RESUMEN

A newly developed pesticide, flupentiofenox, has a unique trifluoroethyl phenylsulfoxide structure, and it powerfully affects spider mites, including those with resistance to multiple commercial acaricides. To clarify the mode of action of flupentiofenox, we investigated its effect on mitochondrial energy generation. We observed that flupentiofenox decreased adenosine triphosphate (ATP) levels in two-spotted spider mites (Tetranychus urticae) at a practical dose. Flupentiofenox potently inhibited mitochondrial oxygen consumption under conditions of palmitoyl-carnitine or octanoic acid supply, but not under conditions of pyruvate supply. These results show that flupentiofenox inhibits the mitochondrial fatty acid metabolic pathway between the uptake of long-chain acylcarnitine or medium-chain fatty acid and the synthesis of acetyl-CoA by ß-oxidation, resulting in suppressed mitochondrial energy generation. Our investigations have led us to conclude that flupentiofenox is a pesticide with a novel mode of action.

Asunto(s)

RESUMEN

The diet breadth of generalist herbivores when compared to specialists tends to be associated with greater transcriptional plasticity. Here, we consider whether it may also contribute to variation in host range among two generalists with different levels of polyphagy. We examined two related polyphagous spider mites with different host ranges, Tetranychus urticae (1200 plants) and Tetranychus truncatus (90 plants). Data from multiple populations of both species domesticated on common beans and transferred to new plant hosts (cotton, cucumber, eggplant) were used to investigate transcriptional plasticity relative to population-based variation in gene expression. Compared to T. truncatus, T. urticae exhibited much higher transcriptional plasticity. Populations of this species also showed much more variable expression regulation in response to a plant host, particularly for genes related to detoxification, transport, and transcriptional factors. In response to the different plant hosts, both polyphagous species showed enriched processes of drug/xenobiotics metabolism, with T. urticae orchestrating a relatively broader array of biological pathways. Through co-expression network analysis, we identified gene modules associated with host plant response, revealing shared hub genes primarily involved in detoxification metabolism when both mites fed on the same plants. After silencing a shared hub CYP gene related to eggplant exposure, the performance of both species on the original bean host improved, but the fecundity of T. truncatus decreased when feeding on eggplant. The extensive transcriptomic variation shown by T. urticae might serve as a potential compensatory mechanism for a deficiency of hub genes in this species. This research points to nuanced differences in transcriptomic variability between generalist herbivores.

RESUMEN

Multiple cues are often used for mate choice in complex environments, potentially entailing mismatches in the information conveyed by different sources. We address the consequences of this information mismatch for receivers using the spider mite Tetranychus urticae, in which virgin females are highly valuable mates compared to mated females, given first male sperm precedence. Accordingly, males are known to prefer virgins and distinguish them using cues from the females themselves and that they leave on the substrate. Whereas cues from females are highly reliable, those left on the substrate may not reflect the real female mating status if females move and/or mate. Here, we tested the consequences of such mismatch by exposing males to mated or virgin females on patches previously impregnated with cues deposited by females of either mating status. Male mating attempts were solely affected by substrate cues while female acceptance and the number of mating events were independently affected by both cues. Copulation duration, in contrast, depended mainly on the mating status of the female, with the number of copulations and the total time spent mating being intermediate in environments with mismatched information. We also show that males incur mating costs, reflected in reduced survival in environments with virgin cues. These results suggest that substrate cues left by females are instrumental for males to find their mates. However, in environments with mismatched information, males may pay survival costs without the associated benefit of mating with virgins, or they may lose opportunities to mate with virgins by responding to substrate cues from mated females. The benefit of using multiple cues will then hinge upon the frequency of information mismatch, which itself should vary with the dynamics of populations.

RESUMEN

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.

