Combined use of entomopathogenic fungi and their extracts for the control of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae)

•Isolates of Beauveria and Metarhizium genera were pathogenic against S. littoralis larvae.•The most of their crude extracts were toxic for S. littoralis larvae.•Spray application of crude extracts did not cause mortality on S. littoralis larvae.•Combined application of EF and their extracts obtained additive effect at high doses.

Both the virulence and insecticidal activities of the crude extracts of 26 isolates of the entomopathogenic mitosporic ascomycetes Metarhizium sp. and Beauveria sp. (Ascomycota, Hypocreales) were evaluated against the second-instar larvae of Spodoptera littoralis (Boisduval) (Lepidoptera, Noctuidae), a very harmful polyphagous insect pest. Although all isolates caused infection when the second-instar S. littoralis larvae were immersed in the conidial suspensions, only four isolates of Beauveria (EABb 01/33-Su, EABb 01/88-Su, EABb 01/103-Su, and 3155) and one isolate of Metarhizium caused >50% mortality of the larvae, with average survival times (ASTs) of 9.67 and 8.73 days for the isolates EABb 01/33-Su and EABb 01/88-Su, which caused the highest mortality rates of 78.33% and 75.00%, respectively. The LC50 and LT50 values were 5.69 × 106 conidia ml−1 and 6.76 days for EABb 01/33-Su and 1.05 × 107 conidia ml−1 and 7.02 days for EABb 01/88-Su. By contrast, the crude extracts obtained from the Metarhizium brunneum EAMb 09/01-Su and EAMa 01/58-Su isolates caused the highest mortality rates of 80.00% and 66.66% and the lowest ASTs of 5.13 and 4.43 days, respectively. Topical application of the crude extracts did not cause mortality. Combined treatments with fungal suspensions of the isolates EAMb 09/01-Su and EAMa 01/58-Su and their extracts caused higher mortality rates than the single isolates and extracts, with the increases occurring in a dose-dependent manner, and with mortality rates reaching 100% for the EAMb 09/01-Su isolate and its extract at 1 mg ml−1 and 76% for the EAMa 01/58-Su isolate and its extract at 1 mg ml−1. The combination of the maximal concentrations of both fungi and crude extract had an additive effect on larvae, resulting in 100% mortality for the combination of the extract EAMb 09/01-Su with the strains EABb 01/33-Su and EAMb 09/01-Su. These results show the potential of certain entomopathogenic fungal isolates for use in an integrated S. littoralis management strategy targeting larvae, as well as the potential of the combined use of entomopathogenic fungi and their extracts.

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