Pesticide Biochemistry and Physiology最新文献

Isoxazoline insecticides have shown broad-spectrum insecticidal activity against a variety of insect pests. However, the high toxicity of isoxazoline compounds towards honeybees restricts their application in crop protection. To mitigate this issue, a series of isoxazoline derivatives containing 2-phenyloxazoline were designed and synthesized. Bioassays revealed that several compounds exhibited promising insecticidal activities against Plutella xylostella, with G28 showing particularly excellent insecticidal activity, reflected by an LC₅₀ value of 0.675 mg/L, which is comparable to that of fluxametamide (LC₅₀ = 0.593 mg/L). Furthermore, G28 also exhibited effective insecticidal activity against Solenopsis invicta. Importantly, bee toxicity experiments indicated that G28 had significantly lower acute oral toxicity (LD₅₀ = 2.866 μg/adult) compared to fluxametamide (LD₅₀ = 1.083 μg/adult) and fluralaner (LD₅₀ = 0.022 μg/adult), positioning it as a promising candidate with reduced toxicity to bees. Theoretical simulation further elucidated the reasons for the selective differences in the ability of isoxazoline to achieve higher insecticidal activity while maintaining lower bee toxicity. This research suggests that isoxazoline compounds containing 2-phenyloxazoline group hold potential as new insecticide candidates and offers insights into the development of novel isoxazoline insecticides with both high efficacy and environmental safety.

Bombyx mori is an insect species of great economic importance, and its silk gland is a vital organ for the synthesis and secretion of silk protein. However, long-term artificial domestication of B. mori has resulted in high sensitivity to chemical toxins, especially insecticides. Cyantraniliprole (Cya), a second-generation ryanodine receptor modulator insecticide, is widely utilized in agriculture for pest control. In this study, the impact of Cya toxicity on the development of silk glands in the 5th instar larvae of B. mori was assessed using Cya LC₅, LC₁₀ and LC₂₀, as well as a starvation treatment group for comparison. Short-term exposure (24 h) to different concentrations of Cya resulted in delayed development of silk glands in B. mori. Meanwhile, the body weight, silk gland weight, silk gland index and cocoon quality were significantly reduced in a concentration-dependent manner, except for the Cya LC₅ treatment. Histopathological and ultrastructural analysis revealed that Cya LC₁₀ induced disruption of the nuclear membrane and endoplasmic reticulum in the posterior silk gland (PSG) cells, leading to the formation of intracellular vacuoles. Transcriptome sequencing of PSGs identified 2152 genes that were differentially expressed after exposure to Cya LC₁₀, with 1153 down-regulated genes and 999 up-regulated genes. All differentially expressed genes were subjected to functional annotation using gene ontology and Kyoto encyclopedia of genes and genomes database, and it was found that protein synthesis-related pathways were significantly enriched, with the majority of genes being down-regulated. Furthermore, the transcription levels of genes involved in “protein processing in endoplasmic reticulum”, “protein export”, “proteasome” and “DNA replication” were quantified using qRT-PCR. Our findings suggested that short-term exposure to Cya LC₁₀ resulted in disruption of DNA replication, as well as protein transport, processing and hydrolysis in the PSG cells of B. mori. The results of this study provide a theoretical foundation for the safe utilization of Cya in sericulture production.

