Morphological, molecular, and pathogenicity characteristics of the native isolates of Metarhizium anisopliae against the tomato leafminer, Tuta absoluta (Meyrick 1917) (Lepidoptera: Gelechiidae) in Ethiopia

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Abstract The South American tomato leafminer,Tuta absoluta(Meyrick 1917) (Lepidoptera: Gelechiidae), is a newly introduced and a major threat of tomato production in Ethiopia. Laboratory bioassay was conducted to evaluate locally isolatedMetarhizium anisopliae(Metsch.) (Sorokin), against larvae ofT. absoluta. Twenty-fiveMetarhiziumisolates were isolated from different soil types, using the great wax moth,Galleria mellonellaL. baiting method. From these, 13 isolates were prescreened by biological efficiency index model and tested against 2nd and 3rd larval instars ofT. absolutaat the concentration of 107spores ml−1. Sterile water plus Tween 80 (0.1% v/v) was used as a control. Greenhouse reared larvae ofT. absolutawere used as experimental organisms. All testedMetarhiziumformulations were pathogenic toT. absolutain all conducted bioassays. Three isolates, AAUM78, AAUM39, and AAUM76, were the most effective and scored 88, 90, and 95% and 90, 93.3, and 95.7% mortality against 2nd and 3rd larval instars ofT. absoluta, respectively. The lowest (48.5 and 50%) mortality rate was recorded by isolate AAUM30 against 2nd and 3rd larval instars, respectively, in 7 days post inoculation. However, all isolates showed significant statistical differences withF(24, 50) = 6.825,p< 0.001 andF(23, 15) = 3.97,p< 0.001 of mortality to 2nd and 3rd larval instars, respectively. Molecular analysis categorized these selected isolates under species ofM. anisopliaeand grouped into 2 different groups. AAUM78 and AAUM39 were recorded LT50values of 3.93 and 3.5 days at the lowest (104spore ml−1) concentration and LC50values of 1.2 × 103and 2.9 × 103spore ml−1, respectively. Although AAUM78 and AAUM39 were virulent to the target pest, further field evaluation is required to determine their potential efficacy forT. absolutacontrol.

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