Isolation, bioassay and field evaluation of some Philippine plants for insecticidal activity; 1: shrubs [Philippines]
1988
Rejesus, B.M. | Maini, H.A. | Garcia, C.M.
A total of 19 Philippine plant species have been evaluated for their insecticidal action. Ten insects belonging to different orders used in the laboratory/greenhouse evaluation of the plants are given. The ethanolic extracts of nine plants were toxic to some of the test insects and the mortality varied from 20-50%. Ethanolic extracts giving less than 50% mortality were eliminated for further study. Due to ease of extraction and high solubility of volatile oil to the solvent used for bioassay, work on five volatile oil containing plant namely: sambong, oregano, lagundi, bulak-manok and manzanilla were pursued. They were toxic to several test insects belonging to four orders (Lepidoptera, Homoptera, Hemiptera, and Diptera) while their activity varied with the coleopterous test insects. Based on LD50 values, sambong was toxic to stored grain pests, corn weevil (CW), lesser grain borer (LGB), and red flour beetle (RFB) at 1.06, 2.18 and 2.6 mg/g body weight, respectively. Oregano and bulak-manok were most toxic to CW at 0.34 and 0.62 mg/g body weight, respectively, both were toxic less than malathion. The most toxic against LGB was bulak-manok at 1.04 mg/g body weight. All four volatile oils except manzanilla were more toxic than malathion to diamondback moth (DBM). Lagundi and oregano were more toxic to common cutworm (CC) and all volatile oils except sambong were toxic to armyworm (AW). Sambong is acting as a repellant while oregano has a knockdown effect against Azuki bean weevil (ABW). This paper also discussed isolation of the possible active fraction and bioassay for toxic, antifeedant/repellant actions; bioassay for other insecticidal mode of action (insect growth regulator, sterilant, etc.); laboratory studies on methods of preparing plant materials for pest control and field test simple methods of using the plant material.
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