Seed treatment with chlorantraniliprole and carbaryl mixture for managing fall armyworm on maize: systemic synergism, control efficiency and synergistic mechanism.

BACKGROUND: Fall armyworm (Spodoptera frugiperda) is one of the major invasive pests in China, and has been widely controlled by labor-intensive foliar sprays of agrochemicals in maize (Zea mays L.). RESULTS: Systemic bioassay showed that mixtures of chlorantraniliprole (Chlor) and carbaryl (Carb) had dramatically synergistic effect on toxicity to S. frugiperda. Particularly, a mixture of Chlor with Carb at a mass ratio of 2:1 (MCC) exhibited the highest toxicity to S. frugiperda. Therefore, seed treatment of Chlor mixed with Carb was studied as a simple, accurate, efficient and low-cost control technology. Our results showed that MCC treatment shortened the median lethal time and 90% lethal time to S. frugiperda compared to Chlor- and Carb-alone treatments. Meanwhile, smaller leaf consumption by S. frugiperda was recorded under MCC treatment compared to Chlor- and Carb-alone treatments. In field trial, maize-seed treatment with MCC showed efficacy up to 39 days post-emergence in preventing S. frugiperda foliar damage at a low infestation pressure. Moreover, chemical quantification by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) showed that Chlor residues were more absorbed and concentrated in maize leaves of MCC treatment, compared to that of Chlor-alone treatment. CONCLUSION: These results suggested that seed treatment with MCC can be applied to increase the control efficacy and reduce the cost of Chlor-alone treatment for controlling S. frugiperda. The present study provided evidence of an enhanced translocation and accumulation of Chlor residues in maize leaves under MCC treatment, which likely contributed to a synergistic effect against S. frugiperda. © 2022 Society of Chemical Industry.

Factors Underlying the Prevalence of Pythium Infection of Corn Seeds Following Seed Treatment Application of Tebuconazole.

Microbial communities are essential for soil health, but fungicide application may have significant effects on their structure. It is difficult to predict whether nontarget pathogens of applied fungicides in the soil will cause crop damage. Tebuconazole is a triazole fungicide that can be used as a seed treatment and, thereby, introduced to the soil. However, seed-applied tebuconazole has a potential risk of causing poor emergence of corn (Zea mays) seedlings. Using soil with a history of poor corn seedling emergence, we demonstrate through TA cloning and isolation that the poor emergence of corn seedlings from tebuconazole-coated corn seeds was primarily because of infection by surviving soil pathogens, specifically Pythium species that are not targeted by tebuconazole, rather than the phytotoxic effects of tebuconazole. Bioassay tests on tebuconazole-amended media showed that tebuconazole can suppress soil fungi while allowing Pythium to grow. Pythium species primarily contributing to the corn seed rot were more pathogenic at cooler temperatures. Furthermore, the nontarget biocontrol agent of Trichoderma spp. was strongly inhibited by tebuconazole. Taken together, the nontarget effects of tebuconazole are likely not significant under favorable plant growing conditions but are considerable because of low-temperature stress.

Design, synthesis and fungicidal activity of N-substituted benzoyl-1,2,3,4-tetrahydroquinolyl-1-carboxamide.

To find a new lead compound with high biological activity, a series of N-substituted benzoyl-1,2,3,4-tetrahydroquinolyl-1-carboxamide were designed using linking active substructures method. The target compounds were synthesized from substituted benzoic acid by four steps and their structures were confirmed by (1)H NMR, IR spectrum and elemental analysis. The in vitro bioassay results indicated that some target compounds exhibited excellent fungicidal activities, and the position of the substituents played an important role in fungicidal activities. Especially, compound 5n, exhibited better fungicidal activities than the commercial fungicide flutolanil against two tested fungi Valsa mali and Sclerotinia sclerotiorum, with EC50 values of 3.44 and 2.63mg/L, respectively. And it also displayed good in vivo fungicidal activity against S. sclerotiorum with the EC50 value of 29.52mg/L.

Molecular cloning, characterization and expression profiling of a ryanodine receptor gene in Asian corn borer, Ostrinia furnacalis (Guenée).

