Ethyl 2,4-dioxovalerate triggers aggregation and tunneling preference of Formosan subterranean termites (Blattodea: Rhinotermitidae) and enhances the effectiveness of fipronil.

Our previous study shows that Coptotermes formosanus (Blattodea: Rhinotermitidae) preferred to stay on filter paper treated with ethyl 2,4-dioxovalerate, a metabolite in the soil fungus Trichoderma virens. Here, we hypothesized that adding ethyl 2,4-dioxovalerate in sand could trigger aggregation and tunneling preferences of C. formosanus and improve the effectiveness of liquid termiticide. In aggregation-choice tests, significantly more termites were found on/in sand blocks containing ethyl 2,4-dioxovalerate (250 µg/g) than untreated blocks throughout the 24-h experiments. In the tunneling-choice tests, termites also excavated significantly more tunnels in the sand treated with ethyl 2,4-dioxovalerate (2.5, 25, or 250 µg/g) than untreated sand. However, in no-choice tests, ethyl 2,4-dioxovalerate (2.5, 25, or 250 µg/g) did not significantly affect tunneling activities, termite survival, wood consumption, or activities of detoxification enzymes (peroxidase, superoxide dismutase, and catalase) compared to controls. Interestingly, in aggregation- and tunneling-choice tests, termites preferred to stay and made more tunnels in sand treated with both ethyl 2,4-dioxovalerate (250 µg/g) and fipronil (1 µg/g) than untreated sand. In addition, in choice tests, sand treated with the combination of ethyl 2,4-dioxovalerate (250 µg/g) and fipronil (1 µg/g) caused significantly higher termite mortality than the sand treated with only fipronil (1 µg/g). Our study showed that ethyl 2,4-dioxovalerate may enhance the effectiveness of fipronil (1 µg/g in sand) by triggering aggregation and tunneling preferences of termites, thereby increasing the contact between termites and fipronil.