Photo by hhach from Pixabay
ANNAPOLIS, Md. — For decades, we’ve waged chemical warfare against cockroaches, confident in our superior firepower. But a new study is about to shatter that illusion, revealing that our trusted bug sprays might be little more than a minor inconvenience to these six-legged survivors.
Researchers at the University of Kentucky and Auburn University have delivered a wake-up call to homeowners and pest control professionals alike. Their study, published in the Journal of Economic Entomology, reveals that common consumer insecticide sprays are largely ineffective.
The German cockroach, Blattella germanica, is the cockroach equivalent of a supervillain – adaptable, resilient, and seemingly indestructible. These unwelcome houseguests have been the bane of apartment dwellers and homeowners worldwide, spreading allergens and potentially carrying pathogens. Now, it appears they’ve developed a new superpower: resistance to our chemical weapons.
The study focused on residual insecticides, those sprays designed to leave a toxic film on surfaces where cockroaches frequent. In theory, these products should turn your kitchen counter into a roach’s worst nightmare. In practice, they’re about as effective as laying out a welcome mat.
When researchers exposed field-collected German cockroaches to surfaces treated with pyrethroid-based sprays, the results were dismal. After 30 minutes of exposure, less than 20% of the roaches succumbed to the insecticide. Even more shocking, when cockroaches were confined to these treated surfaces – a scenario far more favorable than any real-world situation – most products took between 8 to 24 hours to finish the job. Some laggards took up to five days to achieve total roach annihilation.
“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 lead author Johnalyn Gordon, Ph.D., a postdoctoral associate at the University of Florida, in a statement.
The culprit behind this ineffectiveness? A combination of factors, with insecticide resistance leading the charge. German cockroaches have been battling pyrethroids – the active ingredients in many spray insecticides – for decades, and they’ve gotten very good at it. Gordon points out that pyrethroid-susceptible German cockroach populations haven’t been found in the wild for decades. Every time we spray, we’re essentially conducting an unintentional breeding program for super-roaches.
Adding insult to injury, the study found that surface type plays a crucial role in insecticide efficacy. Painted drywall, a common target for baseboard spraying, proved particularly ineffective at harboring lethal doses of the insecticide. Even cockroaches without pyrethroid resistance struggled to meet their maker on treated drywall surfaces.
How to get rid of cockroaches for good
But wait, there’s more! Cockroach behavior further compounds the problem. These cunning critters don’t lounge around on treated surfaces, sipping insecticide cocktails. They’re constantly on the move and may actively avoid areas that smell suspiciously of danger. A related study from the same research group found that resistant German cockroaches won’t stick around on pyrethroid-treated surfaces if given a choice.
So, what’s a frustrated homeowner to do? The researchers suggest that other strategies, such as gel or liquid baits, might be more effective DIY options. These products attract roaches to a tasty, but lethal, meal, which they then share with their colony mates. For more serious infestations, professional pest control services employing integrated pest management (IPM) techniques offer the best chance of success.
However, the study highlights a concerning gap in pest control accessibility, particularly in low-income, multi-family housing where cockroach infestations often run rampant. “There is a strong base of knowledge and research on how we can control cockroaches, but there are numerous economic and procedural barriers that mean that this control is not occurring in these areas, arguably where it is the most needed,” Gordon says.
According to the Entomological Society of America, another issue is that over time, insects and pests like cockroaches can also become resistant to some of the remedies intended to destroy them. “Unfortunately, repeated exposure of targeted insect pest populations to insecticides with the same biochemical mode of action—the specific biological pathway targeted by that chemical—can rapidly lead to evolution of resistance that reduces their effectiveness,” the agency sasys in a statement. “Insecticide resistance can develop in any situation where insecticides are used to control pests. The speed and degree to which resistance evolves in any population depends on an interaction of biological factors (the genetics, physiology, ecology, and behavior of target pests) and operational factors (the type of insecticide used, coverage achieved, and application timing, rate, and method).”
Bug spray overhaul needed
The implications of this study extend beyond just the annoyance of seeing a roach scurry across your floor. Cockroach infestations pose serious health risks, particularly for individuals with allergies or asthma. The continued use of ineffective products not only fails to address the problem but may also increase human exposure to potentially harmful chemicals without any benefit.
This research serves as a call to action for regulators, the pest control industry, and consumers alike. It underscores the need for more rigorous testing of insecticide products against field-collected, resistant insect populations before they hit the shelves. Currently, the U.S. Environmental Protection Agency doesn’t require such testing, potentially leading to a false sense of product efficacy.
“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.
In the meantime, the next time you reach for that can of bug spray, remember: you might just be giving those crafty cockroaches a refreshing shower rather than a lethal dose. The battle continues, but with science on our side, we may yet turn the tide in this age-old conflict.
Paper Summary
Methodology
The researchers conducted a series of tests using four common consumer-grade insecticide products against different cockroach populations. They performed direct contact tests, where roaches were sprayed directly with the products, and residual efficacy tests, where roaches were exposed to treated surfaces. The surfaces tested included ceramic tile, stainless steel, and painted drywall to represent different household materials. They also conducted continuous exposure tests, keeping roaches in constant contact with treated surfaces. The study used both a laboratory-raised susceptible cockroach population and several field-collected populations with varying levels of insecticide resistance.
Results
In direct spray tests, most products performed well, achieving high mortality rates. However, in limited exposure tests (30 minutes on treated surfaces), mortality rates for field-collected roaches were dramatically lower, not exceeding 20% on non-porous surfaces and even less on porous surfaces. Continuous exposure tests showed that it took at least 24 hours, and in some cases up to 5 days, to achieve 100% mortality in a field population. The study also found significant differences in effectiveness between susceptible and field-collected roach populations, with the latter showing much higher survival rates.
Limitations
The study focused on a limited number of products and cockroach populations. While it provides valuable insights, a broader range of products and more diverse cockroach populations could offer a more comprehensive picture. Additionally, the study was conducted under laboratory conditions, which may not fully replicate real-world scenarios where factors like temperature, humidity, and the presence of alternative food sources could impact insecticide effectiveness.
Discussion and Takeaways
The study highlights a significant gap between laboratory efficacy and real-world effectiveness of consumer-grade insecticide products against cockroaches. It suggests that the widespread use of pyrethroid-based products may be contributing to increased insecticide resistance in cockroach populations. The researchers emphasize the need for more rigorous product testing using field-collected, resistant insects before market approval. They also suggest that alternative control methods, such as baits or professional pest control services, may be more effective for managing cockroach infestations.
Funding and Disclosures
The study was supported by a grant from the U.S Department of Housing and Urban Development. The authors declared no competing interests.
For those who have not heard, a good way to kill cockroaches is to sprinkle 20 mule team borax around the area where they were found. 20 mule team borax is an inexpensive laundry detergent amplifier and it is relatively safe but you should keep it away from pets and children. It’s best to put it behind or under something so they can’t get to it.
Borax has the benefit that the roaches will carry it back to the nest and kill the entire colony, no poisionus sprays are necessary abd when the roaches are gone it is easy to remove the product with a vsccuum cleaner. The only down side is it may take up to a week to work.