German cockroaches are most common cockroach in the world, one of the most notorious and resilient types of roach, and can produce allergens that worsen conditions like asthma. Unfortunately for humans, there have also been recent studies suggesting that these pests have also evolved resistance to the common, commercially available pesticides.
One such study specifically tested 5 common bait products using German cockroaches found in Southern California homes. The findings were discouraging; 4 of the 5 products were ineffective against the roaches, including 1 that failed entirely. It is believed that this is a “survival of the fittest” type of issue. The roaches that are immune to the pesticides are able to survive and breed more insects with the same resistance.
Other researchers have been investigating the use of essential oils to combat roaches and have found some success, but there does not seem to be definitive evidence that essential oils work as a cure-all. There have been some promising results in using limonene, which is found in bitter orange, orange, and grapefruit essential oils, as a roach deterrent, and carvacrol, which is found in oregano oil, as a pesticide. There are also many anecdotal reports of people finding success when using peppermint, rosemary, and eucalyptus oils. However, many essential oils are toxic to pets and are unlikely to completely rid your home of roaches when used alone.
So how should you handle roaches in your home? The general consensus is that the best method is something known as integrated pest management – combining multiple strategies and treatments to combat the issue. The local study mentioned did find that Optigard (0.1% emamectin benzoate) was the most effective treatment. Rotating multiple types of pesticides may be a good way to fight off the resistant bugs. You can also practice some basic home care habits, like paying special attention to common areas and attractions for roaches. One researcher suggests keeping kitchens and bathrooms clean and dry, as these are areas roaches are especially drawn to. Pet food is especially tasty to roaches, so it is also recommended to keep it in air tight containers when not in use and keep the bowls off the ground when in use.
Most of this information, including links to additional resources, came from National Geographic’s article titled “Killing cockroaches with pesticides is only making the species stronger” by Troy Farah.