Biocontrol of Diamondback Moth Larvae Tolerant to Bt-toxin Dipel® by the Entomopathogenic Fungus Metarhizium anisopliae (Metschn.) Sorokin (Hypocreales, Ascomycota)
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Diamondback moth Plutella xtlostella (Plutellidae, Lepidoptera) is a destructive insect on plants of family Cruciferae. Bacillus thuringiensis toxins, abbreviated Bt-toxins, are biopesticides that could be used for control of larvae of lepidopterous insects. The efficacy of these biopesticides usually decreases due to the development of tolerance to these pesticides by the treated insects. However, this decrease could be compensated by applying biocontrol agents such as entomopathogenic fungi. The objective of the present research was to test the efficacy of Metarhizium anisopliae, as an entomopathogenic fungus, against susceptible and tolerant populations of P. xylostella larvae to Bt-toxin Dipel®. For this purpose, a series of fungus concentrations were used against susceptible and tolerant populations of P. xylostella larvae to Dipel®. Results indicated that there were significant differences (at P=0.05) between the concentrations of M. anisopliae that were used for the treatment of Bt-tolerant and susceptible larvae of P. xylostella. The biocontrol efficacy of M. anisopliae was higher in the susceptible larvae than that in the Bt-tolerant larvae at the concentrations that exceeded 1x10^6 conidia/ml. Probit analysis indicated that the LC50 of the fungus concentrations used for the treatment was 7.70x10^6 conidia/ml for the Bt-tolerant larvae vs. 1.34x10^5 conidia/ml for the susceptible larvae. In conclusion, in spite of the development of low value cross-tolerance in Bt-tolerant P. xylostella larvae to M. anisopliae treatment, there is a good possibility for including this fungus in the integrated control of the insect when develops tolerance to Bt-toxin Dipel® because of high biocontrol efficacy of the fungus.

Keywords: Biocontrol efficacy; Metarhizium anisopliae; Plutella xylostella; Bt-toxin Dipel®; Susceptible population; Tolerant population

      Abbreviations: EPF: Entomopathogenic Fungi; SDA: Sabouraud Dextrose Agar; RR: Resistance Ratio


Yacoub Batta
An-Najah National University
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