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Dead cockroaches
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The Gray Zone of Insecticide Repellency: Revisiting Long-Held Assumptions About Pyrethroid Effects on Pests

By Alvaro Romero, Ph.D.
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Dead cockroaches

Insecticide efficacy is often equated with direct mortality — but that’s only part of the story. Some compounds, especially neurotoxic insecticides like pyrethroids, produce sublethal effects that disrupt pest behavior and physiology without causing immediate death. These responses may include irritancy, hyperactivity, avoidance, mating disruption, or interference with aggregation and feeding behavior. Sublethal exposure could impact a pest’s ability to mate and pass on its genes. While the pest may be alive, the product has “removed” the pest from their ultimate biological goal of reproduction.

In mosquito control, sublethal exposure to pyrethroids can trigger behavioral changes — either through detection of insecticides at a distance (repellency) or agitation after contact (irritancy) —both of which can reduce human-vector contact. While these categories often overlap, it is useful to distinguish between them: repellency involves sensory-driven avoidance without contact, typically mediated by olfactory receptors in the antennae, whereas irritancy results from neurotoxic effects that provoke escape responses after contact.

Among these sublethal responses, spatial repellency plays a particularly important role in mosquito management. Volatile insecticides delivered via spatial sprays or emanators create an airborne barrier that discourages mosquitoes from entering or remaining in treated areas. For pests such as termites, ants, cockroaches, bed bugs, and other occasional invaders, sublethal responses to insecticides are often viewed as problematic. It is commonly—but incorrectly—assumed that these pests can reliably detect and avoid treated surfaces. In reality, predictable and consistent repellency is primarily observed in subterranean termites. Although ants are often believed to avoid insecticide-treated areas, studies show that they typically continue foraging over such surfaces, suggesting that true repellency does not apply. For most other pests, behavioral responses to insecticides vary depending on species, physiology, environmental context, and product formulation. Below, we explore how these sublethal effects influence outcomes for key urban pests when exposed to pyrethroids.

Not So Repelled: Why German Cockroaches Still Cross the Line

German cockroaches offer a compelling example of how sublethal insecticide effects can challenge traditional assumptions about repellency. Pyrethroids are widely considered to provoke strong and predictable behavioral responses, including repellency. However, recent studies under controlled laboratory conditions have demonstrated that German cockroaches still make contact with pyrethroid-treated surfaces—contradicting the common belief that these compounds are strongly repellent. This finding is consistent with the low volatility of many pyrethroids, which limits their potential to exert true spatial repellency. These observations have led to the suggestion that placing cockroach gel baits on or near pyrethroid-treated surfaces may not diminish bait effectiveness, as cockroaches appear to continue foraging over treated areas. While contact with pyrethroids can produce an irritant effect that prompts temporary retreat or relocation to untreated zones, cockroaches often resume nocturnal activity and may re-encounter treated surfaces or nearby baits, resulting in continued exposure. More research is needed, particularly on formulations that combine neonicotinoids with pyrethroids, to better understand how these chemistries interact to influence contact irritancy, avoidance behavior, and foraging dynamics in cockroaches under both laboratory and field conditions.

Termites: A Distinct Case of Ground-Level Repellency

Termites are one of the few pest groups that consistently demonstrate true repellency to some insecticides—especially pyrethroids like permethrin, bifenthrin, and cypermethrin. Numerous studies have shown that subterranean termites actively avoid soil treated with these compounds, altering their tunneling behavior or abandoning the area entirely. This reliable avoidance response plays a key role in forming chemical barriers that protect structures by preventing termite entry. Because of this consistent behavior, pyrethroid-based termiticides have long been marketed and used as repellent soil treatments, in contrast to non-repellent options like fipronil or imidacloprid, which termites unknowingly traverse, enabling colony-level suppression through horizontal transfer.

Ants: A Case Where “Repellency” Doesn’t Apply

The commonly held belief that pyrethroids always act as repellents has been challenged in ants, with research showing that foraging individuals do not actively avoid pyrethroid-treated surfaces. Although ants are highly sensitive to chemical cues and communicate extensively through pheromones, studies have demonstrated that ants continue to behave normally—following trails and foraging—even after stepping onto treated areas. The perceived “repellency” in some cases likely results not from active avoidance, but from the insecticide killing foragers before trails are firmly established. Field trials, such as those involving Argentine ants and bifenthrin-treated panels, further support this: ants continued to cross treated surfaces and died within minutes, without evidence of behavioral avoidance. These findings suggest that pyrethroids can be used effectively against ants in perimeter applications, provided formulations are applied strategically to zones of activity.

