Journal of Pesticide Science最新文献

Widespread pesticide use for decades has caused environmental damage, biodiversity loss, serious human and animal health problems, and resistance to insecticides. Innovative strategies are needed to reduce treatment doses in pest management and to overcome insecticide resistance. In the present study, combinations of indoxacarb, an oxadiazine insecticide, with sublethal concentrations of deltamethrin encapsulated in lipid nanocapsules, have been tested on the crop pest Acyrthosiphon pisum. In vivo toxicological tests on A. pisum larvae have shown a synergistic effect of nanoencapsulated deltamethrin with a low dose of indoxacarb. Furthermore, the stability of deltamethrin nanoparticles has been demonstrated in vitro under different mimicking environmental conditions. In parallel, the integrity and stability of lipid nanoparticles in the digestive system of aphid larvae over time have been observed by Förster Resonance Energy Transfer (FRET) imaging. Thus, the deltamethrin nanocapsules/indoxacarb synergistic association is promising for the development of future formulations against pest insects to reduce insecticide doses.

The fungicidal properties of a new fungicide, isofetamid, were examined to assess its antifungal spectrum, mode of action, and effects on the infection process of Botrytis cinerea. Additionally, we investigated its fungicidal activity against isolates of B. cinerea resistant to existing fungicides. In mycelial growth inhibition tests, isofetamid exhibited excellent fungicidal activity against ascomycetes but showed no activity against basidiomycetes and oomycetes. Respiratory enzyme assay using mitochondria revealed that isofetamid inhibited succinate dehydrogenase activity prepared from B. cinerea and other ascomycetes fungi used in the study. On the other hand, the activity of mitochondria prepared from Pythium, potato and rat were not inhibited. Isofetamid inhibited also many stages of the infection processes in B. cinerea. Furthermore, it exhibited high fungicidal activity against B. cinerea isolates that were resistant to existing fungicides.

Rice false smut (RFS) caused by Ustilaginoidea virens is widely distributed in major rice-producing regions. Previous studies have shown that treating RFS with chelerythrine can decrease the germination of fungus spores by 86.7% and induce fungal cell apoptosis. In the present study, the effects of chelerythrine on the metabolism of U. virens explored using metabolomics and analyses of differentially accumulated metabolites and altered metabolic pathways. The top 15 metabolites in random forest analysis were significantly different between groups. In positive ion mode, purine, phenylalanine metabolism, phenylalanine, tyrosine, tryptophan biosynthesis, pyrimidine metabolism, and nitrogen metabolism were dominant. Alanine, aspartate, glutamate metabolism, and phenylalanine metabolism were enriched in negative ion mode. Differentially expressed genes and altered metabolic pathways of U. virens were effected by chelerythrine. The findings support future research on the prevention and treatment of RFS by chelerythrine and provide a theoretical basis for targeted drug delivery.

Using PCR-Restriction Fragment Length Polymorphism (RFLP) with mitochondrial cytochrome c oxidase subunit I sequences, we examined the reproductive modes of female adults of Thrips tabaci collected at 54 sites across Japan. Results showed the presence of heteroplasmic insects harboring mitochondria associated with arrhenotoky and thelytoky. Using the insects, we also applied PCR-RFLP to examine the genotypes for the amino acid mutation (T929I) site involved in pyrethroid resistance. Findings showed the presence of thelytokous heterozygotes under the circumstance that most arrhenotokous insects are resistant homozygotes, and many thelytokous insects are susceptible homozygotes. These results suggest that, in the field, genetic exchange occurs between insects through of both reproductive modes. A survey of the genotypes for the other amino acid mutations using nucleotide sequencing showed a decline of insects with an M918T and L1014F pair and an increase of insects with M918L. These results suggest the evolutional progression of amino acid mutations associated with pyrethroid resistance in T. tabaci.

Previously, we found that 5-(2,6-dimethoxybenzoylamino)-3-phenylisoxazoles (IOXs) inhibit chitin synthesis in the cultured integument of Chilo suppressalis. In this study, IOXs with various substituents at the para-position of the 3-phenyl ring were synthesized, and the concentrations required to inhibit chitin synthesis to 50% (IC₅₀) were determined for all compounds. The introduction of halogens—such as F, Cl, and Br—and small alkyls—such as Me, Et, Pr, and n-Bu—at the 3-phenyl ring slightly enhanced the activity. However, the activity decreased drastically with the introduction of NO₂, CF₃, and t-Bu. The quantitative analysis of the substituent effect at the 3-phenyl ring on chitin-synthesis inhibition using the Hansch-Fujita method showed that the hydrophobic substituent with the optimum value was favored for the activity, but the bulky substituent in terms of E_s was detrimental to the activity.