Asunto(s)

RESUMEN

To enhance food security, food safety, and environmental health, a bio-based integrated pest management (BIPM) strategy was evaluated at two coastal locations in Lebanon as an alternative to toxic pesticide sprays in commercial high-arched plastic tunnels common in many countries. The evaluation occurred during two cucumber and pepper cropping seasons: spring and fall. At each site, two commercial tunnels were used; farmers' conventional practices were applied in one tunnel, while the BIPM approach was followed in the second tunnel. In the farmers' practices, a total of 14 sprays of insecticide/acaricide mixtures were applied during the spring growing season, and 6 sprays were applied during the fall. In the BIPM tunnels, hotspot releases of local strains of Amblyseius swirskii and Phytoseiulus persimilis were applied. By the end of the spring season, the number of whitefly nymphs (WFNs)/leaf and thrips/leaf in the pesticide treatment were 4.8 and 0.06, respectively, compared to 0.1 and 0.33, respectively, in the BIPM treatment. Similarly, at the end of the fall season, the WFNs reached 19.7/leaf in the pesticide control as compared to 1.2/leaf in the BIPM treatment, proving the efficacy of A. swirskii. Farmers using conventional acaricides during both cropping seasons failed to control Tetranychus urticae, the two-spotted spider mite (TSSM). However, hotspot releases of P. persimilis were successful in controlling TSSM. By the end of June, the number of TSSMs reached 7.8/leaf in the BIPM treatment compared to 53/leaf in the pesticide treatment. Likewise, in December, TSSM numbers reached 9/leaf in the BIPM treatment compared to 40/leaf in the pesticide treatment. Preliminary observations of pepper showed that both predatory mites (A. swirskii and P. persimilis) gave similar or better efficacy against the three pests. The two local predatory phytoseiid mites seem to be effective in controlling these three major pests and to be adapted to local environmental conditions. A rate of increase of 0.86 was observed for P. persimilis and 0.22 for A. swirskii, in June, when maximum temperatures were close to 40 °C. This also shows a compatibility between the two predators. In conclusion, our BIPM approach was efficient under a Mediterranean climate in arched plastic tunnels with relatively poor aeration.

RESUMEN

In strawberry production, western flower thrips (WFT) and two-spotted spider mites (TSSM) inflict feeding damage and reduce the yield. Biological control for these pests often includes phytoseiid predatory mites and entomopathogenic fungi. The hemipteran family Nabidae have been reported as prominent predators in open-field strawberry. Nabis americoferus Carayon is a new biocontrol agent developed in Canada. This study examined if this species was a good candidate for integration with biological control for greenhouse strawberry production. The laboratory trials showed that Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot were compatible with N. americoferus, especially when alternative food was available. In contrast, the nabid was not compatible with the Beauveria bassiana (Balsamo) GHA strain. A greenhouse cage study was conducted to determine if it was beneficial to add N. americoferus to the phytoseiid-mites-based biological control program for WFT and TSSM in greenhouse strawberry. The release of N. americoferus on a banker plant together with the placement of sachets of Neoseiulus cucumeris (Oudemans) and Neoseiulus californicus (McGregor) was beneficial, not only potentially reducing the number of sachet applications, but also providing better pest control than phytoseiid mites alone. Neither the phytoseiids nor the N. americoferus numbers were significantly affected by the presence of each other.

RESUMEN

Jasmonates are essential modulators of plant defences but the role of JA-derivatives has been scarcely studied, particularly in the plant-pest interplay. To deepen into the JA catabolism and its impact on plant responses to spider mite infestation, we selected the Arabidopsis JAO2 gene as a key element involved in the first step of the JA-catabolic route. JAO2 is responsible for the hydroxylation of JA into 12-OH-JA, contributes to attenuate JA and JA-Ile content and consequently, determines the formation of other JA-catabolites. JAO2 was up-regulated in Arabidopsis by mite infestation. Mites also induced JA-derivative accumulation in plants. In jao2 mutant lines, and in the triple mutant jaoT (jao2-1, jao3-1, jao4-2), mite feeding produced less leaf damage, minor callose deposition and lower mite fecundity rates than in Col-0 plants. The impairment of JA oxidation in jao2 lines not only diminished the 12-OH-JA levels but turned off further sulfation as shown the significant reduction of 12-HSO4-JA form. Thus, JAO2 acts as a negative modulator of defences to spider mites mediated by changes in the generation of JA catabolic molecules, and the consequent production of defensive metabolites such as glucosinolates or camalexin.

