots, respectively. However, for spider mite control, P. persimilis proved to be the most effective treatment in Giza and El-Menoufia plots, reducing the spider mite population to 98.44 and 96.14%, respectively. Metarhizium anisopliae treatment also displayed moderate effectiveness, with reduction rates of 75.62 and 75.37% in Giza and El-Menoufia plots, respectively. In comparison, pesticide treatment showed low effectiveness, with reduction rates of only 23.92 and 53.16% in the two locations, respectively.ConclusionApplications of the predator, C. carnea and the EPF, M. anisopliae were highly effective in reducing the population of whitefly, while the predator mite P. persimilis proved to be the most effective for controlling the spider mites. Overall, the study suggests that biocontrol agents, such as the predators and the EPF, can be considered as alternatives to synthetic chemical pesticides for controlling pests infesting green beans.

QTL analysis on a lemon population provides novel insights on the genetic regulation of the tolerance to the two-spotted spider mite attack

BackgroundAmong the Citrus species, lemon (Citrus limon Burm f.) is one of the most affected by the two-spotted spider mite (Tetranychus urticae Koch). Moreover, chemical control is hampered by the mite’s ability to develop genetic resistance against acaricides. In this context, the identification of the genetic basis of the host resistance could represent a sustainable strategy for spider mite control. In the present study, a marker-trait association analysis was performed on a lemon population employing an association mapping approach. An inter-specific full-sib population composed of 109 accessions was phenotyped through a detached-leaf assays performed in modified Huffaker cells. Those individuals, complemented with two inter-specific segregating populations, were genotyped using a target-sequencing approach called SPET (Single Primer Enrichment Technology), the resulting SNPs were employed for the generation of an integrated genetic map.ResultsThe percentage of damaged area in the full-sib population showed a quantitative distribution with values ranging from 0.36 to 9.67%. A total of 47,298 SNPs were selected for an association mapping study and a significant marker linked with resistance to spider mite was detected on linkage group 5. In silico gene annotation of the QTL interval enabled the detection of 13 genes involved in immune response to biotic and abiotic stress. Gene expression analysis showed an over expression of the gene encoding for the ethylene-responsive transcription factor ERF098-like, already characterized in Arabidopsis and in rice for its involvement in defense response.ConclusionThe identification of a molecular marker linked to the resistance to spider mite attack can pave the way for the development of marker-assisted breeding plan for the development of novel selection coupling favorable agronomical traits (e.g. fruit quality, yield) with a higher resistance toward the mite.

To move or not to move: Dispersal of Orius insidiosus in strawberry plants

AbstractSpatial and temporal distribution of food resources influences predatory insects' foraging and dispersal behavior. Orius insidiosus (Say) (Hemiptera: Anthocoridae) is a good biological control agent of western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in the strawberry crop and consumes two‐spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae), and pollen as well. Augmentative biological control programs may fail if, following release, predators disperse from the crop. We studied the dispersal of O. insidiosus as a function of pollen availability, density of their main prey WFT, and the presence of the alternative prey TSSM, within and between strawberry plants. We found that O. insidiosus remained on the flowers during the 24 h of the assay. The dispersal of predators to a neighboring flower with thrips was approximately six times greater from a flower without pollen than from a flower with pollen. When TSSM was the only prey available, O. insidiosus colonized the leaves, and its dispersal within the plant was greater. At the plot scale, the predator dispersal from the release plant to other plants also depended on the presence of flowering plants and prey. Our results highlight the importance of flowering plants and pollen availability in enhancing the persistence of O. insidiosus in strawberry plants. Releases of this predator in the strawberry crop should be after the beginning of flowering, even at low WFT densities.

Phytochemical investigation and evaluation of acaricidal activity of Ammi crinitum Guss. Against the two-spotted spider mite Tetranychus urticae Koch

