Insecticidal efficacy and mechanism of nanoparticles synthesized from chitosan and carboxymethyl chitosan against Solenopsis invicta (Hymenoptera: Formicidae)

Inhibition mechanism of Rhizoctonia solani by pectin-coated iron metal-organic framework nanoparticles and evidence of an induced defense response in rice

Nanocrop protectants have attracted much attention as sustainable platforms for controlling pests and diseases and improving crop nutrition. Here, we reported the fungicidal activity and disease inhibition potential of pectin-coated metal-iron organic framework nanoparticles (Fe-MOF-PT NPs) against rice stripe blight (RSB). An in vitro bacterial inhibition assay showed that Fe-MOF-PT NPs (80 mg/L) significantly inhibited mycelial growth and nucleus formation. The Fe-MOF-PT NPs adsorbed to the surface of mycelia and induced toxicity by disrupting cell membranes, mitochondria, and DNA. The results of a nontargeted metabolomics analysis showed that the metabolites of amino acids and their metabolites, heterocyclic compounds, fatty acids, and nucleotides and their metabolites were significantly downregulated after treatment with 80 mg/L NPs. The difference in metabolite abundance between the CK and Fe-MOF-PT NPs (80 mg/L) treatment groups was mainly related to nucleotide metabolism, pyrimidine metabolism, purine metabolism, fatty acid metabolism, and amino acid metabolism. The results of the greenhouse experiment showed that Fe-MOF-PT NPs improved rice resistance to R. solani by inhibiting mycelial invasion, enhancing antioxidant enzyme activities, activating the jasmonic acid signaling pathway, and enhancing photosynthesis. These findings indicate the great potential of Fe-MOF-PT NPs as a new RSB disease management strategy and provide new insights into plant fungal disease management.

Green synthesized lignin nanoparticles for the sustainable delivery of pyraclostrobin to control strawberry diseases caused by Botrytis cinerea

Lignin, renowned for its renewable, biocompatible, and environmentally benign characteristics, holds immense potential as a sustainable feedstock for agrochemical formulations. In this study, raw dealkaline lignin (DAL) underwent a purification process involving two sequential solvent extractions. Subsequently, an enzyme-responsive nanodelivery system (Pyr@DAL-NPs), was fabricated through the solvent self-assembly method, with pyraclostrobin (Pyr) loaded into lignin nanoparticles. The Pyr@DAL-NPs shown an average particle size of 250.4 nm, demonstrating a remarkable loading capacity of up to 54.70 % and an encapsulation efficiency of 86.15 %. Notably, in the presence of cellulase and pectinase at a concentration of 2 mg/mL, the release of Pyr from the Pyr@DAL-NPs reached 92.66 % within 120 h. Furthermore, the photostability of Pyr@DAL-NPs was significantly improved, revealing a 2.92-fold enhancement compared to the commercially available fungicide suspension (Pyr SC). Bioassay results exhibited that the Pyr@DAL-NPs revealed superior fungicidal activity against Botrytis cinerea over Pyr SC, with an EC50 value of 0.951 mg/L. Additionally, biosafety assessments indicated that the Pyr@DAL-NPs effectively declined the acute toxicity of Pyr towards zebrafish and posed no negative effects on the healthy growth of strawberry plants. In conclusion, this study presents a viable and promising strategy for developing environmentally friendly controlled-release systems for pesticides, offering the unique properties of lignin.

The evaluation of mixed-layer emulsions stabilized by myofibrillar protein-chitosan complex for delivering astaxanthin: Fabrication, characterization, stability and in vitro digestibility

Muscle protein based functional foods have been attracted great interests in novel food designing. Herein, myofibrillar protein (MP)-chitosan (CH) electrostatic complexes were employed to fabricate mixed-layer emulsions to protect and deliver astaxanthin. The MP/CH complex fabricated mixed-layer emulsions displayed higher stability against pH and temperature changes, exhibiting smaller droplet and homogenous distributions. After UV-light irradiation for 8 h, the mixed-layer emulsions had higher astaxanthin retention (69.11 %, 1:1 group). During storage, a lower degree of lipid oxidation, protein oxidation and higher astaxanthin retention were obtained, indicating desirable protections of mixed-layer emulsions. The vitro digestion reveled the mixed-layer emulsions could decrease the release of free fatty acids. Meanwhile, the bioaccessibility of astaxanthin was higher (30.43 %, 2:1 group) than monolayer emulsion. In all, the MP/CH prepared mixed-layer emulsions could protect and deliver fat-soluble bioactive compounds, and contributed to develop muscle protein based functional foods to meet the needs of slow and controlled release.

