Comparative evaluation of <i>Bt</i> and non- <i>Bt</i> cotton varieties against cotton Bollworm infestation in Ethiopia

The cotton bollworm is a complex biotic problem that causes 36–60% yield loss. Controlling this pest was practiced by insecticides, but efforts have been made through genetic modification to reduce pesticide use and environmental pollution. A field experiment was conducted to evaluate the efficacy of Bt-cotton against bollworms at seven different locations in Ethiopia during the 2017 cropping season. Randomized Complete Block Design with three replications and six treatments, three Bt and three non-Bt cotton varieties were used. The laboratory bioassay was conducted on 1st to 3rd instar larvae at Werer Agricultural Research Center using detached cotton leaves, squares, and bolls as feed. The result indicates significantly higher bollworm larvae populations and damaged fruiting parts were recorded on non-Bt-cotton varieties. Bt-cotton varieties reduced bollworm infestation and boll damage by 77% and 93% respectively. Seed Cotton yield and its components were also significantly affected by varieties and their interactions with Bt-cotton varieties outperforming conventional cotton varieties by 36.5%. The bioassay result shows that the highest larvae mortality was recorded on 1st instar within 24 hours. JKCH 1947 and JKCH 1050 had the highest larva mortality, with 97.9% and 90.2% larvae mortality on detached leaves, squares, and bolls feed, respectively. Overall, Bt-cotton varieties had lower bollworm larvae infestation and damaged cotton fruiting parts resulting in higher yields. Therefore, the use of this technology is the first systematic Bt-cotton evaluation in Ethiopia and an important aspect of pest management, as it is non-polluting, cost-effective, and less expensive than using synthetic insecticides.