Susceptibility of African Bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) to Different Commercial Pyrethroid Insecticides on Cotton

Abstract

The African bollworm, Helicoverpa armigera (Hubner) is an indigenous species in Africa and has been reported in the destruction of several crops in general and cotton in particular in Ethiopia. Currently, the management of H. armigera is mainly focused on the use of synthetic pyrethroids, which have already led to resistance selection pressure in several field populations of this insect. To know the status of different pyrethroid insecticides monitoring was exercised using populations of H. armigera collected from four different areas of the central and southern rift valley. This study aimed to screen the susceptibility pattern of four field populations of H. armigera to Aplhacypermethrin, lambda-cyhalothrin, and deltamethrin insecticides using third-instar larva immersion and square dip methods. The selected insecticides had been examined in seven concentration levels. For each concentration, thirty-third instar larvae were treated in three replications. An equal number of larvae were treated with tap water as control. The result indicated that Aplhacypermethrin displayed high acute toxicity to H. armigera populations from Werer, Gewane, and Merti Jeju whereas lambda-cyhalothrin and deltamethrin exhibited relatively low toxicity to the populations from Gewane and Werer. The LC₅₀ value of the Goffa-Sawla populace became notably exclusive to most of the populations from Werer, Merti Jeju, and Gewane in each bioassay method. The pairwise correlation coefficients of LC₅₀ values indicated that the commercial insecticides were not significantly correlated.  Therefore, it is concluded that the recorded high levels of deltamethrin resistance in H. armigera from Gewane and Werer may lead to the development of resistance to deltamethrin. Further investigation on the tracking of resistance and its management is needed.