Nano-pesticide carrier O-Carboxymethyl chitosan is indigestible in Apis cerana cerana and affects intestinal flora.

O-Carboxymethyl chitosan nanoparticles (O-CMC-NPs), which are organic pesticide carriers, have excellent application potential. Exploring the effects of O-CMC-NPs on non-target organisms, such as Apis cerana cerana, is critical for their effective application; however, such studies are limited. This study investigated the stress response of A. cerana Fabricius after O-CMC-NPs ingestion. The administration of high O-CMC-NP concentrations enhanced the activities of antioxidant and detoxifying enzymes in A. cerana, with the activity of glutathione-S-transferase increasing by 54.43 %-64.33 % after one day. The transit of O-CMC-NPs into the A. cerana midgut resulted in their deposition and adherence to the intestinal wall, as they cluster and precipitate in acidic conditions. The population of Gillianella bacteria in the middle intestine was remarkably reduced after 6 d of administration of high O-CMC-NP concentrations. Contrastingly, the abundance of Bifidobacteria and Lactobacillus in the rectum significantly increased. These results indicate that the intake of high concentrations of O-CMC-NPs causes a stress response in A. cerana and affects the relative abundance of crucial intestinal flora, which may pose a potential risk to the colony. This implies that even nanomaterials with favorable biocompatibility should be applied reasonably within a specific range to avoid adverse effects on the environment and non-target organisms in the context of large-scale research and promotion of nanomaterials.

pH-responsive λ-cyhalothrin nanopesticides for effective pest control and reduced toxicity to Harmonia axyridis.

In this study, pH-responsive LC@O-CMCS/PU nanoparticles were prepared by encapsulating λ-cyhalothrin (LC) with O-carboxymethyl chitosan (O-CMCS) to form LC/O-CMCS and then covering it with polyurethane (PU). Characterization and performance test results demonstrate that LC@O-CMCS/PU had good alkaline release properties and pesticide loading performance. Compared to commercial formulations containing large amounts of emulsifiers (e.g., emulsifiable concentrate, EC), LC@O-CMCS/PU showed better leaf-surface adhesion. On the dried pesticide-applied surfaces, the acute contact toxicity of LC@O-CMCS/PU to Harmonia axyridis (H. axyridis) was nearly 20 times lower than that of LC EC. Due to the slow-releasing property of LC@O-CMCS/PU, only 16.38 % of LC was released at 48 h in dew and effectively reduced the toxicity of dew. On the pesticide-applied leaves with dew, exposure to the LC (EC) caused 86.66 % mortality of H. axyridis larvae significantly higher than the LC@O-CMCS/PU, which was only 16.66 % lethality. Additionally, quantitative analysis demonstrated 11.33 mg/kg of λ-cyhalothrin in the dew on LC@O-CMCS/PU lower than LC (EC) with 4.54 mg/kg. In summary, LC@O-CMCS/PU effectively improves the safety of λ-cyhalothrin to H. axyridis and has great potential to be used in pest control combining natural enemies and chemical pesticides.

Eco-friendly O-carboxymethyl chitosan base chlorfenapyr nanopesticide for effective pest control and reduced toxicity to honey bees.

Enhancing pesticide selectivity is one of the important strategies to improve pesticide utilization and protect non-target organisms. Herein, a pH-controlled release carrier was prepared to enhance insecticidal activity and reduce toxicity to bees by polysaccharide materials O-carboxymethyl chitosan (O-CMCS) and crosslinker­sodium tripolyphosphate (TPP). Chlorfenapyr (CF) was encapsulated through crosslinking and self-assembled to form a stable nanopesticide (CF@O-CMCS) with a loading ratio of 5.27 %. CF@O-CMCS had excellent pH release dependency. In 36 h, only 26.39 % of the CF in the CF@O-CMCS was released at pH 5.0, whereas 95.28 % was released at pH 10.0. Treated for 48 h with 2.5 mg.ai/L, CF@O-CMCS was 73.33 % more effective at controlling Spodoptera frugiperda larvae than CF SC (Suspension), which was only 40.00 % effective. The lethal concentration 50 % (LC50) of 11.41 mg/L in CF@O-CMCS was four times lower than that of 2.71 mg/L in CF SC at 96 h, making it safer for worker bees. Additionally, CF@O-CMCS treated the gut of worker bees had considerably lower contents of chlorfenapyr and tralopyril (1.13 and 0.59 mg/kg) than CF SC (3.22 and 1.91 mg/kg) group. In consideration of its eco-friendly, enhanced bioactivity, and low toxicity to worker bees, CF@O-CMCS will have a broad application prospect in sustainable agriculture.

Rotenone encapsulated in pH-responsive alginate-based microspheres reduces toxicity to zebrafish.