Asunto(s)

RESUMEN

Entomopathogenic fungi have been well exploited as biocontrol agents that can kill insects through direct contact. However, recent research has shown that they can also play an important role as plant endophytes, stimulating plant growth, and indirectly suppressing pest populations. In this study, we examined the indirect, plant-mediated, effects of a strain of entomopathogenic fungus, Metarhizium brunneum on plant growth and population growth of two-spotted spider mites (Tetranychus urticae) in tomato, using different inoculation methods (seed treatment, soil drenching and a combination of both). Furthermore, we investigated changes in tomato leaf metabolites (sugars and phenolics), and rhizosphere microbial communities in response to M. brunneum inoculation and spider mite feeding. A significant reduction in spider mite population growth was observed in response to M. brunneum inoculation. The reduction was strongest when the inoculum was supplied both as seed treatment and soil drench. This combination treatment also yielded the highest shoot and root biomass in both spider mite-infested and non-infested plants, while spider mite infestation increased shoot but reduced root biomass. Fungal treatments did not consistently affect leaf chlorogenic acid and rutin concentrations, but M. brunneum inoculation via a combination of seed treatment and soil drenching reinforced chlorogenic acid (CGA) induction in response to spider mites and under these conditions the strongest spider mite resistance was observed. However, it is unclear whether the M. brunneum-induced increase in CGA contributed to the observed spider mite resistance, as no general association between CGA levels and spider mite resistance was observed. Spider mite infestation resulted in up to two-fold increase in leaf sucrose concentrations and a three to five-fold increase in glucose and fructose concentrations, but these concentrations were not affected by fungal inoculation. Metarhizium, especially when applied as soil drench, impacted the fungal community composition but not the bacterial community composition which was only affected by the presence of spider mites. Our results suggest that in addition to directly killing spider mites, M. brunneum can indirectly suppress spider mite populations on tomato, although the underlying mechanism has not yet been resolved, and can also affect the composition of the soil microbial community.

RESUMEN

Spider mites (Acari: Tetranychidae) are dangerous pests of agricultural and ornamental crops, the most economically significant of them belonging to the genera Tetranychus, Eutetranychus, Oligonychus and Panonychus. The expansion of the distribution areas, the increased harmfulness and dangerous status of certain species in the family Tetranychidae and their invasion of new regions pose a serious threat to the phytosanitary status of agro- and biocenoses. Various approaches to acarofauna species diagnosis determine a rather diverse range of currently existing methods generally described in this review. Identification of spider mites by morphological traits, which is currently considered the main method, is complicated due to the complexity of preparing biomaterials for diagnosis and a limited number of diagnostic signs. In this regard, biochemical and molecular genetic methods such as allozyme analysis, DNA barcoding, restriction fragment length polymorphism (PCR-RFLP), selection of species-specific primers and real-time PCR are becoming important. In the review, close attention is paid to the successful use of these methods for species discrimination in the mites of the subfamily Tetranychinae. For some species, e. g., the two-spotted spider mite (Tetranychus urticae), a range of identification methods has been developed - from allozyme analysis to loop isothermal amplification (LAMP), while for many other species a much smaller variety of approaches is available. The greatest accuracy in the identification of spider mites can be achieved using a combination of several methods, e. g., examination of morphological features and one of the molecular approaches (DNA barcoding, PCR-RFLP, etc.). This review may be useful to specialists who are in search of an effective system for spider mite species identification as well as when developing new test systems relevant to specific plant crops or a specific region.

RESUMEN

The phytophagous mite Tetranychus truncatus is a serious pest in East Asia but has a relatively narrower host range than the pest mite Tetranychus urticae, which can feed on over 1200 plant species. Here, we generated a high-quality chromosomal level genome of T. truncatus and compared it with that of T. urticae, with an emphasis on the genes related to detoxification and chemoreception, to explore the genomic basis underlying the evolution of host range. We also conducted population genetics analyses (in 86 females from 10 populations) and host transfer experiments (in 4 populations) to investigate transcription changes following transfer to a low-quality host (Solanum melongena, eggplant), and we established possible connections between fitness on eggplant and genes related to detoxification and chemoreception. We found that T. truncatus has fewer genes related to detoxification, transport, and chemoreception than T. urticae, with a particularly strong reduction in gustatory receptor (GR) genes. We also found widespread transcriptional variation among T. truncatus populations, which varied in fitness on eggplant. We characterized selection on detoxification-related genes through ω values and found a negative correlation between expression levels and ω values. Based on the transcription results, as well as the fitness and genetic differences among populations, we identified genes potentially involved in adaptation to eggplant in T. truncatus. Our work provides a genomic resource for this pest mite and new insights into mechanisms underlying the adaptation of herbivorous mites to host plants.

