Curcuma longa essential oils: toxicity and repellency against imported fire ants (Formicidae: Hymenoptera)

Abstract

Curcuma longa L. (Zingiberales: Zingiberaceae) leaf and rhizome essential oils were evaluated for their toxicity and repellency against invasive fire ants: red imported fire ants (RIFA), Solenopsis invicta Buren, black imported fire ants (BIFA), Solenopsis richteri Forel, and a reproductively functional hybrid (HIFA). Ar-turmerone was the major constituent of leaf (42.4%) and rhizome (40.4%) essential oils. A range of concentrations starting from 156 µg/g until the failure of treatment were used. Removal of treated sand in digging bioassay was used as a criterion for repellency. Leaf essential oil showed significantly higher repellency at concentrations of 19.5, 9.8, and 4.9 µg/g against RIFA, BIFA, and HIFA workers, respectively, as compared with control whereas rhizome essential oil was active at 39, 19.5, and 4.9 µg/g against BIFA, RIFA, and HIFA, respectively. Ar-turmerone exhibited repellency at 19.5 µg/g against HIFA workers whereas DEET (N,N-diethyl-meta-toluamide) failed at 39 µg/g. Leaf essential oil showed LC50 values of 85.8, 97.7, and 182.7µg/g against RIFA, BIFA and HIFA workers, whereas the rhizome essential oil had LC50 values of 127, 109.9, and 151.2 µg/g against these species, respectively. Ar-turmerone, tested only against HIFA, with LC50 value of 57.2 was the most active compound. Bifenthrin, a commonly used pyrethroid, with LC50 of 0.03, 0.32, and 0.018 µg/g was toxic against RIFA, BIFA, and HIFA workers, respectively. Both the essential oils and ar-turmerone showed toxicity and repellency against imported fire ants. Different formulations of these natural products will be tested to explore the use potential of these natural products under field conditions.

Keywords: Curcuma longa; essential oil; imported fire ant; repellency; toxicity.