Management of Cabbage Aphid (Brevicoryne brassicae L. (Homoptera: Aphididae)) on Ethiopian Mustard (Brassica carinata Braun) using Entomopathogenic Fungi and Selected Insecticides

Abstract

Cabbage aphid (Brevicoryne brassicae L.) is an important sucking insect pest of cabbage and other vegetables. It can be controlled using continuous chemical insecticides that cause human health and environmental problems. The present study was, therefore, designed to evaluate antagonistic activities of indigenous entomopathogenic fungi together with selective insecticides within the context of integrated pest management (ipm). To this effect, four strains of entomopathogenic fungi from Beauveria bassiana and Metarhizium anisopliae were tested for their antagonistic activities against the cabbage aphid. The result showed that microbial inoculums of 1×10⁷ and 1×10⁸ conidia mL^-1 showed high mortality (66.7-100%) of aphids after 6 days of incubation under laboratory condition. Among them, bei1 (B. bassiana) isolate was the most virulent strain on adult aphids and nymphs showing 67 to 100% and 39-72% mortality after 4^th-5^th days of treatments. The data also indicated that the fungal isolates were compatible to the three insecticides with 70% - 91% conidial germination by M. anisopliae and 68%-98% conidial germination by B. bassiana after 24 hours of treatment of which Karate was the most compatible insecticide to the isolates. The single treatment with the entomopathogens gave a substantial percentage mortality of insect pests after 11 days compared to (80-100%) mortality obtained from a combined treatment with half recommended dose of Karate in seven days, which was similar to the treatment with full dose of the insecticide control. The treatments were slightly more effective on adults than they were on aphid larvae.  It is interesting to note that the combination of bei1 + Ka induced 100% mortality of adult aphids after seven days of incubation compared to the 11 day incubation required to kill the nymphs. Given that the full dose of karate killed the adult aphids in five days, the 100% mortality of the half dose of karate with bei1 within seven days was a good indication that the ipm could reduce pollution problem. Thus, B. bassiana and M. anisopliae with Karate could be further tested in the field to realize their potential as bioinsecticides for integrated pest management to control mustard aphids.