Author : Soontorn Pipithsangchan

Summary : The unilateral approach in trying to overcome the DBM problems with synthetic insecticides by the farmers has itself generated other undesirable effects, which elicited interest on the possible use of botanical insecticide against DBM. Ethanol extracts and volatile oils from specific parts of five different plant species, (Zingiber zerumbet, rhizome; Costus speciosus, rhizome; hymenodictyon excelsum, bark; Gynandropsis gynandra, whole plant and Mentha cardiafolia, whole plant), were evaluated for their insecticidal activities on the third instar larvae of diamondback moth (DBM), Plutella xylostella (L.). The high contact toxicity by topical application was observed on both ethanol extract and volatile oil from C. speciosus (LD50=15.62 and 13.80 ug/mg body weight, respectively). The toxic properties of the ethanol extract from G. gynandra (LC50=70.82 mg/ml) as well as the volatile oil of C. speciosus (LC50=62.80 mg/ml) were also shown by leaf residue film method (LRFM). Antifeedant activity was shown by the volatile oil from Z. zerumbet, but the reduction in feeding was less than 50% compared to the control.