German cockroaches are one of the most common pests especially in places like affordable multifamily housing. They are not just unwanted house guests, but also a public health concern with their ability to mechanically vector pathogens and their allergens that have been shown to exacerbate asthma. And beyond the physical, the psychological impact of a cockroach infestation can be a difficult burden on folks as well.  

When housing management companies are not reliable and do not hire professional pest control services, individuals may turn to whatever products they can find at a store for direct spraying or residual use. Even those who do not face barriers to access professional pest control may opt to use store bought products as it may seem easier to try to do it themselves.  

Use of pesticides by residents has been studied and shown to be quite high.  in this experiment they studied consumer available products including direct sprays, limited exposure sprays (the kind you spray on a surface like countertops or painted drywall or tile), and continuous exposure. In all of these, the researchers were looking to find success as defined by 90% mortality (as stipulated by the EPA for a product to be able to claim it is successful) 

The researchers tested the products on a lab reared susceptible population, and three field collected populations from the past few years. The products used included Spectracide bug stop, Raid ant and roach killer, Ortho home defense, and Hotshot roach ant and spider killer.  

They found that direct exposure was the most effective route for each of the tested products. But even so, a total of 4 of 16 product-population combos failed to achieve the needed 90%.  This included the resistant field collected strains with Ortho home defense and the most recently field collected population with Hotshot.

 

 

Limited exposure was much less effective. They tested these population/product combos on different common household surfaces. The graphic here shows it pretty dramatically that across the board, painted drywall resulted in less than 20% mortality in all cases. the susceptible population had 100% mortality on ceramic tile and stainless steel across all products. The other field collected populations had less than 20% mortality across the board for all products and surfaces. 

The limited exposure studies are critical, because that is the best chance to hit the majority of the roaches, ones you do not see and at any time of the day. The mortality was shockingly low on painted drywall showing that is not a good surface to use the product on.  

The EPA regulations only stipulate that products must be tested on a population of German and American cockroaches but says nothing about them being recently field collected. This study proves that field collected strains from years ago and more recently are resistant against these products. The researchers make the argument that it is critical for products labeled for use on cockroaches to be tested using populations with known pyrethroid resistance.  

The researchers recommend people to choose a gel bait or better yet, seek professional pest control. The potentially high cost for professional services can be a barrier to those in low-income housing. There will always be people who for whatever reason try to do pest control themselves. Products on the market should be effective to field populations according to packaging claims. With this study, this is not true across the board. 

Article by: Ellie Sanders, BCE-Intern

References

Johnalyn M Gordon, Marla J Eva, Sudip Gaire, Arthur G Appel, Zachary C DeVries, Common consumer residual insecticides lack efficacy against insecticide-susceptible and resistant populations of the German cockroach (Blattodea: Ectobiidae), Journal of Economic Entomology, 2024;, toae158, https://doi.org/10.1093/jee/toae158  

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