The black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae), is an important agricultural pest. Phoxim is an organophosphate insecticide that has been widely used to control A. ipsilon. The extensive application of phoxim has resulted in a reduction in phoxim susceptibility in A. ipsilon. However, the molecular mechanisms underlying phoxim tolerance in A. ipsilon remain unclear. In this work, we report the involvement of AiGSTz1, a zeta class glutathione S-transferase, in phoxim tolerance in A. ipsilon. Exposure to a sublethal concentration (LC₅₀) of phoxim dramatically upregulated the transcription level of the AiGSTz1 gene in A. ipsilon larvae, and this upregulation might be caused by phoxim-induced oxidative stress. The recombinant AiGSTz1 protein expressed in Escherichia coli was able to metabolize phoxim. Furthermore, AiGSTz1 displayed antioxidant activity to protect against oxidative stress. Knockdown of AiGSTz1 by RNA interference significantly increased the mortality rate of A. ipsilon larvae in response to phoxim. In addition, the transcription factor AiCncC can bind to the cap ‘n’ collar isoform C: muscle aponeurosis fibromatosis (CncC:Maf) binding site in the putative promoter of the AiGSTz1 gene. Silencing of AiCncC resulted in a dramatic downregulation of AiGSTz1. These results indicated that AiGSTz1 is involved in phoxim tolerance and is potentially regulated by AiCncC. These findings provide valuable insights into the defense mechanisms used by A. ipsilon against phoxim.

RNA interference (RNAi) is an effective pest management strategy through silencing the crucial genes in target organisms. However, the effectiveness of targeting a single gene is often limited by the silencing efficiency due to tissue or developmental stage-specific gene expression. Moreover, multiple pests often infest the same crop simultaneously under current ecological conditions. Therefore, a combined strategy of “targeting multiple genes” and “controlling multiple pests” is expected to yield better management results. In this study, homologous genes from two globally sap-sucking pests, the peach aphid (Myzus persicae) and the whitefly (Bemisia tabaci), were screened on a genome-wide scale. Subsequently, RNAi bioassays showed silencing the genes (MpAbd-A, MpH3, MpRpL27a, and MpScr) exhibited high mortalities in both species, which were further selected for designing fusion dsRNAs. These fusion dsRNAs resulted in higher mortalities in both pests than single gene silencing and posed a minimal off-target risk to the predator ladybeetle (Propylaea japonica) based on the sequence analysis. Finally, the tobacco plants expressing the fusion dsRNAs through virus-induced gene silencing (VIGS) technology enhanced the resistance to both pests. In conclusion, this study proposes a novel RNAi-based approach for managing two sap-sucking pests simultaneously.

Rhamnolipids (RLs) are amphiphilic compounds of bacterial origin that offer a broad range of potential applications as biosurfactants in industry and agriculture. They are reported to be active against different plant pests and pathogens and thus are considered promising candidates for nature-derived plant protection agents. However, as these glycolipids are structurally diverse, little is known about their exact mode of action and, in particular, the relation between molecular structure and biological activity against plant pests and pathogens.

Engineering the synthesis pathway in recombinant Pseudomonas putida strains in combination with advanced HPLC techniques allowed us to separately analyze the activities of mixtures of pure mono-RLs (mRLs) and of pure di-RL (dRLs), as well as the activity of single congeners. In a model system with the plant Arabidopsis thaliana and the plant-parasitic nematode (PPN) Heterodera schachtii we demonstrate that RLs can significantly reduce infection, whereas their impact on the host plant varied depending on their molecular structure. While mRLs reduced plant growth even at a low concentration, dRLs showed a neutral to beneficial impact on plant development. Treating plants with dRLs triggered an increased reactive oxygen species (ROS) production, indicating the activation of stress-response signaling and possibly plant defense. Pretreatment of plants with mRLs or dRLs prior to application of flagellin (flg22), a known ROS inducer, further increased the ROS response to flg22. While dRLs stimulated an elevated flg22-induced ROS peak, a pretreatment with mRLs resulted in a prolonged synthesis of ROS indicating a generally elevated stress level. Neither mRLs nor dRLs induced the expression of plant defense marker genes of salicylic acid, jasmonic acid, and ethylene pathways.

Detailed studies on dRLs revealed that even high concentrations up to 755 ppm of these molecules have no lethal impact on H. schachtii infective juveniles. Infection assays with individual dRL congeners showed that the C10-C8 acyl chained dRL was the only congener without effect, while dRLs with C10-C12 and C10-C12:1 acyl chains were most efficient in reducing nematode infection even at concentrations below 2 ppm. As determined by phenotyping and ROS measurements, A. thaliana reacted more sensitive to long-chained dRLs in a concentration-dependent manner.

