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Study Reveals Ineffectiveness of Common Consumer Insecticides Against Cockroaches

A recent study published in the Journal of Economic Entomology indicates that popular consumer insecticide sprays are largely ineffective in addressing cockroach infestations, specifically highlighting their limited value in combatting the prevalent German cockroach (Blattella germanica).

The research, conducted by experts at the University of Kentucky and Auburn University, examined how well various residual insecticides function when applied to surfaces where cockroaches are likely to traverse. The results showed that these insecticides, typically formulated with pyrethroids, resulted in the death of less than 20% of German cockroaches after a 30-minute exposure on treated surfaces. Additionally, even when confined to these surfaces, the time taken for most products to kill the cockroaches ranged from eight hours to several days.

The cockroaches studied were sourced from actual infestations, where they have adapted to resist pyrethroids, supporting findings from previous research that highlighted this resistance in urban environments. Dr. Johnalyn Gordon, the study’s lead author, emphasized the implications for home environments, stating, “For those without access to effective pest control options, the health risks associated with cockroach allergens continue to pose challenges.” She argues that homes should be sanctuaries where individuals can take solace.

Dr. Gordon’s work was rooted in her time as a graduate research assistant at the University of Kentucky, working under the guidance of Dr. Zach DeVries, an expert in urban entomology.

While cockroach control remains a feasible endeavor, the researchers stress that success often demands substantial time and financial investment in appropriate products. A significant hurdle in this battle is the widespread resistance of German cockroaches to pyrethroids, which has accumulated over years of product application. “The persistent use of these insecticides ensures that cockroaches in our homes develop some level of resistance,” Gordon noted. She further pointed out that it has been decades since any pyrethroid-susceptible populations have been identified in the field.

Interestingly, regulations from the U.S. Environmental Protection Agency do not mandate testing insecticide products on cockroaches collected from wild populations or those exhibiting resistance. “We hope that findings such as these will encourage modifications in testing protocols, enabling more accurate labels that reflect the products’ effectiveness,” Gordon stated.

Other factors likely diminish the efficacy of residual sprays, including the types of surfaces treated and cockroach behavior. The study monitored the performance of insecticides on various materials—painted drywall, ceramic tile, and stainless steel—discovering notably poor results on drywall. Even a non-resistant population of German cockroaches demonstrated minimal susceptibility on this surface.

Dr. Gordon highlighted that surface porosity significantly affects the effectiveness of insecticides, particularly where common applications—like along baseboards—are concerned. Furthermore, cockroaches typically avoid surfaces that are treated with insecticides, often limiting their exposure to these areas. Related research from DeVries’ lab suggests that resistant cockroach populations actively avoid contact with pyrethroid-treated surfaces when alternatives are available.

This multifaceted understanding of the issues surrounding cockroach control through insecticides reveals significant barriers to effective eradication. Gordon concluded, “Consumer-grade pyrethroid-based products are unlikely to be successful against German cockroaches in domestic settings, especially when used as residual solutions.” For more effective results, experts advocate for using gel or liquid baits, which attract cockroaches to a food source combined with a slow-acting insecticide.

Access to efficient pest management services employing an integrated pest management (IPM) strategy remains a challenge for many, particularly in low-income multi-family housing situations where cockroach problems are pervasive. “Despite extensive knowledge regarding effective cockroach management, economic and logistical barriers often inhibit solutions in these high-need areas,” stated Gordon.

She emphasized the necessity of enhancing pest control technologies that address these gaps, focusing on alternative active ingredients, different modes of action, and innovative strategies for product deployment.

More information: Johnalyn Gordon et al, Common consumer residual insecticides lack efficacy against insecticide-susceptible and resistant populations of the German cockroach (Blattodea: Ectobiidae), Journal of Economic Entomology (2024). DOI: 10.1093/jee/toae158

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phys.org