Rotenone is a botanical pesticide and has long been used for control of insect pests and also as a natural piscicide for management of fish populations in many countries. Field application for pest control, however, often encounters the movement of rotenone into surface water due to spray drift or surface runoff after rainfall, which could potentially result in water pollution and unexpected death of fishes. To minimize its effect on freshwater and the problem of fish dying, one solution was to encapsulate rotenone in specific microspheres, limiting its release and reducing its toxicity since rotenone can be quickly degraded under sunlight. In this study, pH-responsive alginate-based microspheres were synthesized to encapsulating rotenone, which were designated as rotenone beads. The rotenone beads, along with alginate beads (devoid of rotenone) were characterized and evaluated for their responses to pH and effects on zebrafish. Results showed that the microspheres had high loading efficiency (4.41%, w/w) for rotenone, and rotenone beads well responded to solution pH levels. The cumulative release rates of rotenone from the beads were 27.91%, 42.72%, and 90.24% at pH 5.5, 7.0, and 9.0, respectively. Under acidic conditions, the rotenone release rate was lower due to hydrogen bonding. On the contrary, rotenone became more quickly released at the high pH due to intermolecular repulsion. The toxicity of rotenone beads to zebrafish and fish embryos at a pH of 5.5 was reduced by 2- and 4-fold than chemical rotenone. Since pH levels in most freshwater lakes, ponds, and streams vary from 6 to 8, rotenone release from the beads in such freshwater could be limited. Thus, the synthesized rotenone beads could be relatively safely used for pest control with limited effects on freshwater fishers.

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.

Fabrication of sulfoxaflor-loaded natural polysaccharide floating hydrogel microspheres against Nilaparvata lugens (Stal) in rice fields.

BACKGROUND: Nilaparvata lugens (Stal) nymphs and adults aggregate and feed on leaf sheaths at the base of rice plants. It is difficult to apply traditional spray treatments directly onto the plant stems due to the blocking agent produced by leaves. Further, spiders and mirids, the natural enemies of N. lugens (Stal), are directly exposed to the chemicals during spraying. Sulfoxaflor-loaded natural polysaccharide microspheres with good performance were developed and tested in rice fields. The absorption, distribution, and dissipation of sulfoxaflor in rice plants, soil, and water were examined. RESULTS: Sulfoxaflor-loaded natural polysaccharide microspheres were prepared through physical embedding and ionic crosslinking, using citronellol as an oil phase to provide floatation. The sustained release of sulfoxaflor was achieved through swelling and dissolution, indicating that these structures could effectively control pesticide release. Field experiments showed that these microspheres were able to float in water and gather around the stem of rice plants and that their insecticidal effect was remarkably improved compared to that achieved using the suspension concentrate. Results also showed that the residual content of stems following treatment with sulfoxaflor-loaded natural polysaccharide microspheres reached 0.331 mg kg-1 , but was reduced in other parts of the plant. CONCLUSION: In the present study, sulfoxaflor-loaded natural polysaccharide microspheres with optimized properties were successfully prepared. These microspheres produced a better control effect on N. lugens (Stal) compared to the use of the sulfoxaflor suspension concentrate. Their application may help promote the scientific control of target pests in rice fields. © 2020 Society of Chemical Industry.

Different lethal treatments induce changes in piperidine (1,1'-(1,2-ethanediyl)bis-) in the epidermal compounds of red imported fire ants and affect corpse-removal behavior.

Corpse-removal behavior of the red imported fire ant (RIFA) and the effects of lethal substances on RIFA signal communication were investigated in this study. The RIFA corpses, obtained through freezing, ether, 0.25 mg/L thiamethoxam, and starvation to death treatments, and naturally dead red fire ants were subjected to gas chromatography-mass spectrometry to identify the cuticular hydrocarbon profiles that had an effect on the corpse-removal behavior. The results showed that lethal toxic substances altered the epidermal compounds of RIFA and affected their corpse-removal behavior. Lethal toxic substances increased the number of worker touches with corpses and identification time of corpses. In addition, the content of piperidine (1,1'-(1,2-ethanediyl)bis-) on the surface of the corpse was different following the various treatments. Contamination with toxic substances resulted in the increased secretion of piperidine and led to increased identification time of corpses, number of touch with corpses, and total time for removal of corpses. Piperidine content was higher under conditions of natural death (4.67 ± 0.55%) and with thiamethoxam (10.43 ± 0.78%), freezing (0.83 ± 0.25%), and ether treatment (12.50 ± 0.70%) than under starvation treatment (0). The higher content of piperidine led to a longer number of touches with corpses and identification time. Piperidine compounds may be an element in warning information, which could affect the occurrence of different corpse-removal behaviors.