A field study was conducted to elucidate the predatory activities of the ant Oecophylla smaragdina on the bagworm Pteroma pendula in oil palm plantations at Teluk Intan, Perak, Peninsular Malaysia, from November 2010 to August 2011. The ant was found to be prevalent in taller (> 4m) palm stands but absent in shorter ones subject to a comparable regime of chemical pesticides or biological control. Among the taller palms the number of nests per tree ranged from 0 to 13. The abundance level of P.

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... endula was significantly lower in trees occupied by O. smaragdina than in unoccupied palms. Similarly, the degree of foliar injury was significantly lower in occupied palms. There was a strong positive correlation between pest density and degree of foliar injury. The number of fruiting bunches, indicative of the palm-oil productivity, was significantly higher in occupied palms. The predatory behaviour of O. smaragdina towards P. pendula was confirmed by observations in a distinctive chronological sequence. Field experiments showed that O. smaragdina preferred to consume pupae over larvae (of all instars), until the extermination of the former. The study confirmed that O. smaragdina does not attack or disturb the oil palm pollinator weevil, Elaeidobius kamerunicus. The ant species thus shows great promise for biological control in oil palm.