Abstract:
Agriculture is the backbone of many developing countries. However, it is facing many
challenges like changing climate, urbanization, environmental degradation, the existence
of insect pests and diseases. Among insect pests fall armyworm is one of the challenges in
the sector. It is a major insect pest of maize and other crops and causes of annual losses
of 57%, 20-50% and 30% loss of crop in Brazil, Africa and Ethiopia respectively.
Currently, farmers use chemical insecticides to reduce such losses. However, chemical
insecticides cause the development of insecticidal resistance in insects, environmental
pollution, human health hazards, harm to non-target species, etc. Therefore, as a result
of the pitfalls of chemical methods agrarian look for safe and effective alternative
approaches, biological control to fall armyworm. Bacillus thuringiensis (Bt) based
biopesticide is a major alternative to solve these problems. Bt is a gram-positive, sporeforming bacterium and it produces insecticidal crystal (Cry) proteins during sporulation.
The crystal proteins can create pores in epithelial cells of midgut of insect. This can
result free flow of ion and water into the cells. Finally, cells swell; lysis and then insects
can die. This study aimed to isolate and characterize local Bt isolates from soil and water
sample of different sites in Amhara (Abdrafi, Metema, Rasdashin, Maraki) and (Dubeti)
Afar Region and laboratory testing of their insecticidal activity against fall armyworm.
The study was conducted at the University of Gondar at Cellular and Microbial
laboratory.The data was analyzed using Analysis of Variance. A total of 18 soil and
water samples were collected from all study sites to isolate Bt variety. Morphological and
biochemical methods were used to characterize and identify Bt isolates. The antibiotic
screening was also conducted for the 7 potential Bt isolates. Each isolate was screened
for insecticidal activity against fall armyworm. Based on results, a total of 21 Bt isolates
were recovered from 102 bacillus species- Bt like a colony and the overall Bt index
corresponding to the whole sampling areas was 0.2. All isolated Bt were positive for
catalase and indole test, but the isolates showed variation for the other tests. From total
isolates, 7 isolates had a high potential to kill FAW within 72 hrs and they were (100%)
exhibited active motility, hemolytic activity, starch hydrolysis activity, indole, catalase
and MSA positive. Those potential isolates were resistant to ampicillin and cotrimoxazole
but they were sensitive to erythromycin and bacitracin except W3C and Abo2WRF. W3C
and M8E isolate were best as compared to other potential isolates, including reference
strains because they were killed after 48 hrs. To conclude Screening of soil and water
samples from different sources and habitats may be useful to obtain potential Bt isolates
with broader host ranges and high potential for insecticidal activity. As recommendation,
since this study did not address the molecular characterization, the types of Cry genes of
the isolates were not identified. Therefore, molecular characterization is recommended
