Roaches transfer the bait through consumption or contact.
There are several ways in which cockroaches transfer bait to other cockroaches: through the eating of roach feces, roach regurgitation, consumption of dead cockroaches and their remains, and by contact. Nymphs (baby cockroaches) tend to stay in the nest and feed mainly on cockroach feces, making baits very effective in controlling the roach population. If a cockroach dies from eating roach bait, its carcass will contain enough insecticide to kill other cockroaches that feed on its remains. Dying cockroaches may also regurgitate and other roaches ingest insecticide in that way. Lastly, some insecticides, like Fipronil, can kill by contact. As cockroaches nestle together in the nest, they can transfer insecticide to one-another by contact.
How Combat Works to Eliminate Cockroaches:
The only sure way to eliminate cockroaches is to target them at the source. Unlike spray insecticides that kill the pests that come into contact with the spray, Combat roach baits have a domino like effect that kills roaches at the source. Combat baits are an effective cockroach insecticide disguised as a food source for roaches. Combat’s carbohydrate-rich formulation is a delicious mixture that is attractive to cockroaches. Once roaches ingest Combat, they return to their nests, where the bait is shared, further spreading the insecticide to the rest of the nest.