German cockroaches are one of the most problematic insect pests to manage. They typically infest apartment buildings and multifamily homes, which can provide refuges for the population to recover after treatments. Population recovery usually happens quickly as roaches can have up to 6 generations per year. When an area is treated, roaches can often avoid encountering a lethal dose of insecticide by hiding in cracks and crevices. These characteristics of high reproduction rates and sublethal insecticide exposure have led to major resistance issues, especially when IPM and insecticide rotation are not being properly performed.
There are socioeconomic challenges to controlling this pest as well. German cockroaches are most problematic in low-income housing. Typically, in apartment settings, pest control contracts are bought so cheaply that a company cannot provide adequate control. In some situations, infestations can get out of control through the resident's failure to report it to management, due to fear of being blamed for causing a pest problem. Both situations can lead to many residents with German cockroaches resorting to repeated applications of consumer-grade pesticides to control the infestations themselves. These DIY products are considered inferior compared to the commercial products used the pest control industry.
Recent Study
A study out of the University of Kentucky set out to determine the control offered by many of consumer-grade, to understand the effectiveness of the DIY spray and aerosol treatments. The active ingredient in most off-the-shelf cockroach products are pyrethroids such as cypermethrin, lambda-cyhalothrin, and bifenthrin. German cockroaches have known resistance to pyrethroids, so mortality was expected to be diminished. The study measured the commercial products Raid Ant and Roach Killer, Hot Shot Roach, Ant and Spider Killer, Ortho Home Defense, and Spectracide Bug Stop, and the impact of direct, continuous, and limited exposures of these products to wild German cockroach populations.
Upon direct contact with the insecticide, only Ortho Home Defense consistently struggled to control treated German cockroaches. When exposed for a continuous period, Spectracide Bug Shop, and Hot Shot Roach, Ant, and Spider Killer performed well against roaches. The issue with these results is that applications often only contact a fraction of the cockroaches present, due to the instinct of the insect to hide. Continuous contact with a pyrethroid is also not probable, due to the slight repellent nature of the pyrethroids, which will cause a German cockroach to move through the insecticide rather than stay in contact with it. Limited exposure is therefore the most important component of a roach treatment. After limiting exposure to 30 minutes of direct contact, mortality of the wild German cockroach population was below 20% for all treatments tested, which is far from what is needed to provide adequate control.
Unfortunately, commercial-grade spray and aerosol products do not appear to offer adequate control for German cockroach populations. Due to the ability to kill on contact, many aspects of the treatments might appear to a resident applicator to be successful, but these products are not likely to treat the many unseen roaches that will continue to replenish the population. DIY cockroach gel baits are believed to have the potential to offer improved control over DIY sprays and aerosols, but these are still unlikely to provide the level of control offered by thorough professional intervention.
For more information check out:
Entomology Today. “Consumer-Grade Insecticide Sprays Fail to Control Cockroaches, Study Shows.” Entomology Today, Entomological Society of America, entomologytoday.org/2024/08/15/consumer-grade-insecticide-sprays-residual-pyrethroid-fail-control-cockroaches/.
Gordon, Johnalyn M, et al. “Common consumer residual insecticides lack efficacy against insecticide-susceptible and resistant populations of the German cockroach (blattodea: Ectobiidae).” Journal of Economic Entomology, 14 Aug. 2024, https://doi.org/10.1093/jee/toae158.
Pictured above: German Cockroach, female adult
Photo credit: Sarah Hughson, University of Illinois Urbana – Champaign
ABOUT THE AUTHOR: John Schepis provides subject matter expertise and training in pesticide safety with an emphasis on entomology.