Subterranean termite colony elimination can be achieved even when only a small fraction of foragers feed upon a CSI bait

Termite bait products that contain chitin synthesis inhibitors (CSIs) protect structures from subterranean termites via colony elimination. A hallmark of CSI baits is their dose-independent lethal time, as workers exposed to a CSI do not die until they initiate the molting process. Due to this mode of action and termite behaviors such as trophallaxis and cannibalism, a relatively small quantity of a CSI can spread throughout an entire colony before secondary repellency or avoidance behaviors occur, ultimately resulting in total colony elimination. In the field, only a portion of a subterranean termite colony actively forages upon a CSI bait at any given time, suggesting that only a relatively small proportion of workers may need to feed upon a CSI bait for the colony to be eliminated. In the present study, we used varying proportions of workers from whole four-year-old laboratory-reared Coptotermes gestroi (Wasmann) colonies (~62,500 termites/colony) to determine what proportion of workers need to feed upon a CSI bait in order to achieve colony elimination. We collected 0% (control), 0.5%, 1%, 2.5%, and 5% of the total worker population and allowed them to feed on a formulated 0.5% noviflumuron bait for 5 days before returning them to their colony. Colony elimination was observed for all 5%-fed and four out of six 2.5%-fed colonies by 107 days after CSI exposure. Our results suggest that only a small subset of the worker population of a colony must feed upon a CSI bait in order for the colony to be eliminated.