Ammi crinitum Guss., a species belonging to the Apiaceae family, is an exclusive and endemic plant of the Sicily region, Italy. Considering the limited scientific attention given to A. crinitum, herein, for the first time, metabolite profiles of polar extracts (MeOH) of the aerial parts, flowers, and roots were investigated by liquid chromatography coupled to electrospray ionization and high resolution multiple-stage mass spectrometry (LC-ESI/HRMSn), allowing the identification of 32 compounds, never identified in A. crinitum. Metabolites belonging to the classes of organic acids, megastigmanes, phenylpropanoids, iridoids, flavonoids, coumarins, triterpenoids, and polar lipids were putatively identified; in particular, several compoundsare reported here for the first time in Ammi genus. Considering the increasing interest for the development of botanical insecticides, the acaricidal activity of A. crinitum against the two-spotted spider mite Tetranychus urticae Koch was evaluated. Although all extracts showed promising acaricidal activity, the most effective was the extract obtained from the aerial parts. The lowest LD50 and LD90 values of 2.3 and 77.3 μg‧cm−2 were estimated for this extract from aerial parts, although this LD50 was statistically identical to the LD50 of the roots extract. The extract from aerial parts not only caused the mortality of T. urticae adults, but also inhibited the fertility and fecundity of females, even when a dose of 5 μg‧cm−2 was applied. Based on our experiments, MeOH extracts from aerial parts biomass of A. crinitum can be proposed as a perspective source of active substances of potential botanical acaricides.

Monitoring detoxification enzyme levels and resistance of Tetranychus urticae against some METI-group chemicals in Türkiye cotton fields.

Acaricides used against Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) in cotton fields cause control failure over time. To determine the resistance status of T. urticae populations to tebufenpyrad and bifenazate, different populations collected from Aydın (AYD), Adana (ADA), Şanlıurfa (SAN), and Diyarbakır (DIY) provinces of Türkiye, between 2019 and 2020, were subjected to diagnostic dose bioassays. Firstly, the spider mites were eliminated with a discriminating dose. Afterwards, LC50 and LC90 of the remaining populations were determined and the ten highest resistant populations were selected. The highest phenotypic resistance to bifenazate was observed in AYD4 and DIY2 (LC50 57.14 mg L- 1 with 85.01-fold and LC50 30.15 mg L- 1with 44.86-fold, respectively), while the lowest phenotypic resistance was found in SAN6 (LC50 1.5 mg L- 1; 2.28-fold). Considering the phenotypic resistance to tebufenpyrad, the highest resistance was found in AYD4 population (LC50 96.81 mg L- 1; 12.92-fold), while the lowest - in DIY28 population (LC50 21.23 mg L- 1; 2.83-fold). In pharmacokinetic studies, the ADA16 population was compared with the sensitive German Susceptible Strain population and it was determined that carboxylesterase activity was statistically higher (1.46 ± 0.04 nmol/min/mg protein enzyme activation 2.70-fold). The highest activation of glutathione S-transferase was detected in ADA16 (1.49 ± 0.01 nmol/min/mg protein; 2.32-fold). No mutations were found in PSST (METI 1), the point mutation site for tebufenpyrad, and Cytb (METI 3), the point mutation site for bifenazate. In terms of phenotypic resistance, bifenazate was found to be moderately resistant in two populations (85.01 and 44.86-fold), while tebufenpyrad was moderately resistant in one population (12.92-fold). This study showed that both acaricides are still effective against T. urticae populations.

Enhancing retinal fundus image classification through Active Gradient Deep Convolutional Neural Network and Red Spider Optimization

Enhancing retinal fundus image classification through Active Gradient Deep Convolutional Neural Network and Red Spider Optimization

The soybean plasma membrane GmDR1 protein conferring broad-spectrum disease and pest resistance regulates several receptor kinases and NLR proteins

Overexpression of Glycine max disease resistant 1 (GmDR1) exhibits broad-spectrum resistance against Fusarium virguliforme, Heterodera glycines (soybean cyst nematode), Tetranychus urticae (Koch) (spider mites), and Aphis glycines Matsumura (soybean aphids) in soybean. To understand the mechanisms of broad-spectrum immunity mediated by GmDR1, the transcriptomes of a strong and a weak GmDR1-overexpressor following treatment with chitin, a pathogen- and pest-associated molecular pattern (PAMP) common to these organisms, were investigated. The strong and weak GmDR1-overexpressors exhibited altered expression of 6098 and 992 genes, respectively, as compared to the nontransgenic control following chitin treatment. However, only 192 chitin- and 115 buffer-responsive genes exhibited over two-fold changes in expression levels in both strong and weak GmDR1-overexpressors as compared to the control. MapMan analysis of the 192 chitin-responsive genes revealed 64 biotic stress-related genes, of which 53 were induced and 11 repressed as compared to the control. The 53 chitin-induced genes include nine genes that encode receptor kinases, 13 encode nucleotide-binding leucine-rich repeat (NLR) receptor proteins, seven encode WRKY transcription factors, four ethylene response factors, and three MYB-like transcription factors. Investigation of a subset of these genes revealed three receptor protein kinases, seven NLR proteins, and one WRKY transcription factor genes that are induced following F. virguliforme and H. glycines infection. The integral plasma membrane GmDR1 protein most likely recognizes PAMPs including chitin and activates transcription of genes encoding receptor kinases, NLR proteins and defense-related genes. GmDR1 could be a pattern recognition receptor that regulates the expression of several NLRs for expression of PAMP-triggered immunity and/or priming the effector triggered immunity.

