Comparison of greenhouse and field degradation behaviour of isoprocarb, hexaflumuron and difenoconazole in Perilla frutescens

Thiamethoxam dynamics in pepper plants: Deciphering deposition and dissipation pattern across diverse planting modes and regions

To reduce the application dosage of thiamethoxam (TMX), we investigated the deposition and dissipation patterns in a pepper-planted ecosystem under different planting modes across four regions in China, namely Hainan (HN), Zhejiang (ZJ), Anhui (AH) and Hebei (HB). This study focused on the deposition and dissipation of TMX at concentrations of 63.00, 47.25, 31.50, 23.63 and 15.75 g a.i.hm-2. As the application dose increased, the deposition amount of TMX initially increased in the plants and cultivated soil, showing obvious geographic differences in four cultivation areas. Surprisingly, the initial amount of TMX deposited the pepper-cultivated greenhouse of ZJ and AH was 1.1-2.1-fold and 1.0-3.6-fold higher than that in the open field system at the same application dose, respectively. In pepper leaves, stems, fruits and soil, the dissipation exhibited rapid growth and then slowed. However, the residual concentration showed an increasing trend, followed by a subsequent decrease in the pepper roots. In different planting regions, the dissipation rate of TMX followed the order HN > ZJ > AH > HB in pepper plants and cultivated soil. In comparison to the open field, the total TMX retention rate in greenhouse was higher, indicating overall greater persistence in the greenhouse conditions. These findings reveal the deposition and dissipation characteristics of TMX within the pepper-field ecosystem, offering a significant contribution to the risk assessment of pesticides.

Dissipation patterns, residue analysis, and risk evaluation of hexaflumuron in turnip and cauliflower under Chinese growth conditions

Hexaflumuron has been globally registered over 2 decades to control the pests in brassicaceous vegetables, while data on its dissipation and residues in turnip and cauliflower is scarce. Herein, field trials were carried out at six representative experimental sites to study the dissipation behaviors and terminal residues of hexaflumuron in turnip and cauliflower. The residual amounts of hexaflumuron were extracted using a modified QuEChERS and analyzed with liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), the chronic dietary risk to Chinese populations was evaluated, and the maximum residue limit (MRL) in cauliflower, turnip tubers, and turnip leaves was calculated by the OECD MRL calculator. The single first-order kinetics model was the best-fitted kinetics model for hexaflumuron dissipation in cauliflower. The indeterminate order rate equation and first-order multi-compartment kinetic model were the best formulae for hexaflumuron dissipation in turnip leaves. The half-lives of hexaflumuron ranged from 0.686 to 1.35 and 2.41 to 6.71 days in cauliflower and turnip leaves, respectively. The terminal residues of hexaflumuron in turnip leaves of 0.321-9.59 mg/kg were much higher than in turnip tubers of < 0.01-0.708 mg/kg and cauliflower of < 0.01-1.49 mg/kg at sampling intervals of 0, 5, 7, and 10 days. The chronic dietary risk of hexaflumuron in the preharvest interval of 7 days was lower than 100% and much higher than 0.01%, indicating acceptable but nonnegligible health hazards for Chinese consumers. Therefore, MRL values of hexaflumuron were proposed as 2, 0.8, and 10 mg/kg in cauliflower, turnip tubers, and turnip leaves, respectively.

Ocean current redistributed the currently using Organoamine Pesticides in Arctic summer water

In a comprehensive study on the presence and distribution of Currently Using Organoamine Pesticides (CUOAPs) in the Arctic Ocean, this study collected and analyzed 36 surface seawater samples during the summer of 2021. The study detected 36 CUOAPs, 17 of these compounds at levels exceeding the Method Detection Limits (MDLs). Concentrations of CUOAPs ranged from 0.11 to 2.94 ng/L, exhibiting an average of 1.83 ± 0.83 ng/L. Spatial distribution analysis revealed lower CUOAP concentrations in the central Arctic Ocean, with Cycloate constituting the most abundant component (23.66 %). The investigation identified terrestrial inputs and long-range atmospheric transport as potential sources of CUOAPs in the Arctic Ocean region. The origins of individual CUOAPs appeared to be associated with application procedures and their propensity for co-occurrence at low latitudes. The study also examined the role of ocean currents in the transport and redistribution of CUOAPs in surface seawater across different regions. While ocean currents played a significant role, the influence of sea ice cover on CUOAP distribution was minimal. An ecological risk assessment analysis underscored the need for regional attention to the presence of CUOAPs in the Arctic Ocean.

Deposition and dissipation of difenoconazole in pepper and soil and its reduced application to control pepper anthracnose

The initial deposition amount, dissipation dynamics, retention rate, and field control efficacy of difenoconazole in pepper-soil system were studied with different application dosages, planting regions and patterns. The initial deposition amount of difenoconazole under the same application dosage showed the following order: fruits < cultivated soils < lower stems < upper stems < lower leaves < upper leaves, open field < greenhouse, and Changjiang < Cixi < Hefei < Langfang, respectively, which increased with increasing application dosage. The dissipation rates in leaves, stems, fruits and cultivated soils exhibited an initially fast and then slow trend, while the retention rates displayed a tendency of first increasing and then stabilizing with increasing application dosages. After 7 d of difenoconazole application, the retention rates at five concentrations were 10.3%- 39.1%, and the field efficacy mostly reached the minimum effective dose. These results suggested that difenoconazole could be reduced by 25% based on the minimum recommended dose meeting the requirements of field control efficacy for controlling pepper anthracnose.

