This study was designed to develop a microemulsion formulation of norcantharidin for the control of the diamondback moth (DBM), Plutella xylostella (Linnaeus), a notorious pest of brassica crops worldwide. The oil phase was screened and selected based on norcantharidin solubility while the surfactants were selected on the basis of their efficiency to form microemulsion. Optimized batches were selected using pseudo ternary phase diagrams. The microemulsion system were stabilized using mixtures composed of norcantharidin, surfactants (Tx13 and Tw80), and cosurfactant (ethanol). Its physicochemical characteristics were also demonstrated to have a higher cloud point than 72 °C as well as good thermodynamic and dilution stability. In additon, a subsequent insecticidal bioassay indicated that the acute LC50 for norcantharidin microemulsion to P. xylostella was estimated to be 12.477 mg/L (11.58–13.41, 95% CL). Our results provide an environment-friendly promising alternative to control P. xylostella and possibly contribute to ameliorating any pesticide resistance in P. xylostella.
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a destructive insect pest of cruciferous plants that has developed resistance to almost every listed commercial insecticide. Cantharidin as an animal-derived biopesticide is a natural defensive compound produced by Meloidae insects with toxicity to many insects including P. xylostella. Norcantharidin is an important substitute of cantharidin and has similar insecticidal activities to cantharidin. Although the toxicity of cantharidin and norcantharidin to P. xylostella has been reported, little research has focused on the effects of cantharidin or norcantharidin on the behavior of P. xylostella. In this study, we investigated the feeding behavior of third-instar larvae and the oviposition preference of adult P. xylostella in order to explore the effects of different concentrations of cantharidin and norcantharidin. Results show that cantharidin and norcantharidin have antifeedant effect on P. xylostella larvae. The values for AFC50 were 13.0228 and 149.4210 mg/ml, respectively. Furthermore, the oviposition deterrence rate of cantharidin on P. xylostella ranged from 49.37 to 58.24% and that of norcantharidin was from 20.88 to 33.33%. These results suggest cantharidin and norcantharidin may have repellent and antifeedant effect on P. xylostella, which could contribute toward using biopesticides to manage P. xylostella and may provide a new strategy for integrated pest management.
Background Endophytic bacteria have been demonstrated to be one of the most potentially important biocontrol agents for their efficiently improved plant growth and protection of host plants from infection by phytopathogens. Results Nine strains of endophytic bacteria isolated from Glycyrrhiza uralensis Fisch. (G. uralensis) seeds were screened for the inhibitory effect against 5 fungal phytopathogens by using dual culture method. Among which, the isolate FT2 showed the highest percentage of inhibition to all the test fungal phytopathogens. Detached root assay showed that FT2 significantly reduced disease index and rotted area on Angelica sinensis root slices caused by Fusarium acuminatum. FT2 also exhibited multiple plant growth promotion traits by qualitative analytical method. Based on phenotypic, physiological and biochemical characterization and genotypic characterization, the FT2 strain was identified as Stenotrophomonas rhizophila. Application of strain FT2 reduced the disease index of Cucumber Fusarium Wilt, and the biocontrol effect was equal to chemical fungicide, carbendazim. Moreover, strain FT2 increased the plant height, stem diameter, leaf number and fresh weight of cucumber seedlings and the activities of the defense-related enzymes including phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase. In addition, strain FT2 could promote seed germination and seedling growth of G. uralensis and increase enzyme activities, available nutrient contents and bacterial count in G. uralensis rhizosphere soil. Conclusions The results demonstrated that the strain FT2 could be used to develop environmentally friendly microbial products to improve the activity against pathogenic and promote plant growth.
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