Essential Oils from Six Herbal Plants for Biocontrol of the Maize Weevil

Abstract

Essential oils from sweet basil ( Ocimum basilicum L.), holy basil ( O. americanum L.), hairy basil ( O. tenuiflorum L.), lime ( Citrus aurantifolia Swingle), kaffir lime ( C. hystrix DC.), and clove ( Eugenia caryophyllus L.) were isolated by simultaneous distillation extraction. Toxicity assays against the maize weevil ( Sitophilus zeamais Motschulsky) using 30 to 120 μL oil extract from the six plants on 70-mm-diameter filter paper discs resulted in 100% weevil mortality within the 5-h assay period. On rice samples, sweet basil oil extract was the most effective, resulting in 96% to 100% mortality regardless of oil extract volume on the first day during the 5-day assay period. Probit analysis showed that sweet basil oil extract applied on grains had four to five times lower LD 50 (lethal dose to kill 50% of the weevils) and two to three times lower LD 99 values than the remaining oil extracts. Repellency assay using 1 to 8 μL oil extract showed a different trend, because hairy basil was the most effective among treatments. Based on the effective control of the maize weevil by the oil extracted from herbal plants, such oil extracts could be useful in stored agricultural products and plant protection and reduce the risk associated with synthetic insecticides.