Herbal plants as alternatives for the management of the red imported fire ant, Solenopsis invicta

The red imported fire ant (RIFA) is one of the most detrimental invasive species, threatening native ecosystems, human health and economic activities worldwide. In the quarantine zone of Taiwan, RIFA re-infestation frequently occurs despite the intensive application of synthetic pesticides, making its control costly and ineffective. Thus, there is an urgent need to identify eco-friendly and sustainable alternatives for controlling RIFA populations. This study examined the efficacy and feasibility of planting herbal species for RIFA control. Five herbal species, Tagetes lemmonii, Armoracia rusticana, Cymbopogon citratus, Cymbopogon nardus and Chrysopogon zizanioides, were grown in a RIFA-infested field with local weeds as controls. Bait and pitfall traps and RIFA-intruded plants were used to compare the ant activity in the control fields and those containing herbal plants. We further evaluated the RIFA repellent activity of the five herbal plants and their basal soil through digging bioassays. Generally, the field surveys showed more ants and intruded plants in the control than the herbal groups; however, the significance varied based on the trap type and plant species. The digging bioassays demonstrated that the aboveground parts of T. lemmonii, C. nardus, C. citratus and the belowground parts of T. lemmonii, C. citratus and C. zizanioides effectively repelled RIFA. The basal soil of T. lemmonii, C. citratus and C. nardus also exhibited deterrent activity towards RIFA. Our results demonstrated that herbal plants are eco-friendly, sustainable alternatives for controlling and preventing RIFA infestation in severe infested and non-infested areas. © 2022 Wiley-VCH GmbH.