title: Evaluation of the time-concentration-mortality responses of Plutella xylostella larvae to the interaction of Isaria fumosorosea with the insecticides beta-cypermethrin and Bacillus thuringiensis.
abstract: BACKGROUND
  Entomopathogenic fungi are potential candidates for controlling Plutella xylostella, a cosmopolitan pest of crucifers. In this study, bioassays were conducted to evaluate the interaction between Isaria fumosorosea and sublethal doses of two insecticides, beta-cypermethrin and Bacillus thuringiensis, against P. xylostella.
  
  
  RESULTS
  Data of each assay were in good agreement with the time-concentration-mortality model, indicating a strong dependence of the fungus and insecticide interaction on both concentration and post-exposure time. Using beta-cypermethrin 58-116 µg mL(-1) or B. thuringiensis 222.5-890 µg mL(-1) with the fungus significantly enhanced fungal efficacy. The LC50 values of the fungus declined over a 1-7 day period after exposure, and the LT50 values decreased with increasing concentration. Based on LC50 or LC90 estimates, synergism between the fungus and beta-cypermethrin resulted in a 2.7-28.3-fold reduction in LC50 values and a 12.1-19.6-fold reduction in LC90 values, while synergism of the fungus with B. thuringiensis led to a 2.4-385.0-fold reduction in LC50 values and a 4.4-151.7-fold reduction in LC90 values.
  
  
  CONCLUSIONS
  Results show that sublethal doses of B. thuringiensis and beta-cypermethrin can synergise I. fumosorosea activity on P. xylostella, suggesting that combination of I. fumosorosea with the two insecticides might offer an integrated approach to controlling P. xylostella in practice. © 2014 Society of Chemical Industry.
authors.affiliation: College of Resources and Environment, South China Agricultural University, Guangdong, Guangzhou, China.
authors.forename: Xiao-ge
authors.initials: XG
authors.lastname: Nian
authors.forename: Yu-rong
authors.initials: YR
authors.lastname: He
authors.forename: Li-hua
authors.initials: LH
authors.lastname: Lu
authors.forename: Rui
authors.initials: R
authors.lastname: Zhao
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis; D004305:Dose-Response Relationship, Drug; D006999:Hypocreales / Q000502:physiology*; D007300:Insect Control; D007306:Insecticides; D007814:Larva / Q000382:microbiology; D009036:Moths / Q000254:growth & development / Q000382:microbiology; D010143:Paecilomyces / Q000502:physiology; D010572:Pest Control, Biological; D011722:Pyrethrins; D013997:Time Factors
chemical_list: D007306:Insecticides; D011722:Pyrethrins; C017160:cypermethrin
keywords: Bacillus thuringiensis; Isaria fumosorosea; Plutella xylostella; beta-cypermethrin; synergistic interaction; time-concentration-mortality modelling