The study of biological differences between two native isolates of Bacillus thuringinesis (KH4 and GN9) on potato leaf beetle Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)

Colorado potato beetle Leptinotarsa decemlineata Say has numerous hosts as a serious potato pest. There are several biological control agents which are used to control the pest and Bacillus thuringiensis can be the most important. In order to estimate the LC50, this study started by the bioassay performed with the standard cultured isolate from the Custom BC sample. The concentration killing 50% of larva population was assessed as 2506.63 CFU/ml. Probit statistical software was used to show the difference among native and standard isolates in a complete random design. Two native isolates (KH4 and GN9) were used as treatments. The variance analysis and comparing the mean mortality percentage of Colorado potato beetle in second instar larvae demonstrated a significant difference between treatments and the standard isolate in all the concentrations. The standard isolate had the highest mortality percentage of 62% and the native isolates showed less than 5% of mortality. It is understood that the selection of the proper concentration (about LC50) and comparison of the mortality percentage in that concentration is an appropriate method for the screening the isolates and make a lot of time and money saved.