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
2015
Nian, Xiao‐ge | He, Yu‐rong | Lu, Li‐hua | Zhao, Rui
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⁻¹or B. thuringiensis 222.5–890 µg mL⁻¹with the fungus significantly enhanced fungal efficacy. The LC₅₀values of the fungus declined over a 1–7 day period after exposure, and the LT₅₀values decreased with increasing concentration. Based on LC₅₀or LC₉₀estimates, synergism between the fungus and beta‐cypermethrin resulted in a 2.7–28.3‐fold reduction in LC₅₀values and a 12.1–19.6‐fold reduction in LC₉₀values, while synergism of the fungus with B. thuringiensis led to a 2.4–385.0‐fold reduction in LC₅₀values and a 4.4–151.7‐fold reduction in LC₉₀values. CONCLUSION: 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
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