RESUMEN

BACKGROUND: Historically, integrated mite management in Washington apple orchards has focused on conservation of the predatory mite Galendromus occidentalis (Nesbitt) to reduce secondary pest mite pressure. However, pesticide use has changed to include more selective products, coinciding with a shift in the predatory mite community composition to include a new major predator, Amblydromella caudiglans (Schuster). There is evidence that A. caudiglans is more pesticide sensitive than G. occidentalis. Therefore, updates to pesticide selectivity recommendations are needed to conserve this 'new' key predator. Using bioassays, we examined the lethal (female mortality) and sublethal effects (fecundity, egg hatch, larval survival) of 4 fungicides and 11 insecticides on A. caudiglans, to determine whether existing conservation recommendations can be applied to this predatory mite. Susceptibility was compared with prior research on G. occidentalis. RESULTS: Mancozeb was the least selective fungicide tested on A. caudiglans; it caused high acute toxicity and sublethal effects. Carbaryl was the least selective insecticide and caused 100% mortality. Captan was the most selective fungicide. Chlorantraniliprole and cyantraniliprole were the most selective insecticides and therefore least likely to disrupt biological control by A. caudiglans. Non-target effects on A. caudiglans and G. occidentalis were similar, but A. caudiglans experienced higher mortality to some broad-spectrum insecticides. CONCLUSIONS: All the products tested had some non-target effects on A. caudiglans. However, A. caudiglans sensitivity to most tested pesticides was similar to that of G. occidentalis. In general, existing spray recommendations for conserving G. occidentalis can be adjusted slightly and applied to A. caudiglans conservation. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Asunto(s)

RESUMEN

DNA barcoding technology using short DNA sequences has emerged as an efficient and reliable tool for identifying, confirming, and resolving closely related taxa. This study used ITS2-rDNA and mtCOI DNA sequences to confirm the identity of eight Oligonychus species, representing 68 spider mite samples, collected mainly from Saudi Arabia (SA) and some from Mexico, Pakistan, USA, and Yemen. The intraspecific nucleotide divergences of the studied Oligonychus species ranged from 0% to 1.2% for ITS2 and 0% to 2.9% for COI. However, the interspecific nucleotide divergences were distinctly higher than the intraspecific ones and ranged from 3.7% to 51.1% for ITS2 and 3.2% to 18.1% for COI. Furthermore, molecular data correctly confirmed the species identity of 42 Oligonychus samples lacking males, including a previously claimed sample of O. pratensis from SA. High genetic variations were detected in two Oligonychus species: O. afrasiaticus (McGregor) (nine ITS2 and three COI haplotypes) and O. tylus Baker and Pritchard (four ITS2 and two COI haplotypes). In addition, ITS2- and COI-based phylogenetic trees confirmed the subdivision of the genus Oligonychus. In conclusion, integrative taxonomic approaches are vital to resolve the closely related Oligonychus species, identify the samples lacking male specimens, and assess phylogenetic relationships within and among species.

RESUMEN

The two-spotted spider mite Tetranychus urticae is a polyphagous herbivore with a worldwide distribution, and is a serious pest in tomato and other crops. As an alternative to chemical pesticides, biological control with the release of natural enemies such as predatory mites represent an efficient method to control T. urticae in many crops, but not in tomato. Other biological control agents, such as beneficial microbes, as well as chemical compounds, which can act as plant defense elicitors that confer plant resistance against pests and pathogens, may prove promising biological solutions for the suppression of spider mite populations in tomato. Here, we assessed this hypothesis by recording the effects of a series of fungal and bacterial strains and the plant strengthener acibenzolar-s-methyl for their plant-mediated effects on T. urticae performance in two tomato cultivars. We found significant negative effects on the survival, egg production and spider mite feeding damage on plants inoculated with microbes or treated with the plant strengthener as compared to the control plants. Our results highlight the potential of beneficial microbes and plant strengtheners in spider mite suppression in addition to plant disease control.

