KRITCHAYA ISSAKUL1, ELKE PAWELZIK1, ARAYA JATISATIENR2, CHAIWAT JATISATIENR2, SUCHADA VEARASILP3
1Georg-August-Universität Göttingen, Department of Crop Science, Germany
2Chiang Mai University, Department of Biology, Thailand
3Chiang Mai University, Department of Agronomy, Thailand
The application of botanical insecticides is one of alternative ways to reduce the use of harmful insecticides in agricultural pest management. Nine species of Thai local plant extracts with known insecticidal properties i.e. Acorus calamus, Eugenia caryophyllus, Mammea siamensis and 6 species of Stemona (S. curtisii, S. tuberosa, S. burkillii, S. kerrii, Stemona unknown 1 and Stemona unknown 2) were screened for the highest insecticidal activity by the Brine Shrimp Lethality Test (BST). M. siamensis expressed a very strong toxic effect on brine shrimp with the lowest 24 hour LC50 value of 0.072mgL-1. The purification of its active compound was conducted using chromatographic methods and the BST to select the most effective fraction. The spectroscopic method i.e. MS, IR and NMR were used for the identification of the active compound. Surangin B was finally identified as the active compound. Its insecticidal effectiveness on the 3rd instar larvae of diamondback moth was investigated by topical application and leaf dipping methods in comparison with methomyl. The results indicated that surangin B demonstrated a higher contact activity than methomyl with 24 hour LC50 values of 0.07 and 0.51gL-1, respectively. Moreover, surangin B also had a stronger antifeedant activity than methomyl with the percent of leaf area damaged of 0.83 and 0.14% for the surangin B concentration of 0.5 and 1.0gL-1, respectively. However, methomyl exhibited a lower toxicity with 3.19 and 1.65% leaf area damaged for the methomyl concentration of 0.5 and 1.0gL-1, respectively. From the results it can be concluded, that mammea extract might be one of the natural insecticides for the diamondback moth management. However, before the future promotion, its efficiency under field conditions, effects on agricultural products and the ecosystem should be tested for confirmation of its insecticidal effectiveness and safety.
Keywords: Botanical insecticide, diamondback moth, plant extract, surangin B