Occurrence, vertical distribution and transport of organic amine pesticides in the seawater from the East China Sea and the South China Sea

Organic amine pesticides (OAPs) are widely used as insecticides, fungicides and herbicides in agricultural production. China is a large agricultural country, and the sprayed pesticides may impact the fragile marine environment through surface runoff. This study revealed the pollution characteristics of thirty-three OAPs in the East China Sea (ECS) and the South China Sea (SCS) and investigated their vertical variations in water columns. The ∑OAPs ranged from below method detection limits to 3.4 ng/ L, with an average value of 0.93 ng/ L. Diphenylamine and beflubutamid were the two most abundant compounds, contributing 64 % and 14 % of the ∑OAPs, respectively. The ∑OAPs in the ECS were significantly (M-W U test, p < 0.01) higher than that in the SCS, and OAPs exhibited different composition profiles. Diphenylamine was the most abundant compound in the ECS, while beflubutamid was dominant in the SCS, which may be related to industrial production (such as rubber synthesis) and agricultural activities. In the water columns, OAPs concentrations were higher in deep layers compared to that in surface seawater, which may be due to weak light and low temperature reducing the degradation of pesticides, indicating the deep ocean is a sink for OAPs. Under the dilution of seawater, the concentrations of OAPs decreased from the Pearl River Estuary to the open sea, and the South China Sea Warm Current also caused the decrease of OAPs from south to north. A preliminary risk assessment indicated that OAPs in the water pose no significant risk to aquatic organisms.

Antimicrobial Mechanism and Secondary Metabolite Profiles of Biocontrol Agent Streptomyces lydicus M01 Based on Ultra-High-Performance Liquid Chromatography Connected to a Quadrupole Time-of-Flight Mass Spectrometer Analysis and Genome Sequencing

Streptomyces lydicus was used as biopesticide for crop protection in agriculture, however, the antimicrobial mechanism remains unclear and no systematic research on the secondary metabolites of S. lydicus has been reported. In this study, the extract of S. lydicus M01 culture was used to treat plant pathogen Alternaria alternata and morphological changes in the plasma membrane and cell wall of hyphae and conidia were observed. Fluorescence microscopy combined with different dyes showed that the accumulation of reactive oxygen species and cell death were also induced. To investigate the secondary metabolites in the culture filtrate, an online detection strategy of ultra-high-performance liquid chromatography connected to a quadrupole time-of-flight mass spectrometer (UPLC-Q-TOF-MS) was used for identification. The results revealed an excess of 120 metabolites, mainly consisted of fungicides, antibacterial agents, herbicides, insecticides, and plant growth regulators, such as IAA. Among which the five dominant components were oxadixyl, chloreturon, S-metolachlor, fentrazamide, and bucarpolate. On the other hand, the complete genome of S. lydicus M01 was sequenced and a number of key function gene clusters that contribute to the biosynthesis of active secondary metabolites were revealed. This is the first systematic characterization of S. lydicus secondary metabolites, and these results offer novel and valuable evidence for a comprehensive understanding of the biocontrol agent S. lydicus and its application in agriculture.

Benzoylurea Chitin Synthesis Inhibitors

Benzoylurea chitin synthesis inhibitors are widely used in integrated pest management (IPM) and insecticide resistance management (IRM) programs due to their low toxicity to mammals and predatory insects. In the past decades, a large number of benzoylurea derivatives have been synthesized, and 15 benzoylurea chitin synthesis inhibitors have been commercialized. This review focuses on the history of commercial benzolyphenylureas (BPUs), synthetic methods, structure-activity relationships (SAR), action mechanism research, environmental behaviors, and ecotoxicology. Furthermore, their disadvantages of high risk to aquatic invertebrates and crustaceans are pointed out. Finally, we propose that the para-substituents at anilide of benzoylphenylureas should be the functional groups, and bipartite model BPU analogues are discussed in an attempt to provide new insight for future development of BPUs.

Sublethal effects of the chitin synthesis inhibitor, hexaflumuron, in the cotton mirid bug, Apolygus lucorum (Meyer-Dür)

Hexaflumuron is a type of benzoylphenylurea insecticide which is highly toxic for many insects. Sublethal doses of hexaflumuron have been shown to significantly affect insect growth and development. However, the action mechanism of hexaflumuron is not well understood. In the present study, first instar Apolygus lucorum nymphs were exposed to sublethal doses of hexaflumuron based on the estimated 120h acute LC50 valve of 20.53mg/ml. We found that exposure to sublethal hexaflumuron doses resulted in a significant increase in development time and reduced the weights of fifth instar A. lucorum nymphs. We also measured trehalose, which is a primary blood sugar in insects, and the enzyme trehalase that is involved in energy metabolism. Trehalose content in first instar nymphs significantly increased following hexaflumuron treatment while the glucose content, soluble trehalase activity and expression levels of ALTre-1 mRNA decreased significantly. However, no significant changes in membrane-bound trehalase activity and ALTre-2 mRNA expression were observed. In addition, these decreases or increases could be correlated to increases in treatment time or concentration of hexaflumuron, respectively. The present findings indicated that sublethal doses of hexaflumuron could interfere the normal carbohydrate metabolism by depressing the expression of ALTre-1 in A. lucorum, which provide valuable information on the physiology and molecular mechanisms for the toxicity of hexaflumuron.