Isolation, characterization, and bio-insecticidal efficiency of Ethiopian isolates of Bacillus thuringiensis against Galleria mellonella L. (Lepidoptera: Pyralidae) and tomato whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae)

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Abstract Background Bacillus thuringiensisis a Gram-positive, rod-shaped, and spore-forming microbial entomopathogen. The silverleaf whitefly,Bemisia tabaci(Genn.) (Hemiptera: Aleyrodidae), is a worldwide important cryptic species causing serious economic damage to several vegetable crops including tomato. The aim of this study was to characterize and evaluate the bio-insecticidal effects of locally isolated Bacillus thuringiensis(Bt) againstGalleria mellonellaandBemisia tabaci. Results Thirty-one isolates ofBtwere obtained from 70 soil samples based on cultural characterization coupled with insecticidal crystal protein detection. All of the 31 bacterial isolates were pre-screened for their bio-insecticidal property against the greater wax moth,Galleria mellonellaL. larvae. Only 20 (64.5%) isolates were virulent toG. mellonellawith a percentage mortality that ranged from 2.50 to 95%. The groEL gene sequences of all 20 entomopathogenic indigenous isolates displayed 99–100% similarity withBtisolates. Bioassay evaluation of 12 selected isolates against 3rd to 4th nymphal instars ofB. tabaciwith spore-crystal suspensions of 1 × 109spores/ml caused 0 to 31.25%, 0 to 57%, and 0 to 82.5% percentage mortality within 48, 96, and 144 h accordingly. Among isolates ofBt, isolate AAUDS-16 had the highest virulence, followed by the isolate AAUES-69D with LC50values of 9.67 × 106spores/ml and 1.16 × 107 spores/ml, respectively. The virulent isolates were tested for their growth response to a different temperature range between 15 and 40 °C. All isolates showed a maximum growth rate around 30 °C. Conclusions Btisolates of AAUES-69D and AAUDS-16 displayed high insecticidal potential againstB. tabacinymphs andG. mellonellalarvae, and showed a maximum growth rate in a wide range of temperature. High virulence and temperature-tolerant isolates should be important candidates for diverse insecticidal toxin studies.

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