| Summary: | The red imported fire ant (<i>Solenopsis invicta</i>) is a worldwide invasive and dangerous insect that is controlled mainly by chemical insecticides. Plant-derived insecticidal compounds are generally better than synthetic insecticides for environmental compatibility and the biosafety of non-targets. The toxicity of the ethanol extract of <i>Sophora flavescens</i> roots against <i>S. invicta</i> was evaluated under laboratory conditions. The ethanol extract showed toxicity against minor and medium workers of <i>S. invicta</i> with 7-day LC<sub>50</sub> values of 1426.25 and 2292.60 mg/L, respectively. By bioactivity-directed chromatographic separations using the minor worker as the test insect, two active compounds, matrine and sophocarpine, were isolated from the <i>S. flavescens</i> total alkaloids; their chemical structure was identified by <sup>13</sup>C NMR data. Matrine showed toxicities against minor and medium workers with 7-day LC<sub>50</sub> values of 46.77 and 71.49 mg/L, respectively, and for sophocarpine, 50.08 and 85.87 mg/L, respectively. The two compounds could substantially reduce the foraging response, food consumption, and aggregation of <i>S. invicta</i> workers at a sublethal concentration of 15 mg/L. The present research suggests that <i>S. flavescens</i> roots have potential as a natural control agent for red imported fire ants.
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