A similar response might be expected in other occasional invaders—such as scorpions (Fig. 1), stink bugs, lady beetles, boxelder bugs, ground beetles, earwigs, crickets, and sowbugs—which often move along treated structural edges and surfaces both around buildings and when entering indoor spaces. While further research is needed to better characterize the behavioral responses of these pests to pyrethroid-based formulations, leveraging the contact-based exposure observed in ants could improve the overall effectiveness of insecticide applications in both indoor and outdoor general pest management programs.

Conclusion: Rethinking Repellency in Pest Control

The idea that pyrethroids universally repel pests is an oversimplification. As this review shows, true and predictable repellency is largely limited to subterranean termites, whose soil-foraging behavior makes them uniquely sensitive to pyrethroid-treated zones. For other pests—including ants, cockroaches, bed bugs, and occasional invaders—behavioral responses to pyrethroids are far more nuanced. Many species do not actively avoid treated surfaces, and in some cases, sublethal effects such as agitation or increased mobility may even enhance exposure to insecticides or drive pests toward strategically placed control tools like baits or dusts.

Recognizing the complexity of these sublethal responses is essential for developing effective, pest-specific strategies. Rather than treating repellency as an all-or-nothing phenomenon, pest management professionals should consider how formulation type, application strategy, and environmental context influence pest behavior. When approached thoughtfully, sublethal effects—often seen as limitations—can instead be leveraged as assets, helping to improve outcomes across a range of urban pest control programs. This may be especially true for occasional invaders, where non-repellency can promote greater contact with treated surfaces and increase the likelihood of effective control.

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References

  • Haynes, K. F. (1988). Sublethal effects of neurotoxic insecticides on insect behavior. Annual Review of Entomology, 33, 149–168. https://doi.org/10.1146/annurev.en.33.010188.001053
  • Moore, D. J., & Miller, D. M. (2006). Laboratory evaluation of insecticide product efficacy for control of Cimex lectularius. Journal of Economic Entomology, 2080–2086.
  • Romero, A., Potter, M. F., & Haynes, K. F. (2009). Behavioral responses of the bed bug to insecticide residues. Journal of Medical Entomology, 46, 51–57.
  • Thanispong, K., Achee, N. L., Bangs, M. J., Grieco, J. P., Suwonkerd, W., Prabaripai, A., & Chareonviriyaphap, T. (2009). Irritancy and repellency behavioral responses of three strains of Aedes aegypti exposed to DDT and α-cypermethrin. Journal of Medical Entomology, 46, 1407–1414
  • FMC Australasia. (2021). Repellents vs Non-Repellents: It’s Not All Black and White. FMC Corporation educational brochure. © FMC Australasia
  • Romero, A., Agnew, J., Paysen, E., & Blakely, B. (2021, October 19). Arizona bark scorpions and their responses to insecticides. PCT Convention Extra 2021. https://www.pctonline.com/article/arizona-bark-scorpions-and-their-responses-to-insecticides/
  • Gaire, S., Gondhalekar, A. D., & Scharf, M. E. (2024). Behavioral responses of field‐collected German cockroaches to pyrethroids and implications for resistance management. Pest Management Science, 80, 4323-441.

 

Frank Meek, Orkin
Bug Bytes

How to Keep Pathogen-Spreading Pests Out of Your Business

By Frank Meek
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Frank Meek, Orkin

As food processors and retailers work tirelessly to feed the public during the current global health pandemic, pests continue to work overtime to keep their food supply on track. Filth flies, cockroaches and rodents, in particular, pose a threat to the food supply chain, especially with concerns of the transmission of pathogens at an all-time high. The last thing your business needs is an avoidable food safety incident that threatens your reputation and bottom line.

When it comes to food safety, pathogen-spreading pests have no place in your facility and pose a major public health risk. Not only can these filthy pests become a nuisance within your facility, they can also contaminate your products and spread foodborne bacteria such as Salmonella, E. coli and Listeria, which can cause illnesses.

Knowing what attracts these pests to your facility and the dangers they pose is important for effective removal. Let’s dive into the signs of cockroaches, filth flies and rodents, and the specific concerns they can cause.

