Insecticidal and Repellent Activity of Piper crassinervium Essential Oil and Its Pure Compounds Against Imported Fire Ants (Hymenoptera: Formicidae)

<i>Piper crassinervium</i> Kunth (Piperaceae) essential oil (EO) was evaluated for its toxicity and repellency against red imported fire ants (RIFA), <i>Solenopsis invicta</i> Buren, and a hybrid (HIFA) of red (<i>S. invicta)</i> and black (<i>S. richteri</i> Forel) imported fire ants. Through bioactivity-guided fractionation, two major components, elemicin and myristicin, were isolated from the EO. Removal of treated sand in a digging bioassay was used as the criterion for repellency. The EO showed significantly higher repellency at concentrations of 7.8 µg/g against RIFA and HIFA workers, as compared to the DEET (<i>N</i>,<i>N</i>-diethyl-<i>meta</i>-toluamide) or ethanol control. 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 failed at 31.25 µg/g against RIFA and 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 was more toxic against RIFA and HIFA with LC₅₀ values of 54.3 and 35.3 µg/g, respectively. Elemicin showed 20-40% mortality at the highest screening dose of 125 µg/g. Fipronil exhibited the highest toxicity against RIFA and HIFA, with LC₅₀ of 0.43 and 0.51 µg/g, respectively. Different formulations of these natural products should be evaluated to explore their use potential under natural field conditions.