There's a good reason a cockroach elicits a feeling of disgust when we see one scuttle past. Cockroaches carry a wide range of diseases and pathogens including bubonic plague, dysentery, hepatitis, hookworms, leprosy, salmonella and polio. It's understandable why, when someone sees a cockroach, they reach for the bug spray.
Yet new research suggests these consumer-grade pesticides don't really do much — and can even be harmful. According to a recent study in the Journal of Economic Entomology, one should think twice before using insecticides based on the organic compounds pyrethroids. This includes Raid Ant and Roach Killer, Outdoor Fragrance Free; Hot Shot Roach, Ant and Spider Killer; Ortho Home Defense Insect Killer for Indoor & Perimeter; and Spectracide Bug Stop Home Barrier. At best, they were all sporadically effective, depending on complicated circumstances, in killing a common cockroach species called German cockroaches (Blattella germanica.) Additionally, they can be dangerous for humans.
"While most products performed well when applied directly to test insects, mortality was substantially lower across all surfaces with limited exposure (30 min)," the authors write. "In continuous exposure assays on a nonporous surface, products took at least 24 hr to cause 100% mortality in a field population, with some products taking up to 5 [days] to achieve 100% mortality."
Johnalyn Gordon, PhD, a postdoctoral associate at the UF/IFAS Fort Lauderdale Research and Education Center, completed this work as a doctoral student at the University of Kentucky. Speaking with Salon, Gordon explained why German cockroaches were chosen for this study.
"German cockroaches have a couple of different qualities that make them very adept at surviving in our homes and being able to adapt to our pesticides and to our control strategies," Gordon said. "First of all, their small size. They can hide in a lot of different places. They also have a relatively short life cycle, so the populations are able to grow very quickly, almost exponentially within a home. And that also means you can get insecticide resistance in a population very quickly because that population is turning over and growing so fast."
Despite seeming like simple insects, cockroaches possess remarkable intelligence and diversity. Vanderbilt University cockroach researcher Terry Page famously observed that scientists who have observed many cockroaches tend to notice that "each cockroach has its own individual face. Each one is slightly different."
But for many people, such a face is something only a mother can love. Given roach resiliency, it is understandable why people might prefer the most extreme methods imaginable to get rid of these unwanted roommates. Yet Gordon urges people in these situations to focus on the long-term consequences of their possible responses.
"One of the biggest concerns with liquid or aerosol products, the ones that we tested in our study, and total release foggers, which have have been previously tested and found to be ineffective, is that they have the possibility to contaminate the indoor environment with large amounts of pesticides if they're used improperly," Gordon said. "And oftentimes they are. So if you're going to apply an entire can of Raid or set off six bug bombs or something like that in a home, it greatly increases the risk of pesticide exposure for pets or people living in that home."
As an alternative, Gordon suggests that people faced with cockroach infestations use baits.
"Gel baits have been found by numerous studies to be very effective, at least in the lab, for German cockroach control," Gordon said. "They have that added bonus that because they work through being consumed, there's a lot less pesticide that's actually being put into the home, and they can be placed in very targeted areas where they would be less accessible to members of the home."
By contrast, insecticide sprays containing pyrethroids are only somewhat capable of curtailing cockroaches. In one part of the experiment, the scientists introduced the cockroaches to a "limited" amount of exposure — meaning that instead of spraying them directly with the pyrethroid (which always killed them) or providing them with continuous exposure (regularly covering an area with the pesticide), they looked at situations where cockroaches were only occasionally exposed to the pesticide in question.
"For the limited exposure project, we were looking at individuals that were resistant to the active ingredient, which is pyrethroids," Gordon said." And we were also looking at laboratory susceptible populations of German cockroaches. The latter are ones that have been held in the lab for decades at this point. And so they haven't been exposed to any pesticides, including the particular pesticide we were looking at. So what we found in the limited exposure was that with those resistant populations that had been collected from homes, there was substantially lower mortality on those residues."
While cockroaches may not feel the sting of pesticides, humans might, especially if they are overused in the household. As the study authors put it, "Lack of efficacy of these DIY products can not only perpetuate the consumer’s feelings of hopelessness surrounding cockroach control, but increase desperation and lead people to misuse products, with disastrous results."
Side effects of pesticide exposure are generally considered low risk, but that depends on the level of exposure.
"Though considered to have low acute human toxicity, occupational exposure or accidental exposure through ingestion of pyrethroid insecticides may lead to dermal irritation, nausea and vomiting, and dizziness," the authors report. ":More recent studies have explored the negative impacts of prenatal and childhood pyrethroid exposure on neurodevelopment."
There are non-toxic alternatives to roach control. Diatomaceous earth, a powder made from fossilized diatoms, dries out the exoskeletons of roaches. Though one should avoid inhaling it, it doesn't contain any toxins, roaches can't develop resistance to it and it is often extremely effective at eradicating entire infestations. As a bonus, it also works against bedbugs, which are also evolving pesticide resistance.
In general, we need to reconsider how much pesticides we really need in our homes and how effective these products really are. The latest research is intended to make that easier — and safer — for consumers who live with infestations.
"One thing I want to highlight is that one of the biggest goals of this research was to provide some insights for people that are struggling with cockroach infestations," Gordon said. "We recognize that when it comes to the do-it-yourself products that are available on shelves, there's a wide variety of options that are available and we recognize that often resources are limited for people that are struggling with cockroach infestations in their homes. The goal of this project project was to provide some insights into how resources may can be allocated towards products that would be more effective at controlling cockroaches in homes."