Sucking insect’s pest management in organic rose production

Sucking insects are the most common pests and could affect a wide range of cultural and wild plants. They possess a big reproductive potential and under favourable climatic conditions can cause considerable damages on agricultural crops. Some of the sucking insects show resistance to chemical pesticides, which additionally makes their control difficult. To investigate the effect of natural pesticides on the population of some sucking insects in a two year`s field experiment was conducted in the region of the village Kliment on five years`s old organic rose plantation. The following products have been included in the investigation: Limocide® (60 g/L orange oil) NeemAzal® T/S (Nime-substance – 2.5 %) and 4 % bee glue solution. The field experiments were arranged according to the block method in four replications and plot size of 18 м2 (21 plants per variant). The population density of sucking insects varied depending on the climate conditions. The product Limocide® and the 4% bee glue solution managed to control the invasion of the two-spotted spider mite Macrosiphum rosae L. and proved their effectiveness against Thrips tabaci as well. The product that contain as azadirachtin as an active substance showed an unsatisfactory percentage of effectiveness against the target insects. The 4% bee glue solution has a great potential, and its mechanism of action needs to be further investigated. Keywords: biological control, sucking insects, roses

First Report of Tetranychus truncatus Ehara (Acari: Tetranychidae) Infesting Groundnut (Arachis hypogaea L.) in India through Morphological and Molecular Insight

Background: Red spider mite, Tetranychus truncatus Ehara (Acari: Tetranychidae) infests many agriculture and horticulture crops in India, but to date it had not been found damaging cultivated groundnut. During 2022-23, the incidence of this species was high in many groundnut growing regions of Tamil Nadu. Identification of the species is highly essential for effective management of the particular pest. Hence, the aim of this research was to identify the mite species infesting groundnut crop and describe the damage caused. Methods: Survey was carried out all over Tamil Nadu and samples of mite infested groundnut leaves were collected from field based on damage symptoms, observed and examined under Stereo zoom microscope, microslides were prepared using Hoyer’s medium and taxonomic characters were studied under phase contrast microscope. Molecular analysis was done by genomic DNA isolation, PCR amplification, sequencing and BLAST performed to check the identity with GenBank Sequences. ITS2 primer was used. Result: Red spider mite species, T. truncatus was identified first time in groundnut through both morphological characters and molecular tools. Female: Idiosomal setae longer than the interval between their longitudinal bases and gradually tapers distally. Diamond- shaped pattern of striae between e1 and f1 setal bases. Tarsus I with 4 tactile setae proximal to proximal duplex setae. Male: Aedeagus with tiny terminal knob, apparently truncate with a slight indentation on the dorsal margin.

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.

Efficacy of Biopesticides Against <i>Tetranychus Urticae</i> Koch Infesting Dodi <i>Leptadenia Reticulata</i>

A field experiment was carried out to test the efficacy of biopesticides against the red two spotted spider mite Tetranychus urticae Koch infesting dodi (Jivanti), Leptadenia reticulata (Ret.) Wight and Aruott. The findings revealed that azadirachtin 0.15 EC was found most effective incidence (3.19/ cm2 leaf) followed by neemastra (3.27 mites/ cm2 leaf), neem oil (3.34 mites/ cm2 leaf) and neem seed kernal extract (3.42 mites/ cm2 leaf). Beauveria bassiana 5% WP (5.31 mites/ cm2 leaf), ashwagandha 7.5% leaf extract (5.37 mites/ cm2 leaf) and Metarhizium anisopliae 1.15% (5.53 mites/ cm2 leaf) were moderate in their effectiveness. Maximum incidence was noticed from the leaves treated with desi cow urine (5%).

