Effects of Dose, Donor-Recipient Interaction Time and Ratio on Fipronil Transmission Among the Formosan Subterranean Termite Nestmates (Isoptera: Rhinotermitidae)

transfer of fipronil’s lethal effect was studied against the Formosan subterranean termite, Coptotermes formosanus Shiraki. Donor workers were topically dosed with 2 different doses and placed together with recipient workers at 3 different donor-recipient ratios to observe recipient mortality at designed intervals for 20 days. recipients exposed to donors treated at10 ng a.i./donor yielded full expression of 90-100% mortality within 4 and 12 days at ratio of 1:1 and ≤ 2:8, respectively. recipients exposed to donors treated at 2 ng a.i./donor only showed < 48, 21, and 15.6% mortality at ratio of 1:1, 2:8, and 1:9, respectively, and the full expression of mortality appeared within 16 days. These results support the hypothesis that the time required for a full expression of transferable lethal effects of fipronil in untreated termites increases as the dose on treated termites decreases at given donor-recipient ratios. recipients exposed to donors treated with a high dose and at high donor-recipient ratio show greater mortality compared to those exposed to donors treated with a low dose and at low donor-recipient ratio. recipient mortality increases as the donor-recipient interaction time increases until full expression of transferred lethal effect. Donors had greater mortality than recipients at a given observation date before both donors and recipients reached 100% mortality.