RESUMEN

Spider mites are serious pests and have evolved significant resistance to many chemical pesticides, thus making their control challenging. Several insect pests can be combated by plastid-mediated RNA interference (PM-RNAi), but whether PM-RNAi can be utilized to control noninsect pests is unknown. Here, we show that three species of spider mites (Tetranychus evansi, Tetranychus truncatus, and Tetranychus cinnabarinus) take up plastid RNA upon feeding. We generated transplastomic tomato plants expressing double-stranded RNA (dsRNA) targeted against a conserved region of the spider mite ß-Actin mRNA. Transplastomic plants exhibited high levels of resistance to all three spider mite species, as evidenced by increased mortality and suppression of target gene expression. Notably, transplastomic plants induced a more robust RNAi response, caused higher mortality, and were overall better protected from spider mites than dsRNA-expressing nuclear transgenic plants. Our data demonstrate the potential of PM-RNAi as an efficient pest control measure for spider mites and extend the application range of the technology to noninsect pests.

Asunto(s)

RESUMEN

Ras opposite (Rop) is known to play an essential role in regulating vesicle trafficking, including synaptic transmission and general secretion. The fundamental roles of Rop have been confirmed by the observation that null mutations in many organisms generate lethal phenotypes during embryogenesis. However, the effects of Rop during the postembryonic stages, especially in non-model organisms, remain largely unknown. Here, we provide new data that enhance our understanding of Rop's roles in the adults of multiple species of Tetranychus spider mites (Acari: Tetranychidae), a class of notorious agricultural pests. Our in silico and experimental evidence demonstrated that Rop is under purifying selection and is highly conserved in Tetranychus spp. RNA interference experiments showed that Rop is required for maintaining normal fecundity but has no significant effect on survival. We further demonstrate that knockdown of Rop darkens the body color of spider mites and blocks the excretion of fecal pellets, which is likely to be related to an abnormality in the excretion of food waste in the digestive system. Overall, our findings clarify novel functions of a vesicle trafficking-related gene in the adult stage of multiple Tetranychus species and highlight the need to evaluate the roles of essential genes in various organisms.

Asunto(s)

RESUMEN

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is the most economically important mite pest in agricultural areas and chemical acaricides are widely used to control T. urticae populations. Cyflumetofen is a recently introduced acaricide that inhibits the mitochondrial electron transport chain at complex II (succinate dehydrogenase, SDH), which represents the most recently developed mode of action for mite control worldwide. In the present study, started upon the launch of cyflumetofen in Turkey, a five-year survey was performed to monitor cyflumetofen susceptibility in 28 T. urticae populations collected from agricultural fields across the country. The first resistance case that might cause control failure in practical field conditions was uncovered in 2019, three years after the registration of cyflumetofen. In addition, an extremely resistant population (1722-fold resistance) was also detected towards the end of 2019. Cyflumetofen resistance did not decrease in the laboratory after relaxation of selection pressure for over one year in field-collected populations, suggesting the absence of a fitness cost associated with resistance in these populations. Next to phenotypic resistance, metabolic and physiological mechanisms underlying the decreased susceptibility were also investigated. Synergism assays showed the involvement of P450 monooxygenases in cyflumetofen resistance. Downregulation of carboxylesterases as resistance mechanism, is underpinned by the fact that pre-treatment with esterase inhibitor DEF decreased cyflumetofen toxicity in field-collected strains. Furthermore, a novel H258L substitution in the subunit B of complex II was uncovered in a field population. In silico modeling of the new mutation suggested that the mutation might indeed influence toxicity to complex II inhibitors cyenopyrafen and pyflubumide, but most likely not cyflumetofen. However, further studies are needed to uncover the exact role of this mutation in resistance to this new class of complex II inhibitors.

Asunto(s)

RESUMEN

Only two species of the genus Stylophoronychus, S. baghensis (Prasad, 1975) and S. guangzhouensis (Ma and Yuan, 1980), have been recorded in China. Herein we describe a new species Stylophoronychus wangaePan, Jin & Yi sp. nov. based on characteristics of the deutonymphs and adults. The synonym of S. guangzhouensis (Ma and Yuan, 1980) and S. lalli (Prasad, 1975) with S. vannus (Rimando, 1968) is proposed. A redescription of S. vannus (Rimando, 1968) based on the adults of both sexes, deutonymphs and a protonymph is given. The ontogenetic changes of leg chaetotaxy in two species are given and discussed. The updated key to the species of Stylophoronychus of the world is provided.

