Ineffective Bug Sprays: Struggling Against Persistent Roach Infestations with Store-Bought Repellents
Fighting Cockroaches Just Got Harder
Cockroaches have developed resistance to common pesticides, making the hunt for the persistent pest even trickier. A new study published recently reveals that store-bought roach sprays are largely ineffective in controlling infestations of German cockroaches in the wild, due largely to resistance to the pesticides that are most commonly used.
There are approximately 4,500 species of cockroaches, but only about 30 species live near humans, with a select few being persistent pests. These pest roaches aren't just annoying food stealers - they can also cause asthma attacks or spread disease. The most common pest roach that people encounter is the German cockroach (Blattella germanica). While roaches have a reputation for being invulnerable pests, they are surprisingly difficult to eradicate, and their survival skills have only improved over time.
Research has shown that today's pest roaches are increasingly resistant to pyrethroids, the most common class of pesticides used in consumer products. However, there's been surprisingly little research looking at how these products fare against real-world cockroach populations. In 2019, a study led by Zachary DeVries of the University of Kentucky found that total release foggers, also known as bug bombs, were largely ineffective against German cockroach infestations. DeVries and his team have continued to investigate the topic, and in their latest research, they put four common store-bought pyrethroid-based roach sprays to the test: Raid and Hot Shot aerosol sprays, as well as Ortho and Spectracide liquid sprays.
Combating Roach Resistance
The scientists tested the sprays on four different groups of German cockroaches: a lineage that had been isolated over 70 years ago, before being exposed to these pesticides, and three populations collected from recent infestations in North Carolina and Kentucky. The roaches were exposed under three conditions: directly spraying them, spraying common household surfaces such as tile or drywall and letting them dry, then keeping the roaches in place for 30 minutes, and maintaining them in place on sprayed surfaces for as long as it took for all the roaches to die. The latter two conditions were designed to mimic the sort of residual exposure that sprays leave behind.
The roaches isolated over 70 years ago were easily killed, but real-world cockroaches were more resilient. Many survived with limited exposure to the sprayed surfaces. "We found that there was some reduced efficacy with directly spraying the pyrethroid-resistant populations we tested," said Johnalyn Gordon, lead author of the study. "We also saw significantly decreased efficacy with limited exposure to those product residues on both porous and nonporous common indoor surfaces with our field-collected populations." Overall, these cockroaches only had an average 20 percent or less mortality rate under limited exposure. The findings were published in the Journal of Economic Entomology.
Directly spraying cockroaches in your sightline may kill them, but countless more lurking in the nooks and crannies of your home will escape. The team's earlier work has also shown that German cockroaches aren't likely to remain on sprayed surfaces for extended periods, waiting to die. Thus, the most common application of these products is likely to fail, and they are not entirely safe for people and pets since they contain toxic chemicals.
Breaking the Infestation Cycle
Given these findings and others, researchers suggest that people struggling with infestations should avoid spray products and instead opt for more effective methods. Professional exterminators who use a variety of control tools, such as integrated pest management, are particularly effective but often too expensive for many people. Store-brand roach gels and baits can effectively control a roach problem, especially if people rotate the products they're using periodically. These products can reach hidden clusters of roaches eager for a meal and are safer as well.
"Everyone deserves access to effective cockroach control and to live in a cockroach-free home, and products available and marketed for cockroach control should be able to control cockroaches," the researchers concluded.
Gordon will continue studying cockroaches and their close relatives, termites, at the University of Florida. She and her colleagues plan to study the real-world effectiveness of consumer roach baits in the near future.
Effective Alternatives for Roach Control
In addition to the products tested in the study, there are safer alternatives for residential and commercial roach control, such as:
1. Gel Baits
- Active Ingredient: Indoxacarb
- Description: Gel baits are applied in small dots or lines in areas where cockroaches frequent. Indoxacarb is palatable for cockroaches and disrupts their nervous system, leading to death. It remains effective over several generations, controlling the colony as a whole.
- Usage: Apply in areas inaccessible to pets, such as under appliances and in cabinets.
2. Food-Grade Diatomaceous Earth (DE)
- Description: Diatomaceous Earth (DE) is a silica powder derived from fossilized algae. It dehydrates and cuts cockroaches, causing death.
- Usage: Apply lightly in areas where cockroaches travel, including baseboards and behind cabinets. Although generally safe for pets, avoid excessive inhalation.
3. Insect Growth Regulators (IGRs)
- Description: IGRs disrupt cockroach development, leading to sterility and death. Once dried, they are generally safe for pets.
- Usage: Use IGR sprays that dry quickly or place IGR products in areas inaccessible to pets.
- The study revealed that store-bought roach sprays, such as Raid, Hot Shot, Ortho, and Spectracide, are largely ineffective against German cockroaches in real-world infestations due to their resistance to common pesticides.
- Researchers suggest that people struggling with infestations should avoid spray products like Spectracide and instead opt for more effective methods, such as professional extermination or the use of store-brand roach gels and baits.
- In the near future, Johnalyn Gordon and her team plan to study the real-world effectiveness of consumer roach baits, hoping to provide alternate, potentially more effective, solutions for cockroach control.
- In addition to the sprays tested, safer alternatives for residential and commercial roach control include gel baits with Indoxacarb, Food-Grade Diatomaceous Earth (DE), and Insect Growth Regulators (IGRs), which show potential for a wider range of control and less impact on human health.
