Mortality Patterns in <I>Coptotermes gestroi</I> (Blattodea: Rhinotermitidae) Following Horizontal Transfer of Nonrepellent and Repellent Insecticides: Effects of Donor:Recipient Ratio and Exposure Time

The donor: recipient ratio and the time of donor exposure to termiticide required for maximal toxicant transfer among termites are crucial information for the development of termite management plans. Most of the available information on termiticide toxicity came from temperate zonal termite species, whereas little is known about tropical Asian species. In this study, mortality patterns of recipient termites, Coptotermes gestroi (Wasmann) subjected to seven formulated insecticide exposures under different donor exposure times and donor: recipient ratios were examined. For fipronil, lethal transfer was not affected by donor exposure time but was affected by the mixing ratio. The moderate-to-less toxic termiticides (imidacloprid, indoxacarb, bifenthrin, chlorfenapyr, and chlorantraniliprole) required long exposure time and a high mixing ratio to ensure maximal uptake by recipient workers compared with fipronil. For chlorantraniliprole and chlorfenapyr, donors must constitute > 30% of the donor-recipient mixture to achieve 100% mortality of the recipient workers. Among the termiticides tested, cyantraniliprole was the most fast-killing insecticide against C. gestroi. The potential of lethal transfer among recipient termites does not necessarily require both high donor exposure time and a high mixing ratio, but the toxicity of a given termiticide against termites must be factored in to achieve colony elimination.