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 isolated Metarhizium anisopliae (Metsch.) (Sorokin), against larvae of T. absoluta. Twenty-five Metarhizium isolates were isolated from different soil types, using the great wax moth, Galleria mellonella L. baiting method. From these, 13 isolates were prescreened by biological efficiency index model and tested against 2nd and 3rd larval instars of T. absoluta at the concentration of 10(7) spores ml(-1). Sterile water plus Tween 80 (0.1% v/v) was used as a control. Greenhouse reared larvae of T. absoluta were used as experimental organisms. All tested Metarhizium formulations were pathogenic to T. absoluta in 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 of T. 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 with F (24, 50) = 6.825, p < 0.001 and F (23, 15) = 3.97, p < 0.001 of mortality to 2nd and 3rd larval instars, respectively. Molecular analysis categorized these selected isolates under species of M. anisopliae and grouped into 2 different groups. AAUM78 and AAUM39 were recorded LT50 values of 3.93 and 3.5 days at the lowest (10(4) spore ml(-1)) concentration and LC50 values of 1.2 x 10(3) and 2.9 x 10(3) spore ml(-1), respectively. Although AAUM78 and AAUM39 were virulent to the target pest, further field evaluation is required to determine their potential efficacy for T. absoluta control.