Integrated Pest Management of Cabbage Aphid (Brevicoryne brassicae L.: Aphididae) on Ethiopian Mustard (Brassica carinata A. Braun) using Entomopathogenic Fungi and Selected Insecticides
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Date
2017-02
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Addis Ababa Universty
Abstract
Insect pests are responsible for most of the yield loss of horticultural plants, of which cabbage aphid (Brevicoryne brassicae (L.) is emerging as important sucking insect pest of cabbage crops. The indiscriminate use of insecticides against insect pests is becoming hazardous to environmental and human health, and ineffective because of the development of resistance against the chemicals. This necessitates the search for integrated pest management using living micro-organisms alone or with little or no application of chemicals to reduce chemicals and produce quality food. The present study was, therefore, designed with the objective of isolating and characterizing antagonistic local isolates of entomopathogenic fungi against aphid. Accordingly, isolates Beauveria (BEI1, BEI2) and Metarhizium (MEI1,MEI2) were collected from several forest soil samples and screened for their compatibility with different insecticides. The dose and time dependent antagonistic tests in vitro and in vivo against the aphid was observed. Accordingly, microbial inoculums of 1×107 and 1×108 conidia mL-1 showed high mortality (66.7-100%) of aphids after 6 days under laboratory conditions. Among the isolates, BEI1 isolate was the most virulent against adult and nymphs aphids. However, higher mortality was recorded on adult aphids (67-100%) as compared to nymphs (39-72%) after 4th-5th day of treatment. The in vitro compatibility test of the isolates with 3 chemical pesticides; Karate(50 ml ha–1), Actara (20g ha–1) and Radiant( 100 ml ha–1) at formulations of (Field rate, 0.75Field rate and 0.5Field rate) concentrations showed 70% -91% conidial germination rate by M. anisopliae, MEI1, MEI2 and 68%-98% conidial germination rate by B. bassiana (BEI1, BEI2). Although not significantly different, the insecticide Karate was more suppressive for spore germination followed by Actara and Radiant suggesting the possibility of using these insecticides together with the entomopathogens for integrated pest management. Similarly, the in vivo experiment also showed variations (P= 0.001) among the different treatments. Consequently, the treatment of cabbage aphid with 0.5Field rate karate with all entomopathogenic fungi showed mortality ranging from 21% -100% and 28.3% - 100% after 3-11 days compared with 45.6% -100% and 52.8-100% mortality rate of nymph and adult aphids respectively with treatments using field rate karate. The data also showed that effectiveness in the in vivo study took more days (11) than those in vitro studies (6)days. The combined application of insecticide sequentially with selective fungi proved to be synergistic given more control than the fungal isolates alone. Keywords: Bio-pesticides, Entomopathogenic fungi, Compatibility, Germination, Mortality
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Bio-pesticides, Entomopathogenic fungi, Compatibility, Germination, Mortality