Pectin-Coated Iron-Based Metal-Organic Framework Nanoparticles for Enhanced Foliar Adhesion and Targeted Delivery of Fungicides

Conventional agrochemicals are underutilized due to their large particle sizes, poor foliar retention rates, and difficult translocation in plants, and the development of functional nanodelivery carriers with high adhesion to the plant body surface and efficient uptake and translocation in plants remains challenging. In this study, a nanodelivery system based on a pectin-encapsulated iron-based MOF (TF@Fe-MOF-PT NPs) was constructed to enhance the utilization of thifluzamide (TF) in rice plants by taking advantage of the pectin affinity for plant cell walls. The prepared TF@Fe-MOF-PT NPs exhibited an average particle size of 126.55 nm, a loading capacity of 27.41%, and excellent dual-stimulus responses to reactive oxygen species and pectinase. Foliar washing experiments showed that the TF@Fe-MOF-PT NPs were efficiently adhered to the surfaces of rice leaves and stems. Confocal laser scanning microscopy showed that fluorescently labeled TF@Fe-MOF-PT NPs were bidirectionally delivered through vascular bundles in rice plants. The in vitro bactericidal activity of the TF@Fe-MOF-PT NPs showed better inhibitory activity than that of a TF suspension (TF SC), with an EC50 of 0.021 mg/L. A greenhouse test showed that the TF@Fe-MOF-PT NPs were more effective than TF SC at 7 and 14 d, with control effects of 85.88 and 78.59%, respectively. It also reduced the inhibition of seed stem length and root length by TF SC and promoted seedling growth. These results demonstrated that TF@Fe-MOF-PT NPs can be used as a pesticide nanodelivery system for efficient delivery and intelligent release in plants and applied for sustainable control of pests and diseases.

A Pyr-loaded polymer microparticle for effectively controlling Solenopsis invicta (Hymenoptera: Formicidae) in the nest

Human interference and incorrect use of pesticides are easy to induce red imported fire ant (RIFA) escape and migrate from a nest, resulting in ineffective control of RIFA. In order to avoid RIFA alert, we designed an amphiphilic PSI-mPEG-Boc-DAH loaded Pyr to make the microparticles with effective controlled release. The investigation showed that the quantity of Pyr released by Pyr@PSI-mPEG-Boc-DAH under acidic environment was only 36.40 ± 1.90% at 48 h, whereas the release rate of original Pyr was 75.23 ± 5.71%. And the RIFA mortality rate of 1 ppm Pyr in Pyr@PSI-mPEG-Boc-DAH microparticles at 48 h was only 7.78%, which was significantly lower than that of the Pyr (47.78%). Futhermore, the death rate increased sharply after 48 h, and reached 95.84% within a week after using Pyr@PSI-mPEG-Boc-DAH microparticles. Moreover, PSI-mPEG-Boc-DAH carriers could be absorbed and even transported to crop of the RIFA for subsequent trophallaxis by using fluorescence tracking. In the field experiment, the reduction rate of Pyr@PSI-mPEG-Boc-DAH treatment was achieved 99.89% after 7 d. Pyr@PSI-mPEG-Boc-DAH didn't cause RIFA to be alarmed within 48 h and could kill nearly all of ants in the nest after 7 d, which showed a very good control effect in the field experiment. This work provided a new idea and guidance for the effective control RIFA and the development of sustainable agriculture.