Our experiments show a clear structure-activity relation for the effect of RLs on plants. In conclusion, functional assessment and analysis of the mode of action of RLs in plants and other organisms require careful consideration of their molecular structure and composition.

Eleusine indica is one of the most troublesome weeds in farmland worldwide, especially in Citrus Orchard of China. Glufosinate, as an efficient non-selective broad-spectrum herbicide, has been widely utilized for the control of E. indica in Citrus Orchard. The E. indica resistant population (R) was collected from a Citrus Orchard in Yichang City in Hubei province, China. Bioassay experiments showed that the R plants exhibited 3-fold resistance to glufosinate compared with the E. indica susceptible population (S). No known glutamine synthetase (GS) gene mutation associated with glufosinate resistance was found in R plants. And there was also no significant difference in GS activity between R and S plants. Those results indicated that the resistance to glufosinate in R did not involve target-site resistance. However, glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBD-Cl) plus glufosinate gave a better control of R plants compared with glufosinate treatment alone. Moreover, both before and after glufosinate treatment, the GST activity in R plants was significantly higher than that in S plants. By RNA-seq, the expression of GSTU6 and GST4 up-regulated in R plants relative to S plants with or without glufosinate treatment. They were also significantly up-regulated expression in E. indica field resistant populations compared with S population. In summary, the study elucidated that R plants developed metabolic resistance to glufosinate involving GST. And GSTU6 and GST4 genes may play an important role in this glufosinate metabolic resistance. The research results provide a theoretical basis for a deeper understanding of resistance mechanism to glufosinate in E. indica.

Riptortus pedestris (Hemiptera: Alydidae), a common agricultural pest, is the major causative agent of “soybean staygreen.” However, the interactions between chemosensory proteins (CSPs) in R. pedestris and host plant volatiles have yet to be comprehensively studied. In this study, we performed real-time fluorescence quantitative polymerase chain reaction (PCR) to analyze the antennal expression of RpedCSP22 and subsequently analyzed the interactions between 21 soybean volatiles, five aggregation pheromones, and RpedCSP22 protein in vitro using a protein expression system, molecular docking, site-directed mutagenesis, and fluorescence competitive binding experiments. The RpedCSP22 protein showed binding affinity to three soybean volatiles (benzaldehyde, 4-ethylbenzaldehyde, and 1-octene-3-ol), with optimal binding observed under neutral pH conditions, and lost binding ability after site-directed mutagenesis. In subsequent RNA interference (RNAi) studies, gene silencing was more than 90 %, and in silenced insects, electroantennographic responses were reduced by more than 75 % compared to non-silenced insects. Moreover, Y-tube olfactory behavioral assessments revealed that the attraction of R. pedestris to the three soybean volatiles was significantly attenuated. These findings suggest that RpedCSP22 plays an important role in the recognition of host plant volatiles by R. pedestris andprovides a theoretical basis for the development of novel inhibitors targeting pest behavior.

The interaction between environmental factors affecting honey bees is of growing concern due to their potential synergistic effects on bee health. Our study investigated the interactive impact of Varroa destructor and chlorothalonil on workers' survival, fat body morphology, and the expression of gene associated with detoxification, immunity, and nutrition metabolism during their adult stage. We found that both chlorothalonil and V. destructor significantly decreased workers' survival rates, with a synergistic effect observed when bees were exposed to both stressors simultaneously. Morphological analysis of fat body revealed significant alterations in trophocytes, particularly a reduction in vacuoles and granules after Day 12, coinciding with the transition of the bees from nursing to other in-hive work tasks. Gene expression analysis showed significant changes in detoxification, immunity, and nutrition metabolism over time. Detoxification genes, such as CYP9Q2, CYP9Q3, and GST-D1, were downregulated in response to stressor exposure, indicating a potential impairment in detoxification processes. Immune-related genes, including defensin-1, Dorsal-1, and Kayak, exhibited an initially upregulation followed by varied expression patterns, suggesting a complex immune response to stressors. Nutrition metabolism genes, such as hex 70a, AmIlp2, VGMC, AmFABP, and AmPTL, displayed dynamic expression changes, reflecting alterations in nutrient utilization and energy metabolism in response to stressors. Overall, these findings highlight the interactive and dynamic effects of environmental stressor on honey bees, providing insights into the mechanisms underlying honey bee decline. These results emphasize the need to consider the interactions between multiple stressors in honey bee research and to develop management strategies to mitigate their adverse effects on bee populations.

