Xiaojing Yan

Effects of cycloxaprid, a novel cis-nitromethylene neonicotinoid insecticide, on the feeding behaviour of Sitobion avenae.

BACKGROUND Cycloxaprid with cis-configuration is a novel neonicotinoid insecticide, developed in China, that has good industrialisation prospects for its high activity against imidacloprid-resistant pests. Studies were carried out to investigate the biological activity of cycloxaprid and its effect on the feeding behaviour of Sitobion avenae. RESULTS The results demonstrated that cycloxaprid had good contact and root-systemic activity. The electrical penetration graph (EPG) revealed that cycloxaprid significantly increased the total time of non-probing periods and greatly inhibited phloem ingestion of treated aphids because it significantly reduced the total time and the frequency of phloem ingestion. Furthermore, cycloxaprid can increase the phloem salivation of treated aphids by comparison with aphids treated with imdacloprid and distilled water. Consequently, a sublethal dose of cycloxaprid impaired aphid ingestion of phloem sap and thereby reduced the weight of aphids. On the other hand, EPG data showed that a sublethal dose of cycloxaprid had no significant effect on xylem sap ingestion, in contrast to imidacloprid. CONCLUSION All these tests indicated that cycloxaprid had both contact and root-systemic activity, with sublethal effects resulting in reduction in Sitobion avenae phloem-feeding behaviour and growth rate.

Microencapsulation of seed-coating tebuconazole and its effects on physiology and biochemistry of maize seedlings

Tebuconazole is a triazole systemic fungicide that is commonly used to treat fungal pathogens of crops, but at high doses can reduce seed germination. Seeds with microcapsulated tebuconazole were investigated to determine effects of this method on maize seedlings and the bioefficacy against maize head smut (Sphacelotheca reiliana). The ethyl cellulose (EC)-based microcapsules had encapsulation efficiency of 90.6%, and average size of 1.6 μm. A release kinetic study revealed that tebuconazole release from EC-based microcapsules fits the model (Mt/Mz=kt(n)+C). Glasshouse studies indicated that maize seedling emergence and growth were negatively affected in an exponential manner as predicted by model Y=A+B×e((-x/k)). However, microencapsulation could induce tebuconazoles growth promoting effects by increasing emergence, shoot fresh weight, root fresh weight, carotenoid and chlorophyll content. Phytohormone analysis indicated the beneficial effects of microencapsulated tebuconazole were due to the sustained release of tebuconazole that appeared to influence the balance of phytohormones in maize seedlings. Contrary to conventional tebuconazole, microencapsulated seed-coated tebuconazole can lead to slightly increased gibberellins (GA) level and disappearance of abscisic acid (ABA) accumulation in maize. In addition, microcapsule formulation of tebuconazole was found to provide better protection against maize head smut when compared to conventional formulation.

Study of inhibitory effects and action mechanism of the novel fungicide pyrimorph against Phytophthora capsici.

The antifungal activity of the novel fungicide pyrimorph, (E)-3-[(2-chloropyridine-4-y1)-3-(4-tert-butylpheny1)acryloyl]morpholin, against Phytophthora capsici was investigated in vitro. Pyrimorph inhibited different stages in the life cycle of P. capsici including mycelial growth, sporangium production, zoospore release, and cystospore germination with EC(50) values of 1.84, 0.17, 4.92, and 0.09 microg mL(-1), respectively. The effect of pyrimorph on mycelial growth was reduced by the addition of different concentrations of ATP, which suggested that the action mechanism of pyrimorph was connected with impairment of the energy generation system. Meanwhile, pyrimorph exhibited certain inhibition on metabolic approaches of Embden-Meyerhof-Parnas (EMP), tricarboxylic acid cycle (TCA), and hexosemonophosphate (HMP) by measuring the oxygen consumption of pyrimorph combining with three representative inhibitors to the metabolic approaches. The results indicated that pyrimorph could inhibit the approach of HMP significantly. Morphological and ultrastructural studies showed that pyrimorph caused excessive septation and swelling of hyphae, distortion and disruption of most vacuoles, thickening and development a multilayer cell wall, and accumulation of dense bodies. These results suggested pyrimorph exhibited multiple modes of action including impairment of the energy generation system and effect on cell wall biosynthesis directly or indirectly.

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.

Molecular Cloning, Characterization and Expression Profiling of a Ryanodine Receptor Gene in Asian Corn Borer, Ostrinia furnacalis (Guenée)

Ryanodine receptor (RyR) Ca2+ 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.

Development of melamine–formaldehyde resin microcapsules with low formaldehyde emission suited for seed treatment

To reduce the application frequency and improve the efficacy of insecticides, melamine-formaldehyde (MF) resin microcapsules suited for seed treatment containing a mixture of fipronil and chlorpyrifos were prepared by in situ polymerization. A formaldehyde/melamine molar ratio of 4:1 yielded microcapsules with the smallest size and the most narrow size distribution. The level of unreacted formaldehyde in the microcapsule suspension increased proportionally with the F/M molar ratio. When the MF resin microcapsule suspension was used as a seed treatment to coat peanut seeds, the unreacted formaldehyde did not significantly inhibit the seedling emergence, but the ongoing release of formaldehyde generated from the degradation of MF resins played an important role in inhibiting emergence. Melamine was shown to be an effective formaldehyde scavenger that mitigated this inhibition when it was incorporated within the microcapsule wall. Field experiments showed that MF-resin-encapsulated mixtures of fipronil and chlorpyrifos have much greater efficacies against white grubs than the conventional formulation.