Survival, growth and digestive functions after exposure to nanodiamonds - Transgenerational effects beyond contact time in house cricket strains

The long-term exposure effects of nanodiamonds (NDs), spanning an organism's entire lifespan and continuing for subsequent generation, remain understudied. Most research has focused on evaluating their biological impacts on cell lines and selected organisms, typically over short exposure durations lasting hours or days. The study aimed to assess growth, mortality, and digestive functions in wild (H) and long-lived (D) strains of Acheta domesticus (Insecta: Orthoptera) after two-generational exposure to NDs in concentrations of 0.2 or 2 mg kg-1 of food, followed by their elimination in the third generation. NDs induced subtle stimulating effect that depended on the strain and generation. In the first generation, more such responses occurred in the H than in the D strain. In the first generation of H strain insects, contact with NDs increased survival, stimulated the growth of young larvae, and the activity of most digestive enzymes in mature adults. The same doses and exposure time did not cause similar effects in the D strain. In the first generation of D strain insects, survival and growth were unaffected by NDs, whereas, in the second generation, significant stimulation of those parameters was visible. Selection towards longevity appears to support higher resistance of the insects to exposure to additional stressor, at least in the first generation. The cessation of ND exposure in the third generation caused potentially harmful changes, which included, e.g., decreased survival probability in H strain insects, slowed growth of both strains, as well as changes in heterochromatin density and distribution in nuclei of the gut cells in both strains. Such a reaction may suggest the involvement of epigenetic inheritance mechanisms, which may become inadequate after the stress factor is removed.

Concentration- and Time-Dependent Dietary Exposure to Graphene Oxide and Silver Nanoparticles: Effects on Food Consumption and Assimilation, Digestive Enzyme Activities, and Body Mass in Acheta domesticus

The advancement of nanotechnology poses a real risk of insect exposure to nanoparticles (NPs) that can enter the digestive system through contaminated food or nanopesticides. This study examines whether the exposure of model insect species-Acheta domesticus-to increasing graphene oxide (GO) and silver nanoparticle (AgNP) concentrations (2, 20, and 200 ppm and 4, 40, and 400 ppm, respectively) could change its digestive functions: enzymes' activities, food consumption, and assimilation. We noticed more pronounced alterations following exposure to AgNPs than to GO. They included increased activity of α-amylase, α-glucosidase, and lipase but inhibited protease activity. Prolonged exposure to higher concentrations of AgNPs resulted in a significantly decreased food consumption and changed assimilation compared with the control in adult crickets. A increase in body weight was observed in the insects from the Ag4 group and a decrease in body weight or no effects were observed in crickets from the Ag40 and Ag400 groups (i.e., 4, 40, or 400 ppm of AgNPs, respectively), suggesting that even a moderate disturbance in nutrient and energy availability may affect the body weight of an organism and its overall condition. This study underscores the intricate interplay between NPs and digestive enzymes, emphasizing the need for further investigation to comprehend the underlying mechanisms and consequences of these interactions.

Green synthesis of a chlorfenapyr chitosan nanopesticide for maize root application: Reducing environmental pollution and risks to nontarget organisms

Chlorfenapyr (CHL) is a pyrrole insecticide with a novel structure that is used to control resistant pests. However, its weak systemic activity limits its application to crop roots. Herein, a novel CHL formulation with improved effective utilization rates and suitability for root application is developed to avoid or reduce contamination caused by pesticide spraying. Accordingly, we prepared CHL@CS/CMCS nanoparticle (NP) suspensions with a particle size of approximately 100 nm using chitosan (CS) and carboxymethyl chitosan (CMCS). These suspensions exhibited better thermal stability, adhesion, permeability and systemic activity than a CHL suspension concentrate (CHL-SC). The nanoformulation deposition rate on maize leaves after spraying was 12.28 mg/kg, significantly higher than that of CHL-SC. The nanosuspension was effectively absorbed and transported by roots after irrigation and was suitable for root application. The efficacy was 89.46-92.36 % against Spodoptera frugiperda at 7 d, 7.5-17.5 times higher than that of CHL-SC. Furthermore, the CHL@CS/CMCS nanosuspension was safer for earthworms. These results suggest that chitosan-based nanoformulations improve the efficacy, utilization efficiency and active period of CHL control, providing a new approach for CHL application, reducing pollutant dispersal and the environmental impacts of pesticide application and facilitating sustainable agricultural production.