Plant essential oils (EOs)-based acaricides have been recognized as environmentally-friendly alternatives to synthetic acaricides because of their low toxicity against non-target species. Despite this, there are knowledge gaps regarding the toxicity mechanisms of plant EOs against non-target species. Here, the toxicology and enzymatic mechanism of Citrus reticulata and Citrus lemon EOs were evaluated against the vector pest, Haemaphysalis longicornis, and non-target ladybird beetle, Harmonia axyridis. Both EOs were mainly composed of d-Limonene, followed by β-Myrcene and γ-Terpinene in C. reticulata, and (−)-β-Pinene and γ-Terpinene in C. lemon. Citrus reticulata and C. lemon EOs were toxic to Hae. longicornis, with 50 % lethal concentration (LC₅₀) values estimated at 0.43 and 0.98 μL/mL via nymphal immersion test, and 42.52 and 46.38 μL/mL via spray application, respectively. Among the constituents tested, β-Myrcene was the most effective, with LC₅₀ values of 0.17 and 47.87 μL/mL via immersion and spray treatment, respectively. A significant mortality of non-target Har. axyridis was found when treated by the EOs at concentrations two times greater than LC₅₀ estimated against H. longicornis. The biochemical assay revealed that the EOs induced changes in the antioxidant enzyme activity of superoxide dismutases, catalase, and glutathione peroxidase in Hae. longicornis and Har. axyridis. The results demonstrated the acaricidal potential of citrus EOs and their major constituents for tick control, revealed the risk of the EOs to non-target species, and provided relevant insights into the mechanisms underlying their toxicity.

The invasive golden apple snail Pomacea canaliculata is one of the devastating threats to aquatic ecosystems and wetland agriculture worldwide. Macrolides from microbes display various advantages over other compounds in controlling snails. However, emergence of antibiotic-resistant phenotypes against certain macrolides in the field appeals for exploring more effectively molluscicidal macrolides. Here, two borrelidins, borrelidin BN1 and BN2, from the extract of a Streptomyces strain fermentation were evaluated for molluscicidal potential against P. canaliculata using both immersion and contact bioassay methods. Borrelidin BN1 (borrelidin A) presented a significant molluscicidal activity comparable to the chemical pesticide metaldehyde, and had a much lower median lethal concentration value (LC₅₀, 522.984 μg·ml⁻¹) than avermectin B1 at 72 h of contact-killing treatment. Snail growth was inhibited by borrelidin BN1 more than by metaldehyde at sublethal concentrations, consistent with responses of key biochemical parameters. Exposure to borrelidin BN1 decreased the activity of acetylcholinesterase (AChE), glutathione S-transferase (GST), aspartate aminotransferase (AST), alanine aminotransferase (ALT) as well as the levels of energy reserves and sex steroids in snail tissues, while increased the activity of superoxide dismutase (SOD), catalase (CAT), lactate dehydrogenase (LDH) and the level of lipid peroxidation (LPO). Further application assay confirmed that borrelidin BN1 protected crop plant Zizania latifolia from P. canaliculata damage via suppressing snail population density. These findings suggest great potential of borrelidin BN1 as a molluscicide. Additionally, its higher activity than the stereoisomeric borrelidin BN2 (borrelidin F) implied better molluscicidal borrelidins could be acquired through structural optimization.