Ryanodine receptor (RyR) Ca(2+) release channel is the target of diamide insecticides, which show selective insecticidal activity against lepidopterous insects. To study the molecular mechanisms underlying the species-specific action of diamide insecticides, we have cloned and characterized the entire cDNA sequence of RyR from Ostrinia furnacalis (named as OfRyR). The OfRyR mRNA has an Open Reading Frame of 15324 bp nucleotides and encodes a 5108 amino acid polypeptide that displays 79-97% identity with other insects RyR proteins and shows the greatest identity with Cnaphalocrocis medinalis RyR (97%). Quantitative real-time PCR showed that the OfRyR was expressed at the lowest level in egg and the highest level in adult. The relative expression level of OfRyR in first, third and fifth-instar larva were 1.28, 1.19 and 1.99 times of that in egg. Moreover, two alternative splicing sites were identified in the OfRyR gene. One pair of mutually exclusive exons (a/b) were present in the central part of the predicted SPRY domain, and an optional exon (c) was located between the third and fourth RyR domains. Diagnostic PCR demonstrated that exons a and b existed in all developmental stages of OfRyR cDNA, but exon c was not detected in the egg cDNA. And the usage frequencies of these exons showed a significant difference between different developmental stages. These results provided the crucial basis for the functional expression of OfRyR and for the discovery of compound with potentially selective insect activtity.

Modulation of the expression of ryanodine receptor mRNA from Plutella xylostella as a result of diamide insecticide application.

Ryanodine receptors (RyRs), members of the largest family of calcium channel proteins, have been studied because of their key roles in calcium signalling within cells. With the development of diamide insecticides that exhibit a novel mode of action on the RyRs from Lepidoptera, research on insect RyRs has become more attractive in the field of plant protection. To enhance our understanding of the effects of diamides on RyRs, we cloned the Plutella xylostella RyR gene (Px-RyR), which is the most serious pest of Brassicaceae plants throughout the world. Furthermore, we investigated the modulation of the expression of Px-RyR as a result of the application of diamide insecticides. The full-length cDNAs of Px-RyR contain an open reading frame (ORF) of 15,372bp with a predicted protein consisting of 5123 amino acids. Px-RyR possesses a high level of overall amino acid homology with other isoforms (77-92% identity with insect isoforms and 45-47% identity with vertebrate isoforms). The weight of Px. gradually decreased as the concentration of the diamides increased. However, the relative expression levels of the RyRs from larvae were dependent on the insecticide concentration and gradually increased with increasing insecticide concentrations.

The fungicidal terpenoids and essential oil from Litsea cubeba in Tibet.

A new C9 monoterpenoid acid (litseacubebic acid, 1) and a known monoterpene lactone (6R)-3,7-dimethyl-7-hydroxy-2-octen-6-olide (2), along with three known compounds--vanillic acid (3), trans-3,4,5-trimethoxylcinnamyl alcohol (4), and oxonantenine (5)--were isolated with bioassay-guided purification from the fruit extract of Litsea cubeba collected in Tibet. The structure of 1 was elucidated by MS, ¹H-NMR, ¹³C-NMR, COSY, HSQC, HMBC, NOE spectral data as 2,6-dimethyl-6-hydroxy-2E,4E-hepta-2,4-diene acid. Additionally 33 compounds were identified from the essential oil of L. cubeba. The preliminary bioassay results showed that 1 and 2 have good fungicidal activities against Sclerotinia sclerotiorum, Thanatephorus cucumeris, Pseudocer-cospora musae and Colletotrichum gloeosporioides at the concentration of 588 and 272 µM, and the essential oil has good fungicidal activities against T. cucumeris and S. sclerotiorum, with IC50 values of 115.58 and 151.25 µg/mL, repectively.

Recent progress of highly efficient in vivo biological screening for novel agrochemicals in China.

This paper describes the recent progress of in vivo biological screening for pesticides in China. According to the criteria, including the severity of damage caused by pests and the economic value of the crops, the investigated insects, pathogens, herbs and other species in the agricultural field were selected as the main screening targets for pesticides. Corresponding in vivo microscreening methods have been established and applied in the pesticide screening procedure, which has higher reproducibility, a shorter time and greater efficiency that offset the drawbacks of conventional methods for pesticide screening.