Chitosan-based nanopesticides enhanced anti-fungal activity against strawberry anthracnose as "sugar-coated bombs"

A chitosan-based nanoparticle was prepared using chitosan (CS) and O-carboxymethyl chitosan (O-CMCS). Our study revealed that chitosan/O-carboxymethyl chitosan/tebuconazole nanoparticles (CS/O-CMCS/TBA NPs) exhibited superior antifungal activity, foliar adhesion, and microbial target adhesion performance compared to commercial suspension concentrate (SC). The antifungal activity of CS/O-CMCS/TBA NPs against C. gloeosporioides, with a 3.13-fold increase in efficacy over TBA (SC). We also found that low concentrations of CS/O-CMCS NPs promoted the growth of C. gloeosporioides and enhanced the fungal catabolism of chitosan. Overall, the CS/O-CMCS/TBA NPs were found to possess the remarkable capability to selectively aggregate around pathogenic microorganisms and CS/O-CMCS NPs can enhance the fungal catabolism of chitosan. CS/O-CMCS/TBA NPs, as a "sugar-coated bomb", was a promising asset for effective plant disease management and pesticide utilization through the affinity of chitosan-based nanoparticles and C. gloeosporioides, enabling targeted delivery and targeted release of their encapsulated active ingredient, which was important for the development and application of biocompatible chitosan-based nanopesticides.

Chitosan-induced biotic stress tolerance and crosstalk with phytohormones, antioxidants, and other signalling molecules

Several polysaccharides augment plant growth and productivity and galvanise defence against pathogens. Such elicitors have ecological superiority over traditional growth regulators, considering their amplified biocompatibility, biodegradability, bioactivity, non-toxicity, ubiquity, and inexpensiveness. Chitosan is a chitin-derived polysaccharide that has recently been spotlighted among plant scientists. Chitosan supports plant growth and development and protects against microbial entities such as fungi, bacteria, viruses, nematodes, and insects. In this review, we discuss the current knowledge of chitosan's antimicrobial and insecticidal potential with recent updates. These effects are further explored with the possibilities of chitosan's active correspondence with phytohormones such as jasmonic acid (JA), salicylic acid (SA), indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA). The stress-induced redox shift in cellular organelles could be substantiated by the intricate participation of chitosan with reactive oxygen species (ROS) and antioxidant metabolism, including hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, we propose how chitosan could be intertwined with cellular signalling through Ca2+, ROS, nitric oxide (NO), transcription factors (TFs), and defensive gene activation.

Eco-friendly deacetylated chitosan base siRNA biological-nanopesticide loading cyromazine for efficiently controlling Spodoptera frugiperda

Spodoptera frugiperda is a serious threat to various crops, such as corn and rice, and results in severe economic losses. Herein, a chitin synthase sfCHS highly expressed in the epidermis of S. frugiperda was screened, and when interfered by an sfCHS-siRNA nanocomplex, most individuals could not ecdysis (mortality rate 53.3 %) or pupate (abnormal pupation 80.6 %). Based on the results of structure-based virtual screening, cyromazine (CYR, binding free energy -57.285 kcal/mol) could inhibit ecdysis (LC₅₀, 19.599 μg/g). CYR-CS/siRNA nanoparticles encapsulating CYR and SfCHS-siRNA with chitosan (CS) were successfully prepared, as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and 74.9 mg/g CYR was characterized in the core of CYR-CS/siRNA by high-performance liquid chromatography and Fourier transform infrared spectroscopy. Small amounts of prepared CYR-CS/siRNA containing only 1.5 μg/g CYR could better inhibit chitin synthesis in the cuticle and peritrophic membrane (mortality rate 84.4 %). Therefore, chitosan/siRNA nanoparticle-loaded pesticides were useful for pesticide reduction and comprehensive control of S. frugiperda.

Azadirachtin inhibits the development and metabolism of the silk glands of Spodoptera frugiperda and affects spinning behavior

BACKGROUND

Spodoptera frugiperda is a major agricultural pest, and the dispersal of its larvae by spinning silk is one of the causes of crop damage. At present, there are relatively few reports of pest control that affect larvae spinning silk. In this study, the effect of spinning behavior of the S. frugiperda larvae was investigated through a series of experiments.

RESULTS

The 3rd instar larvae of S. frugiperda were exposed to azadirachtin, and the pathological changes in the silk glands of S. frugiperda and the differences in their metabolites were analyzed by scanning electron microscopy, histological sectioning, transmission electron microscopy and metabolomics. The results showed that azadirachtin could affect the silk gland of S. frugiperda. After 48 h of treatment with azadirachtin, the silk gland lumen of S. frugiperda appeared vacuolated. KEGG showed that 31 different metabolites were identified, of which 12 were upregulated and 19 were downregulated. These metabolites were enriched in 15 different metabolic pathways, which indicated that the silk gland of S. frugiperda was closely related to the formation of fatty acids and energy metabolism for the silk formation process.

