Investigation of the effect of native isolates of the bacterium, Bacillus thuringiensis on mortality of Mediterranean flour moth

Today, microbial pest control, including the use of Bacillus thuringiensis (Bt), has become important because of its adaptability to the environment and the provision of healthy food. In this study, native isolates of Bt were isolated and selected from the soil of different regions with sodium acetate selective method. The isolates were initially identified with Coomassie brilliant blue staining which were divided into ۱۳ groups according to the shape of the crystal proteins. The spherical and irregular shapes were observed the most frequently. To determine the pathogenicity of the isolates, after purification of spore-crystals, a ۲۰۰۰ μg -suspension of each isolate in ۱ ml distilled water was prepared. The mentioned suspensions were mixed with one gram flour and ۱۵ larvae of Ephestia kuehniella were treated with the mixtures in three replicates. Two bacteria included Bt thuringiensis (Btt) and Bt kurstaki (Btk)were used as the positive controls. The test was done as a completely random design and the averages were compared by the Tukey’s test at the probability level of ۵%. The isolate (۱۰۵۳) collected from Chenaran- Khorasan Razavi had the highest percent mortality (۷۷.۱۴±۶.۴۴%). Btt along with the two native isolates (۱۰۸۰ and ۱۰۸۴) showed the lowest mortality (۴.۶۰±۱.۰۸, ۱۱.۲۶±۲.۰۶ and ۲۱.۲۷±۲.۸۲ %), respectively. The two other native isolates including ۱۰۹۰ and ۱۰۸۷ as well as Btk mostly had around ۵۰% mortality. However, there is no significant difference among the rest of nine isolates, which had up to ۵۰% mortality. The most pathogenic isolate (۱۰۵۳), had ovoid , spherical and irregular shape of crystals and was isolated from the soil under the pear trees. These isolates could be a source of new genes with high lethality and used in integrated pest management to control farm and stored product pests.

کلیدواژه ها:

Biological control ، Pathogenicity ، Coomassie blue ، Spore-crystal