What is a recommended chemical control method for the American cockroach?

Placing residual baits in cracks and crevices is effective for controlling the American cockroach due to their behavior and habitat preferences. Residual baits contain an active ingredient that remains effective over time, allowing for prolonged exposure to the pest. American cockroaches tend to hide in dark, damp areas, making cracks and crevices ideal locations for placement. When the roaches come into contact with or ingest the bait, it leads to their elimination and helps in controlling the population inside structures.

The other methods mentioned have limited effectiveness. Using traps and barriers might help catch a few individuals but does not address the broader infestation. Spraying insect growth regulators outdoors is more useful for preventing the development of immature stages rather than controlling adult populations already present. Applying natural repellents near food sources may deter some cockroaches momentarily, but it does not provide a long-term solution or reduce existing populations effectively. Thus, the use of residual baits is the most reliable approach among the options provided.