Efficacy of Some Insecticides Aganist Fruit Borer <i>Helicoverpa Armigera</i> (Hübner) and Two Spotted Spider Mite <i>Tetranychus Urticae</i> (Koch) in Tomato

Fruit borer Helicoverpa armigera (Hübner) and two spotted spider mite, Tetranychus urticae (Koch) are destructive pests exerting a high crop loss in tomato. The field experiment was carried out to evaluate the efficacy of some insecticides and acaricides against H. armigera and T. urticae at College of Agriculture, Vijayapura. The results revealed that chlorantraniliprole 18.5% SC @ 0.15 ml/ l followed by spiromesifen 22.9% SC @ 0.5 ml/ l was recorded lowest fruit borer larvae (1.25/ plant). The treatment chlorantraniliprole 18.5% SC @ 0.15 ml/ l recorded lowest fruit damage (8.91/ plant) at 15 DAS. The treatment spiromesifen 22.9% SC @ 0.5 ml/ l recorded lowest number of two spotted spider mites (2.30/ square inch of leaf area) at 15 DAS. The combination treatment of chlorantraniliprole 18.5% SC @ 0.15 ml/ l followed by spiromesifen 22.9% SC @ 0.5 ml/ l found most effective treatment to control both the above pests on tomato.

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.

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 ABA-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 2-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 Forster resonance energy transfer (FRET)-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types postmite 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.

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.

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.

Combined application of entomopathogenic fungi and predatory mites for biological control of Tetranychus urticae on chrysanthemum.

Most studies on efficacy of fungal pathogens and predatory mites against Tetranychus urticae have been done on individual species in the laboratory. We evaluated fungi and predatory mites separately and together against glasshouse populations of T. urticae on chrysanthemum plants. First, effectiveness of the fungal pathogens Beauveria bassiana (Bb88) and Metarhizium anisopliae (Ma129) was compared; then, effectiveness of the predatory mites Phytoseiulus persimilis and Neoseiulus californicus. Based on the results, N. californicus and isolate Ma129 were selected and evaluated in combination. In all experiments, treatment effects were assessed for eggs and motile stages of T. urticae. The first experiment showed no significant effect of either fungal isolate on T. urticae populations, except on plants initially infested with 20 mites, where more eggs were found in the control compared to the fungal treatments. In the second experiment, both predatory mites were equally effective at reducing T. urticae populations compared with the control, regardless of initial T. urticae population density. The last experiment demonstrated that populations of T. urticae were reduced most when M. anisopliae (Ma129) and N. californicus were applied together, compared with the control and when each natural enemy was applied separately. Metarhizium anisopliae (Ma129) and B. bassiana (Bb88) isolates did not have a significant effect on reducing T. urticae populations. Both predatory mites reduced T. urticae populations, regardless of T. urticae density. Combined application of M. anisopliae (Ma129) and N. californicus were more effective against T. urticae than the control or when each agent was applied separately. © 2024 Society of Chemical Industry.

A novel target-site mutation (H146Q) outside the ubiquinone binding site of succinate dehydrogenase confers high levels of resistance to cyflumetofen and pyflubumide in Tetranychus urticae

Mitochondrial electron transfer inhibitors at complex II (METI-II), also referred to as succinate dehydrogenase inhibitors (SDHI), represent a recently developed class of acaricides encompassing cyflumetofen, cyenopyrafen, pyflubumide and cyetpyrafen. Despite their novelty, resistance has already developed in the target pest, Tetranychus urticae. In this study a new mutation, H146Q in a highly conserved region of subunit B of complex II, was identified in a T. urticae population resistant to all METI-IIs. In contrast to previously described mutations, H146Q is located outside the ubiquinone binding site of complex II. Marker-assisted backcrossing of this mutation in a susceptible genetic background validated its association with resistance to cyflumetofen and pyflubumide, but not cyenopyrafen or cyetpyrafen. Biochemical assays and the construction of inhibition curves with isolated mitochondria corroborated this selectivity. In addition, phenotypic effects of H146Q, together with the previously described H258L, were further examined via CRISPR/Cas9 gene editing. Although both mutations were successfully introduced into a susceptible T. urticae population, the H146Q gene editing event was only recovered in individuals already harboring the I260V mutation, known to confer resistance towards cyflumetofen. The combination of H146Q + I260V conferred high resistance levels to all METI-II acaricides with LC50 values over 5000 mg a.i./L for cyflumetofen and pyflubumide. Similarly, the introduction of H258L via gene editing resulted in high resistance levels to all tested acaricides, with extreme LC50 values (>5000 mg a.i./L) for cyenopyrafen and cyetpyrafen, but lower resistance levels for pyflubumide and cyflumetofen. Together, these findings indicate that different mutations result in a different cross-resistance spectrum, probably also reflecting subtle differences in the binding mode of complex II acaricides.