CONCLUSIONS

This study provides a preliminary report of the effect of azadirachtin on the spinning behavior of the S. frugiperda larvae. Metabolomic results indicated that histidine, glycine and leucine, which are related to serine protein synthesis, were down-regulated. Azadirachtin can damage the silk glands of S. frugiperda and thus affect spinning behavior. This provides the basis for the control of S. frugiperda by spinning silk. © 2022 Society of Chemical Industry.

pH-responsive release and washout resistance of chitosan-based nano-pesticides for sustainable control of plumeria rust

Controlled pesticide release in response to environmental stimuli by encapsulating pesticides in a carrier is a feasible approach to improve the effective utilization rate. In this study, pH-responsive release nanoparticles loaded with penconazole (PE) were prepared by ionic cross-linking of chitosan and carboxymethyl chitosan (PE@CS/CMCS-NPs). PE@CS/CMCS-NPs exhibited good washout resistance and wettability properties, increasing the washing resistance of the pesticide by approximately 20 times under continuous washing. The results of the release experiments showed that nanoparticles had adjustable controlled-release characteristics with the change in pH based on the swelling of nanoparticles. The results of spore germination experiments showed that PE@CS/CMCS-NPs enhanced the inhibitory effect under acidic conditions. The field experiment results showed that PE@CS/CMCS-NPs had a better control effect than PE-aqueous solution, extended the duration and slowed down the dissipation of PE. These results indicated that the CS/CMCS-NPs pH-responsive release system has great potential in the development of an effective pesticide formulation.

Novel application of biodegradable chitosan in agriculture: Using green nanopesticides to control Solenopsis invicta

Botanical pesticides are biological pesticides that are environment friendly. However, their instability and short persistence limit their application. In this study, pH sensitive chitosan based rotenone (Rot) nanoparticles (CS/CMCS/Rot-NPs) were prepared using chitosan and carboxymethyl chitosan to take advantage of the acidic nature of the red fire ant midgut. Chitosan based nanoparticles showed photoprotective and slow sustained release effects on Rot and significantly increased the insecticidal activity of Rot against red fire ants. The 24-96hLC₅₀ of CS/CMCS/Rot-NPs against red fire ants was 3.28-6.84 fold that of Rot. The CS/CMCS/Rot-NPs significantly reduced the venom alkaloid content of red fire ants and their living environment and weakened their survival by increasing their survival cost in the ecological environment. Nanotechnology combined with botanical pesticides can be used as a novel, safe, effective, and ecofriendly method to control red fire ants.

Nanotechnology-Based Bioactive Antifeedant for Plant Protection

The productivity of vegetable crops is constrained by insect pests. The search for alternative insect pest control is becoming increasingly important and is including the use of plant-derived pesticides. Plant-derived pesticides are reported as effective in controlling various insect pests through natural mechanisms, with biodegradable organic materials, diverse bioactivity, and low toxicity to non-target organisms. An antifeedant approach for insect control in crop management has been comprehensively studied by many researchers, though it has only been restricted to plant-based compounds and to the laboratory level at least. Nano-delivery formulations of biopesticides offer a wide variety of benefits, including increased effectiveness and efficiency (well-dispersion, wettability, and target delivery) with the improved properties of the antifeedant. This review paper evaluates the role of the nano-delivery system in antifeedant obtained from various plant extracts. The evaluation includes the research progress of antifeedant-based nano-delivery systems and the bioactivity performances of different types of nano-carrier formulations against various insect pests. An antifeedant nano-delivery system can increase their bioactivities, such as increasing sublethal bioactivity or reducing toxicity levels in both crude extracts/essential oils (EOs) and pure compounds. However, the plant-based antifeedant requires nanotechnological development to improve the nano-delivery systems regarding properties related to the bioactive functionality and the target site of insect pests. It is highlighted that the formulation of plant extracts creates a forthcoming insight for a field-scale application of this nano-delivery antifeedant due to the possible economic production process.