Curcuma longa essential oils: toxicity and repellency against imported fire ants (formicidae: hymenoptera)

Authors: ALI, ABBAS - University Of Mississippi; SHAH, FARHAN MAHMOOD - University Of Mississippi; RADWAN, MOHAMED - University Of Mississippi; ELHENDAWY, MOSTAFA - University Of Mississippi; ELSOHLY, MAHMOUDA - University Of Mississippi; KHAN, IKHLAS - University Of Mississippi

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2023
Publication Date: 11/20/2023
Citation: Ali, A., Shah, F., Radwan, M.M., Elhendawy, M.A., Elsohly, M.A., Khan, I.A. 2023. Curcuma longa essential oils: toxicity and repellency against imported fire ants (formicidae: hymenoptera). Journal of Medical Entomology. 61,1, 191–200.
DOI: https://doi.org/10.1093/jme/tjad151

Interpretive Summary: Imported fire ants are significant pests, especially in the United States, known for their painful stings. Due to their aggressive behavior, fire ants have become a major safety concern for wildlife, agriculture, forestry, and ecological environments. Toxic baits and contact insecticides are used to manage fire ant populations and the repeated applications have resulted in behavioral adaptations to avoid mortality. Because of concern for potential environmental contamination, there has been increasing research interest in non-toxic natural products including secondary metabolites. Plant-derived natural products can offer a multitude of novel chemistries that can be effective repellents and toxicants. Curcuma longa L., commonly known as turmeric, is used in Indian folk medicines and is also popular in use in culinary and cosmetics. In our natural products screening program, C. longa leaf and rhizome essential oils demonstrated repellency and toxicity against mosquitoes and ar turmerone was the major compound responsible for this activity. This study evaluated the toxicity and repellency of C. longa essential oils against fire ant workers. Based on removal of treated sand in digging bioassay, which may directly be proportional to inhibition of digging ability of the fire ants, essential oils and ar-turmerone showed toxicity and repellency against imported fire ant workers. These natural products with repellency and toxicity play complementary roles. Repellency alters the digging behavior, and toxicity kills these. Further studies using different formulations of these natural products should be conducted to explore their use potential under natural conditions.

Technical Abstract: Curcuma longa L. (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 potential use of these natural products under field conditions.