Your insecticide doesn’t do squat against cockroaches

Cockroaches — they’re as adaptable and resilient as hell. They can withstand the cold, heat, radiation, and lack of food; they may even survive a nuclear attack. Almost everything we throw at them, they can laugh it off. Thankfully, we’ve designed products specifically against them — products that can wipe out even the sturdy cockroaches.

Or so we thought.

According to new research, consumer-grade insecticides may have “little to no value” against cockroach infestations. Like some bacteria, cockroaches have become immune to the substances we throw at them.

Cocky and resilient

Cockroaches evolved in the Carboniferous period, some 320 million years ago — and they may never go away. Not only can they withstand all sorts of stuff nature throws at them, but they can even withstand the very substances made to kill them.

Specifically, they can withstand pyrethroid-based insecticides.

Pyrethroids are commonly used against cockroaches as they are potent insecticides. They work by affecting the nervous system of insects. But, due to the development of resistance in many cockroach populations, the effectiveness of pyrethroids has diminished over time.

Most insecticides are “residual” — they’re designed to be sprayed on surfaces where cockroaches are likely to appear. Cockroaches become exposed to the toxin residue while moving around and it kills them, at least in theory. However, researchers have shown that this has little effect on German cockroaches (Blattella germanica, also known as the Croton bug).

The team sprayed consumer-based insecticides and then exposed the cockroaches for up to 30 minutes. This killed less than 20% of the bugs. Even for cockroaches confined to a sprayed surface, it most products took 8 hours to kill the cockroach — some took more than 5 days.

A nuanced problem

Obviously, cockroaches are unlikely to stay still for hours and wait for the insecticide to work. In the real world, this would never happen. This means that regular folk have almost nothing that can stop cockroaches.

“If residents do not have access to effective professional pest control or consumer solutions, they continue to be impacted by the effects of an infestation, including the health risks associated with cockroach allergens. Home is where people should be able to relax and feel comfortable,” says Johnalyn Gordon, Ph.D., lead author on the study and a postdoctoral associate at the University of Florida.

The type of surface sprayed also made a difference. Gordon and colleagues tested several surfaces, including drywall, ceramic tile, and stainless steel. The worst-performing surface was drywall — even when researchers purposefully selected a cockroach population without resistance, the chemical had minimal effect.

“This suggests that how porous a surface is may have a significant impact on product efficacy,” Gordon says. “Given common applications of residual insecticides along baseboards, reduced efficacy on painted drywall was a particularly striking finding.”

The problem isn’t limited to one cockroach population. Researchers emphasize that virtually all these cockroaches exhibit a level of resilience. The bottom line is that common consumer-grade insecticides (which typically use pyrethroids) won’t stop a cockroach infestation.

“Due to the frequent use of pyrethroid-based residual products, it is very likely that German cockroaches inside of homes will have some degree of pyrethroid resistance,” Gordon says. “To the best of our knowledge, a pyrethroid-susceptible German cockroach population has not been documented from the field in decades.”

So, what can you do?

The first problem is that consumers have been misled into believing this type of product will actually help. At least in the US, the Environmental Protection Agency (EPA) doesn’t even require testing on recently collected cockroaches, let alone cockroaches with demonstrated insecticide resistance.

“Hopefully studies like this one can drive changes in product testing and evaluation, so that labels accurately reflect the level of control these products can provide,” Gordon says.

The other takeaway is that you need a different type of insecticide. This likely means calling a professional and asking for a deep clean and deep extermination using non-pyrethroid insecticides. So, if you’re facing an unfortunate infestation, call a professional and make sure they use stuff that the cockroaches aren’t resilient to.

At the very least, you should stop using pyrethroid insecticides against German cockroaches, because it doesn’t really do anything. You’re probably better off splatting them one by one.

The study was published in the Journal of Economic Entomology.