Frequency and distribution of <i>Bacillus Thuringiensis from Ethiopian soils

Abstract

Search for B. thuringiensis with novel crystal proteins and effectiveness against insect pests from soils and other environments is underway worldwide. In the present study, B. thuringiensis were isolated from various agro-ecological soils of different zones in Ethiopia and larvicidal activity of isolates was determined using insect bioassay. Of the 503 soil samples examined, 32% yielded B. thuringiensis. B. thuringiensis was found to be distributed in all the studied agro-ecological soils. Tepid to cool semi-arid lakes and rift valley soils yielded B. thuringiensis more frequently, followed by cold to very cold sub-humid afroalpine and hot to warm perhumid lowlands. On the other hand, B. thuringiensis was least frequent in soils from hot to warm moist lowlands and hot to warm sub-moist midhighlands. It was also shown that vegetative cover influences the distribution of the bacteria in the soil. Two hundred and thirteen B. thuringiensis isolates were tested for larvicidal activity against An. arabiensis (Diptera) and Plutella xylostella (Lepidoptera) larvae. Of the tested isolates, 44 (21%) killed 50-100% of An. arabiensis larvae within 48 hours. Isolates that killed 100% larvae within 24 hours were all from tepid to cool moist midhighland soils whereas those which killed 100% larvae within 48 hours were from three other different agro-ecological soils. None of the 110 B. thuringiensis strains tested against Plutella xylostella larvae showed any larvicidal activity.

Keywords/phrases: Agro-ecological soil, Anopheles arabiensis, Bacillus thuringiensis, Frequency of isolation, Larvicidal property, Plutella xylostella

Ethiop. J. Biol. Sci., 7(1): 55-67, 2008