How Combat Plus Roach Killing Gel Works: Targets the nest and kills eggs. Easy to use. No vapor or fumes. For hard-to-reach places such as cracks or crevices. Roaches eat the gel and die in the nest. Other roaches eat them and die. How Combat Plus Quick Kill Formula Works: Starts killing in hours. For small roaches. Kills up to 6 months. Kills in hours. No vapor, fumes or odor. Child-resistant baits. Roaches enter the bait station and eat the bait. Roaches take the bait back to the nest. Roaches share the bait, killing other roaches and destroying the nest.