Oecophylla smaragdina (Hymenoptera: Formicidae): A Biological Control Agent of the Invasive Bagworms Metisa plana (Lepidoptera: Psychidae)

Abstract The invasive bagworm Metisa plana Walker (Lepidoptera: Psychidae) is the dominant pest defoliator of oil palm canopies, leading to substantial leaf damage and monthly yield losses of up to 43%. Standard control methods involved trunk chemical injection (TCI) and spraying of highly toxic pesticides (such as cypermethrin) affecting non-target species. We hypothesized that the introduction of a biological control agent (BCA), the Asian weaver ant (Oecophylla smaragdina F.) (Hymenoptera: Formicidae), would outperform the TCI in scale and revenue consistency by controlling the bagworm population. A BCA colony was introduced with 20 brood nests translocated into four-hectare allocated experimental plots in Felda plantations, Peninsular Malaysia. To address the nuisances caused by BCA bites, we hypothesized that the essential tea tree oil (TTO) (Melaleuca linariifolia var. alternifolia) (Myrtales: Myrtaceae) repellency properties are a potent preventive measure. The assessment of ant-occupied palm trees shows an absence of foliar injury with higher quality fresh fruit bunches (FFB) and oil extraction rate (OER), contrasting with the high bagworm density in unoccupied, critically damaged canopies. BCA stands out as the most productive and lucrative, with more than triple the annual yield, incomes of any TCI group. Given the high correlation between yield variables and income, the polynomial regression showed accuracy in modeling BCA and TCI with minimal deviation between actual and predicted annual income. The repellent effect of TTO instantly neutralizes weaver ant aggressiveness, having an hour long lasting effect (first breakthrough report). Our findings suggest that O. smaragdina is an effective alternative to pesticide control treatment of bagworms.