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.

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.

The synergistic effects of rosehip oil and matrine against Icerya aegyptiaca (Douglas) (Hemiptera: Coccoidea) and the underlying mechanisms.

BACKGROUND: Icerya aegyptiaca (Douglas) is an important agricultural pest that has a protective wax shell. Insecticides generally fail to achieve the desired control of I. aegyptiaca because of difficulties penetrating this wax shell. Plant essential oils are rich in terpenoids and have strong penetrability and expansibility, which can enable the rapid penetration and absorption of insecticides, thereby improving the control effect. Matrine is a botanical insecticide with contact and stomach toxicity, low toxicity toward non-target organisms and is environmentally friendly. In this study, we tested the insecticidal activity of rosehip oil (Ro)/matrine combinations and revealed the synergistic mechanism of Ro and its components with matrine in terms of physiology and biochemistry. RESULTS: Ro/matrine combinations have strong penetrating power, enabling matrine to quickly penetrate the wax shell of I. aegyptiaca and enter the insect body. This improves the insecticidal activity and enhances inhibition of acetylcholinesterase activity. Ro and its main chemical constituents, cineole and (+)-camphor, showed synergistic effects on matrine with synergic ratios of 4.79, 3.49 and 4.21, respectively. CONCLUSION: Combinations of Ro, cineole and (+)-camphor with matrine have good insecticidal effects on I. aegyptiaca while remaining safe to the environment. These combinations of biological insecticides have excellent development prospects and provide a new reference for the pest management of scale insects. © 2022 Society of Chemical Industry.

Dissipation and residue of fosthiazate in tomato and cherry tomato and a risk assessment of dietary intake.

In this study, the safety and risk of fosthiazate as a nematicide against root-knot nematode in tomato and cherry tomato were evaluated. The dissipation and residue of fosthiazate for 28 days in tomatoes and cherry tomatoes were determined and studied by HPLC after simple, rapid pre-treatment. The mean recovery was 83.79~94.18%, and the relative standard deviations were 3.97~7.40%. Results showed that the half-lives of fosthiazate in tomatoes (4.81~5.37 days) were significantly lower than that in cherry tomatoes (5.25~5.73 days). At the pre-harvest interval (PHI) of 21 days, the residues of tomatoes and cherry tomatoes were 0.032~0.046 mg/kg, which were lower than the maximum residue level (MRL) established in China. The potential risks of fosthiazate exposure through the dietary intake of tomatoes and cherry tomatoes to different populations were also studied. According to the results of dietary risk assessment, the residual levels of fosthiazate were within the acceptable range of long-term dietary risk in different populations in China within the sampling interval of 21 days after the application of fosthiazate. Our results show that fosthiazate at 2250 g.a.i./ha in the field control of root-knot nematode has high safety and low risk, and can provide a reference for the safe and reasonable use of fosthiazate as a nematicide in the field.

Effects of sublethal azadirachtin on the immune response and midgut microbiome of Apis cerana cerana (Hymenoptera: Apidae).

As a wildly used plant-derived insecticide, azadirachtin (AZA) is commonly reported as harmless to a range of beneficial insects. However, with the research on the effect of AZA against pollinators in recent years, various negative physiological effects on other Apidae species have been demonstrated. Thus to explore the safety of azadirachtin to Apis cerana cerana, the different physiological effects of sublethal concentration of azadirachtin on worker bees A.c.cerana has been studied. With the exposure of 5 mg·L-1 and 10 mg·L-1 azadirachtin for 5 d, the relative expression of Apidaecin, Abaecin and Lysosome genes in workers has decreased significantly at 1, 2,3 and 5 d, and the mRNA levels of Defensin 2 and Hymenoptaecin were also significantly inhibited by 10 mg·L-1 azadirachtin at each check point. Besides, the activity of midgut antioxidant enzymes Superoxide Dismutase (SOD) and Catalase (CAT) which are the first line of defence in antioxidant systems was not affected by AZA, the activity of Peroxidase (POD) showed a fluctuating pattern at 24 h and 48 h, while the activity of polyphenol oxidase (PPO) has significantly inhibited by AZA. However, through 16sRNA analysis it was observed that 5 mg·L-1 AZA did not affect the midgut microbiome colony composition and relative abundance, as well as its main function. Therefore, to a certain extent, azadirachtin is safe for workers, but we should pay more attention to the sublethal effect of AZA that also detrimental to the healthy development of the honeybee colony.