Nitenpyram (neonicotinoid insecticide) is commonly used for crop protection from pests. Currently, due to its widespread use, the nitenpyram accumulation in the environment is anticipated to be high. Hence, the removal of nitenpyram residue from the environment is essential. However, the biodegradation of nitenpyram by endophytes is still unreported. Therefore, we aimed to isolate and identify a bacterial strain capable of degrading nitenpyram. We isolated approximately 300 endophytic strains from Brassica rapa var. perviridis that had been exposed to different neonicotinoid insecticides. After 14 days of incubation, a bacterial strain, NIT-2, with nitenpyram degradation capability (approximately 65%) was found. Via 16S rRNA gene sequencing, the strain was identified as Bacillus thuringiensis. In addition, metabolites, 2-[N-(6-chloro-3-pyridylmethyl)-N-ethyl]amino-2-methyliminoacetic acid, N-(6-chloro-3-pyridilmethyl)-N-ethyl-N-methylformamidine (CPMF), and N-(6-chloro-3-pyridilmethyl)-N-ethylformamide (CPF), were identified during the degradation. Moreover, CPMF and CPF were further degraded 71% and 18%, respectively by NIT-2. Thus, B. thuringiensis strain NIT-2 is the first reported endophytic bacterium capable of degrading nitenpyram.

Dimesulfazet can control annual and perennial sedges in rice paddies. Here we assessed its mode of action. We performed a phenotype assay of Arabidopsis, conducted a metabolomic analysis of Echinochloa crus-galli, and analyzed the endogenous concentration of very long-chain fatty acids (VLCFAs) in Schoenoplectiella juncoides. Dimesulfazet treatment caused curling and greening symptoms in the leaves and fiddlehead-like symptoms in the inflorescences of Arabidopsis. These symptoms were visually indistinguishable from those caused by flufenacet and benfuresate, which belong to Herbicide Resistance Action Committee (HRAC) Group 15. We performed GC-MS/MS analysis of primary metabolites and LC-MS analysis of lipids in the herbicide-treated E. crus-galli, followed by Orthogonal Partial Least Squares Discriminant Analysis clustering. The results showed that dimesulfazet belongs to the HRAC Group 15 cluster. The endogenous concentrations of C24:0, C26:0, and C28:0 decreased in dimesulfazet-treated plants as compared to those in the control. Overall, the mode of action of dimesulfazet involves the inhibition of VLCFA biosynthesis.

The matrix effects (ME) in simultaneous analysis of pesticide residue using liquid chromatography-tandem mass spectrometry (LC-MS/MS) were evaluated by comparing the slopes of matrix-matched and reagent-only calibrations of four types of vegetable samples. Both the sampling and measurement variances of the ME were also determined using one-way analysis of variance. Substantial ion suppression (ME<−20%) was observed in komatsuna, spinach, and tomato when a modified Japanese official method was implemented. The ME magnitude varied significantly due to sample variability for some pesticides, but it varied by no more than 4% as a result of analytical procedure variance. This study also showed that the addition of stable isotope-labeled internal standards at low concentrations improved the recovery of pesticides from samples at various residue levels. The findings of this study highlight the importance and practical application of internal standards and the matrix-matched calibration method in residue analysis using LC-MS/MS.

A simple fluorescent “on-off” system that can be utilized for the selective identification and determination of paraquat (PQ) is presented herein. ¹H NMR spectroscopic data indicated that in aqueous solution the alkaloid palmatine can be partially encapsulated within the cucurbit[7]uril (Q[7]) cavity, whereby a stable 1 : 1 host–guest inclusion complex is formed. Other characterization techniques including mass spectrometry, UV-Vis and fluorescence spectroscopy also provided further evidence, and the host-guest inclusion complex was found to exhibit reasonable fluorescence intensity. It is noteworthy that the addition of PQ resulted in quenching the fluorescence of the host-guest inclusion complex, whereas the presence of 12 other pesticides did not significantly affect the fluorescence intensity. Given the linear relationship between the intensity of the fluorescence and the PQ concentration, the PQ concentration in aqueous solution was easily detected. Thus, a new method for identifying and determining the fluorescence quenching of PQ has been developed in this work.

The degradation behavior of mandestrobin (1) was investigated in aerobic aquatic water–sediment systems exposed to continuous artificial sunlight (λ>290 nm). [¹⁴C]mandestrobin uniformly labeled at the phenoxy or benzyl ring was individually applied to the overlying water of the system at a rate equivalent to 262.5 g a.i./ha. The transformation of 1 was mainly proceeded via photoinduced bond cleavage at the benzyl phenyl ether and the subsequent rearrangement reaction. Interestingly, some of the photodegradates and microbial metabolites of 1 observed in the aquatic photodegradation and water–sediment (dark) studies, respectively, were never detected. Furthermore, the observed photoproducts were less formed and were steadily degraded or metabolized to carbon dioxide or strongly adsorbed to bottom sediment. The fate of 1 and its degradates in illuminated water–sediment systems was considered to reflect realistic conditions more precisely, as it accounts for various effects attributed to sunlight.