Author(s): Zemedkun Alemu
Studies on the level of synthetic pyrethroid insecticides (lamdacyhalothrin, deltamethrin and alphacypermethrin) resistance in African bollworm, Helicoverpa armigera was carried out at Werer agricultural research center. The level of resistance was evaluated under the laboratory conditions on four populations using larva immersion and square dip methods. The selected insecticides were tested in seven dilutions levels. In each dilution 30 larvae of 3 rd instars H. armigera were treated in three replications along with pure water. Low level of resistance was detected for all tested locations to alphacypermehtrin and high resistance ratio to lambda-cyhalothrin and deltamethrin for Gewane and Werer populations. Aplhacypermethrin was the most toxic insecticide and its LC50 was low compared to other tested synthetic pyrethroids. Whereas, deltamethrin was the least toxic insecticide with high LC50. The LC50 value of Goffa-Sawla population was significantly different among the populations for Werer, Upper-Awash and Gewane in both bioassay methods. The study concluded that Helicoverpa armigera might have resistant to deltamethrin in Werer and Gewane populations. Further studies on monitoring of resistance are recommended.