Enhanced Control of the Fungus Gnat Bradysia odoriphaga (Diptera: Sciaridae) by Co-Application of Clothianidin and Hexaflumuron.

The fungus gnat is a major pest of chive in China. Its control has been relied heavily on the application of clothianidin. Due to the intensive application, its control efficacy become reduced. The present study was intended to evaluate co-drenching of clothianidin with hexaflumuron on absorption and dissipation of clothianidin in chive plants and soils and determine the effect of such application on control efficacies. Chive production fields in Guangdong and Hubei Provinces were drenched with clothianidin alone and a mixture of clothianidin and hexaflumuron at low application rates. Concentrations of clothianidin in chive plants and soils were analyzed by HPLC. Results showed that co-application had higher control efficacies against the fungus gnat than clothianidin alone. The co-application enhanced clothianidin absorption and dissipation and extended the half-lives of clothianidin in chive. It was likely that hexaflumuron protected chive roots from larva damage, and healthy roots absorbed more clothianidin, resulting in the extension of the half-lives. Additionally, the terminal residues of clothianidin in chive after 14 days of application were lower than the maximum residue limit in chive set by the Codex Alimentarius Commission. This study for the first time documented that co-application of clothianidin and hexaflumuron improved chive plants in absorption and dissipation of clothianidin and enhanced fungus gnat control efficacies.

Examination of acephate absorption, transport, and accumulation in maize after root irrigation for Spodoptera frugiperda control.

Since the invasion of the fall armyworm moth (Spodoptera frugiperda) in China in January 2019, damage to maize crops has gradually intensified, and chemical control has become the main control measure. This study aimed to examine methods of effective pest control while monitoring the environmental impact of pesticide use. The effectiveness of S. frugiperda pest control by foliar spraying and root irrigation of maize plants with acephate was determined, and the absorption, distribution, and dissipation of acephate and methamidophos by maize were studied. Field trials showed that acephate treatment at 6000 g a.i. ha-1 was the most effective for controlling S. frugiperda. Acephate and methamidophos were absorbed from the roots, transported upward, and concentrated in the leaves, particularly new leaves. The terminal residues of acephate and methamidophos in maize grains were below detectable levels at 60 days after treatment. The results demonstrate that acephate treatment via root irrigation can more effectively control the infestation of S. frugiperda in maize than acephate treatment via foliar spraying. The translocation and distribution of acephate and methamidophos by root irrigation were more uniform, and the holding efficiency was higher than those in foliar spraying, suggesting an extended period of control efficacy. This pest control method could be utilized to reduce pesticide residues while safely and efficiently controlling S. frugiperda infestation.

Preparation of alginate-chitosan floating granules loaded with 2-methyl-4-chlorophenoxy acetic acid (MCPA) and their bioactivity on water hyacinth.

BACKGROUND: Water hyacinth (Eichhornia crassipes) is considered the most damaging aquatic weed in many countries. Chemical methods are still the primary approach to control, although this directly exposes the natural enemy of water hyacinth (water hyacinth weevil) to herbicides. In addition, spray drift can easily damage non-target plants. In this study, herbicides, natural polymer materials (chitosan and carboxymethyl chitosan), sodium alginate and natural oils (citronella oil) were used to prepare novel floating polysaccharide granules as a solution for controlling water hyacinth. RESULTS: 2-Methyl-4-chlorophenoxy acetic acid (MCPA) floating granules with a spherical structure were prepared using a MCPA-chitosan-sodium alginate-oil cross-linking and embedding method. The granules produced showed the required properties of floatation and slow controlled herbicide release. In addition, the polysaccharide granules collected around water hyacinth plants and enabled targeted release of the active herbicide ingredients onto the stems and roots of the weed, thereby stopping the herbicide from reaching non-target plants and preventing regrowth of water hyacinth. CONCLUSION: We successfully prepared highly effective MCPA-loaded floating granules, which compared with an MCPA solution, exerted greater control on water hyacinth. Concomitantly, these granules provide a solution to spray drift and ensure the safety of natural enemies of water hyacinth, which is of great significance in research on herbicide formulations.