The food consumption pattern of Colorado potato beetle larvae revealed that the food intake increased exponentially with larval age, with the penultimate and ultimate instars larvae consuming18 and 73% of the total, respectively. Different larval stages of Colorado potato beetlewere treated by different doses of Bcillus thuringiensis Berliner var. tenebrionis under laboratory conditions to determine larval susceptibility to this bioinsecticide. The results indicated that in terms of LD₅₀ values younger larvae were more susceptible to the B. thuringiensis than older instars. LD₅₀ values estimated from the collected data indicated a different pattern of susceptibility of larvae to B.t. for different larval stages, as evidenced by non overlapping confidence intervals of relative median potency estimates The LT₅₀ values showed that the speed of larval death depends on the larval age and B. thuringiensis dose. It was concluded that, if the pattern of food consumption and susceptibility in the present study was used as a model of larval food intake and susceptibility under natural conditions, the larvae must be killed prior to penultimate instar.