RESUMEN

The almond crop in Spain has increased in importance in recent years and consequently there is a need to improve knowledge about pests, diseases, and weeds. The present study was conducted from 2017 to 2020, with the objective of determining the fauna of spider mites and their natural enemies, with a special emphasis on phytoseiids. The main spider mite species was Tetranychus urticae Koch, and secondary species were Bryobia rubrioculus (Scheuten) and Eutetranychus banksii (McGregor). Phytoseiidae were the most abundant group of natural enemies, with 59% of the individuals observed; Euseius stipulatus (Athias-Henriot) was the predominant species, accounting for 96% of adult females identified, Typhlodromus (Anthoseius) athenas Swirski & Ragusa accounted for the remaining 4%. Other (potential) natural enemies were Chrysopidae, Scolothrips longicornis Priesner, and Stethorus sp. with 36, 2, and 3%, respectively, of the natural enemy individuals. The seasonal pattern of T. urticae indicated population peaks from July to September, and its control was based on miticides in most seasons. Euseius stipulatus and T. athenas appeared mainly in May-June and did not show interaction with the spider mite population. Chrysopidae were present throughout the season, from May to October in the 4 years, but no direct relationship with the spider mite population was observed. In contrast, the seasonal pattern of both S. longicornis and Stethorus sp. coincided with the most important peaks of spider mites and these predators were seen in the spider mite colonies, although in very low numbers. The importance of these latter specialized spider mite predators and ways to strengthen them are discussed.

Asunto(s)

RESUMEN

Spider mites become easy prey for ants when they leave their protective webs; therefore, the ability to avoid traces of ongoing ant activity should confer a selective advantage to mites. We examined avoidance of ant traces by the spider mites Tetranychus kanzawai and Tetranychus urticae. Both mite species avoided host plant leaves with active traces of Pristomyrmex punctatus or Formica japonica ants. Pristomyrmex punctatus trace avoidance by T. kanzawai lasted for more than 1 h, but not more than 3 h. Tetranychus kanzawai also avoided P. punctatus traces on plant stems, along which the mites access leaves. Moreover, T. kanzawai avoided hexane extracts of P. punctatus or F. japonica applied to a filter paper pathway. This study represents the first demonstration of a repellent effect of ant chemical traces on spider mites. Considering the substantial abundance and global distribution of ants in nature, such repellent effects may help to answer the long-standing question of why only a small fraction of available plant resources is used by herbivores. Although spider mites have developed resistance against many synthetic pesticides, natural compounds that simulate ant chemical traces may repel spider mites from agricultural crops.

Asunto(s)

RESUMEN

In recent years, spider mites have caused considerable economic losses to global agriculture. However, currently available management strategies are limited because of the rapid development of resistance. In this study, Bacillus vallismortis NBIF-001 was isolated and evaluated for its acaricidal activity. NBIF-001 exhibited a significant lethal effect on spider mites within 48 h. The median lethal concentration (LC50) of the culture powders (3.2 × 1010 CFU/g) was 50.2 µg/mL for Tetranychus urticae (red form), 18.0 µg/mL for T. urticae (green form), and 15.7 µg/mL for Panonychus citri (McGregor). Cultivation optimisation experiments showed that when the number of spores increased, fermentation toxicity also increased. Moreover, field experiments demonstrated that NBIF-001 performed well in the biocontrol of P. citri, which showed a similar corrected field efficacy with the chemical control (67.1 ± 7.9% and 71.1 ± 6.4% after 14 days). Genomics analysis showed that NBIF-001 contains 231 factors and seven gene clusters of metabolites that may be involved in its acaricidal activity. Further bioassays of the fermentation supernatants showed that 50× dilution treatments killed 72.5 ± 5.4% of the mites in 48 h, which was similar with those of the broth. Bioassays of the supernatant proteins confirmed that various proteins exhibited acaricidal activity. Five candidate proteins were expressed and purified successfully. The bioassays showed that the small protein BVP8 exhibited significant acaricidal activity with an LC50 of 12.4 µg/mL (T. urticae). Overall, these findings suggest that B. vallismortis NBIF-001 is a potential biocontrol agent for spider mite management.