Piper crassinervium essential oil: Toxicity and repellency against imported fire ants (Formicidae: Hymenoptera)

Piper crassinervium Kunth (Piperaceae) essential oil (EO) was evaluated for its toxicity and repellency against red imported fire ants (RIFA), Solenopsis invicta Buren, black imported fire ants (BIFA), Solenopsis richteri Forel, and hybrid imported fire ants (HIFA). Elemicin and myristicin were the major active constituents of the EO. Concentrations ranging from 125 µg/g until the failure of treatment were evaluated. The amount of treated sand removed in a digging bioassay was used as the criterion for repellency. The EO showed significantly higher repellency at concentrations of 7.8, 3.9, and 7.8 µg/g against RIFA, BIFA, and HIFA workers, respectively, as compared to control. Elemicin and myristicin were tested only against HIFA and RIFA. Elemicin exhibited repellency at 3.9 and 7.8 µg/g against RIFA and HIFA workers, respectively, whereas myristicin was active at 7.8 µg/g against both species. DEET (N,N-diethyl-meta-toluamide) failed at 31.25 µg/g against RIFA and at 15.6 µg/g against HIFA. The EO showed LC50 values of 97.9 and 73.7 µg/g against RIFA and HIFA workers, respectively. Myristicin with LC50 values of 54.3 and 35.3 µg/g against RIFA and HIFA, respectively, was the most active compound. Elemicin only caused 20-40% mortality at the highest testing dose of 125 µg/g. Bifenthrin, a commonly used pyrethroid, with LC50 of 0.29 and 0.18 µg/g was most toxic against RIFA and HIFA, respectively. The EO and the pure compounds showed toxicity and repellency against imported fire ants. Different formulations of these natural products should be evaluated to explore their use potential under natural field conditions.