Efficacy of plant derived and synthetic insecticides against cabbage aphid, Brevicoryne brassicae (L.) (Homoptera: Aphididae) and their effect on coccinellid predators

Cabbage aphid, Brevicoryne brassicae (L.)  is one of the major insect pests of brassica crops worldwide. Mainly insecticides are being used for its management which poses hazardous effects on the environment and the applicator. Low efficacy and non-target effect of the available insecticide are the main challenge in the management of the pest in Ethiopia. The use of bio-rational and neonicotinoid pesticides is a promising alternative as they are less vulnerable to resistance development and relatively safe to the environment and the applicator. This study was carried out in 2018/19 cropping season to evaluate the efficacy of plant derived and synthetic insecticides for the management of cabbage aphid and their effect on coccinellid predators on Ethiopian kale. Ten treatments including six synthetic and two botanical insecticides were tested in comparison with the standard check dimethoate 40% EC and the untreated control in Randomized Complete Block Design with three replications. Significant (P<0.05) differences were observed among the treatments in terms of cabbage aphid population reduction and their effect on coccinellid beetles. The botanical mix (Garlic+onion+pepper) and imidacloprid were at par with each other and found to be the best treatment with 93.79% and 91.04% efficacy, respectively. The maximum leaf yield was obtained from imidacloprid (14.18 t/ha) followed by botanical mix (13.45 t/ha) and lufenuron (12.42 t/ha). The highest yield increment over control was obtained from imidacloprid (3.1 t/ha), followed by botanical mix (2.37 t/ha). The botanical mix, imidacloprid and neem seed extract were highly effective in aphid control as well as less hazardous to ladybird beetle (Coccinella septempunctata L.). The highest cost benefit ratio was recorded with profenofos (1:1.14) followed by lufenuron (1:0.2), spinosad and nimbecidine (1:0.18). Results of the current study demonstrated that imidacloprid and plant-based insecticides can reduce aphid populations equally to conventional insecticides and could be used as an alternative component for the integrated pest management (IPM) of cabbage aphid, Brevicoryne brassicae (L.) on kale crop under field condition of smallholder farming system