Design, synthesis and fungicidal activity of 11‐alkoxyimino‐5,6‐dihydro‐dibenzo[b,e] azepine‐6‐one derivatives

BACKGROUND Macrocyclic compounds with an oxime ether side chain, discovered in Wangs group, showed good fungicidal activity. However, the long synthetic route makes the cost too high for them to be developed further as practical fungicides. Alternative compounds with good fungicidal activity and an easier synthesis than the above-mentioned macrolactams were sought, and a series of 11-alkoxyimino-5,6-dihydro-dibenzo[b,e]azepine-6-one derivatives (4) were designed and bioassayed. RESULTS The structures were confirmed by (1) H NMR, (13) C NMR and LC-MS. The bioassay showed that about half of the 11-alkoxyimino-5,6-dihydro-dibenzo[b,e]azepine-6-one derivatives (4) displayed good fungicidal activity against Sclerotinia sclerotiorum (Lib.) de Bary, with EC50 values <15 µg mL(-1) . 11-(n-Butyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-05), 11-(4-nitrobenzyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-12) and 11-(2-chloro-6-fluorobenzyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-21) displayed excellent fungicidal activity, with EC50 values of <2.5 µg mL(-1) , much better than the commercial fungicide chlorothalonil with an EC50 value of 7.16 µg mL(-1) . In addition, about half of the 11-alkoxyimino-5,6-dihydro-dibenzo[b,e]azepine-6-one derivatives (4) had good fungicidal activity against Botrytis cinerea (De Bary) Whetzel, with EC50 values of <10 µg mL(-1) . 11-(2-Fluorobenzyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-16), 11-(3-fluorobenzyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-17) and 11-(2-chloro-6-fluorobenzyloxyimino)-5,6-dihydro-dibenzo[b,e]azepine-6-one (4A-21) displayed excellent fungicidal activity, with EC50 values of 3.73, 2.54 and 3.20 µg mL(-1) respectively, comparable with the commercial fungicide procymidon with an EC50 value of 2.45 µg mL(-1) . Their structure-activity relationship is discussed. CONCLUSIONS The present work demonstrates that the title compounds show promise as fungicides.

Primary study on mode of action for macrocyclic fungicide candidates (7B3, D1) against Rhizoctonia solani Kuhn.

A novel macrolactam fungicide candidate (7B3) and a novel aza-macrolactone fungicide candidate (D1) were designed and synthesized, and the bioassay showed that both displayed excellent fungicidal activity against Rhizoctonia solani Kuhn. To elucidate the biochemical mode of action of the two compounds against R. solani and illustrate the similarities and differences of action mechanism resulting from subtle differences in structure of the two compounds, the effects of the two compounds on the ultrastructure of hyphae, electrolyte leakage, and respiration of mycelia cell suspension caused by 7B3 or D1 were studied. The results showed that the two compounds had very similar modes of action. Both induced irregular swelling of hyphae, vacuolation of cytoplasm, and thickening of cell wall. The conductivity of mycelia cell suspension increased in the presence of 7B3 or D1, which indicated that the two compounds had a similar effect on cell membrane permeability. In addition, both 7B3 and D1 were insufficient in inhibiting the respiration of mycelia.

Controlled Release Study on Microencapsulated Mixture of Fipronil and Chlorpyrifos for the Management of White Grubs (Holotrichia parallela) in Peanuts (Arachis hypogaea L.)

This study was conducted to determine the release dynamics of a microencapsulated mixture of fipronil and chlorpyrifos in peanut fields and its efficacy against white grubs. The results indicated that microencapsulation significantly stabilized this mixture against degradation in the environment so that a single dose of this microencapsulated formulation applied through seed treatment effectively controlled white grubs throughout the entire growing season. During the experimental course, the concentration of chlorpyrifos in the soil with the microencapsulated formulation was 13.6 ± 9.9 (n = 6) times that of the conventional formulation, and the concentration of fipronil was at least 2.2 times that of the conventional formulation in the soil and peanut roots. However, the residue risks of chlorpyrifos and fipronil in the kernels were different. At harvest, there was a low risk that the residual chlorpyrifos in the kernels exceeded the MRLs (maximum residue limit). In contrast, the amount of residual fipronil in some kernel samples reached the statutory MRL set by the European Union, which suggested that a higher application rate or the repeated application of the microencapsulated fipronil formulation would not be acceptable.

Effects of Droplet Distribution on Insecticide Toxicity to Asian Corn Borers (＂Ostrinia furnaealis＂) and Spiders (＂Xysticus ephippiatus＂)

Distribution of horizontal boom produced droplets downwards into maize canopies at flowering period and its effects on the efficacies of emamectin benzoate, lambda-cyhalothrin and chlorantraniliprole against the second generation of Asian corn borer (ACB) larvae and their toxicity to spiders were studied. When insecticides were sprayed downwards into the maize canopies, randomly filtering out droplets by upper leaves led to great variations of droplet coverage and density within the canopies. Consequently, the efficacies of lambda-cyhalothrin and emamectin benzoate against ACB larvae were decreased because of randomly filtering out droplets by upper leaves. But field investigation showed that lambda-cyhalothrin was extremely toxic to hunting spiders, Xysticus ephippiatus, and not suitable to IPM programs in regulation of the second generation of ACB. Therefore, randomly filtering out droplets by upper leaves decreased lambda-cyhalothrins efficacy against ACB larvae, but did little to decrease its toxicity to X. ephippiatus. Amamectin benzoate can reduce the populations of X. ephippiatus by 58.1-61.4%, but the populations can recover at the end of the experiment. Chlorantraniliprole was relatively safe to X. ephippiatus. It only reduced the populations of X. ephippiatus by 22.3-33.0%, and the populations can totally recover 9 d after application.