Bistrifluron killed 95.7% of drywood termites that could still choose untreated wood

The summary at the top of UC Riverside's release and the body underneath it do not report the same measurement. The summary says the compound killed about 95 percent of colonies in testing ^[9]. The body reports 95.7 percent mortality among western drywood termites in controlled laboratory experiments in which they could choose between treated and untreated wood ^[1]. Colony elimination is the outcome a homeowner pays for; individual mortality in a feeding assay is what the experiment measured. A 95.7 percent kill leaves 4.3 percent of the termites in that test alive ^[2].

The choice test is the useful part of the design. Offer a slow-acting compound alongside clean wood and you learn whether the insects walk away from it. At 0.1 percent, bistrifluron killed about 99 percent of termites given no untreated alternative ^[3] and roughly 96 percent when an alternative sat next to it ^[4]. The gap is about three percentage points ^[1].

Bistrifluron is a chitin synthesis inhibitor: it interferes with the formation of the new exoskeleton a termite needs at its next molt ^[5]. Drywood termites molt about seven times during their lives ^[7]. "Once the termites reach a certain stage, they have to molt. They cannot avoid that," said Dong-Hwan Choe, the UCR entomology professor and senior author of the paper ^[10]. "With a lethal dose of this chemical, they'll try to shed their old exoskeleton but won't have a new one ready to protect them," he said ^[11].

Death comes late. The researchers first saw activity and feeding fall off, and the termites went on toward the next molt before failing it ^[15]. The 0.1 percent no-choice result was read at 60 days ^[3]. Nicholas Poulos, the paper's corresponding author and a doctoral student in UCR's entomology department, said of the compound, "It's specific to insects and can't harm humans" ^[13]. Chitin is widespread in nature; the release lists fungal cell walls, fish scales and the beaks of squids and octopi among the structures it builds ^[19]. Humans and other mammals have internal skeletons ^[18].

The experiments handed the termites treated wood. Finding the wood is the field problem: subterranean termites keep colonies connected to the soil, while drywood termites can live entirely within pieces of wood ^[17]. "It's been successfully used on subterranean termites, which are also important structural pests," Choe said ^[16]. The work reported here is laboratory work, and the release does not describe a field trial in an occupied structure ^[22]. "But native western drywood termites are also important, especially in California," Choe said ^[21].