The commercial formulation TEKNAR based on Bacillus thuringiensis serotype H-14 in the form of a liqued concentrate was applied against Larval populations in two road-side ditches near the Faculty of Science in Benha. Three experimental treating ments were carried out at a dose of 2 mg/L. Eight days following each application, treated areas had returned to pre-treatment levels of Larvae, but with differences in age distributions Laboratory bioassays were conducted to study the factors which can influence the efficiency of this Larvicide under natural conditions.