Frank Meek will share his expertise during a complimentary  webinar on March 4, “Making the Grade: Tips for Passing Food Safety Audits During the Pandemic” Cockroaches

Cockroaches seek four things that food processing facilities provide in abundance—food, shelter, proper temperatures and water. With the ability to squeeze through tiny gaps and cracks, these dirty pests enjoy crawling under equipment, in cabinets and through drains to find their next meal. Cockroaches can be found in and around almost any place within your facility. They’re capable of carrying harmful bacteria that they can spread from one location to another. Look out for droppings, cast skins or egg cases, which might signal a cockroach problem.

Filth Flies

You may think these types of flies have no desire to be inside, but they are in fact happy to go wherever the conditions are right. The most common filth fly is the housefly. These winged pests can carry and spread more than 100 disease-causing pathogens including bacteria, fungi and viruses. These can cause illnesses such as cholera, dysentery and infantile diarrhea. Filth flies in your facility can lead to a major public health issue if your food becomes contaminated.

Rodents

One of the filthiest pests around, rodents can contaminate your food supply, destroy or consume products and cause structural damage to your facility. Like cockroaches, mice and rats can fit through relatively small spaces to find food and water. With sightings on the rise during the COVID-19 pandemic, you’ll want to keep an eye out for rodents near your food products. These mighty chewers pose a public health threat as they can transmit diseases such as hantavirus and lymphocytic choriomeningitis (LCM) via their urine and droppings.

The presence of these vermin in your facility threatens public health. Additionally, an infestation can slow down the supply chain by causing businesses to recall contaminated foods.

A rigorous sanitation routine is one of the most effective ways to proactively manage pests like cockroaches, rodents and filth flies. Regularly sanitizing and disinfecting your facility can help eliminate any pathogens left behind on hard surfaces and remove the attractants for which they search. While cleaning removes dirt and buildup, sanitization and disinfection kill bacteria and pathogens, reducing the risk of a food safety issue.

Including the following tips in your cleaning routine can help keep your products and reputation safe from harm.

  • Clean out drains routinely with an enzymatic cleaning solution that can break down the organic grime.
  • Disinfect high-touch hard surfaces with a proper and low-toxicity disinfectant to kill bacteria and pathogens that can cause food illnesses.
  • Move dumpsters away from your building to reduce flies being attracted to and then gaining easy entry into your facility.
  • Wipe spills as soon as they occur to prevent them from becoming a sticky paradise for flies and cockroaches.
  • Practice good hygiene in your work environment and ensure employees are washing their hands regularly and keeping break rooms free of trash and leftovers.

Implementing exclusion practices such as sealing cracks, gaps and holes in walls with a proper sealant can also help you keep pests out. Budget allowing, consider investing in insect light traps and mechanical traps to help reduce flying insects inside.

Communication with your suppliers and distributors is also important to ensure food safety. If your partners implement similar measures, you’re more likely to protect the public from harmful diseases. Furthermore, customers will continue to trust your business.

While following these tips can help reduce the chances of a pest infestation, it’s not always possible to keep pests and the pathogens they spread out of your food processing facility. Work with a trained pest control specialist to develop a customized prevention program for your business as each type of pest requires specific treatment. They can also help you schedule inspections to identify conditions in and around your facility that may attract flies, cockroaches and rodents, among other pests.

Ron Harrison, Ph.D., Director of Technical Services, Orkin, LLC
Bug Bytes

Don’t Welcome Pests into Your Facility This Winter

By Ron Harrison, Ph.D.
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Ron Harrison, Ph.D., Director of Technical Services, Orkin, LLC

Days are now shorter, and temperatures are slowly dropping in most parts of the country. It is the time of year when individuals look to spend a little more time indoors and a little less time outdoors. However, did you know we aren’t the only ones looking for relief from the cold?

Similarly to us, this is the time of year when certain pests look for a nice, warm home to spend the winter months. The downside for food facilities is that they offer everything pests need for survival—food, water and harborage.

In fact, food facilities can face numerous pest challenges during the colder months, including ants, cockroaches, stored product pests and flies. Additionally, the most common and challenging winter pests are rodents. Due to their ability to squeeze through small spaces and adapt to many different environments, they can be a facility’s worst nightmare.

Don't let rats and mice threaten food safety audit scores. Image courtesy of Orkin
Don’t let rats and mice threaten food safety audit scores. All images courtesy of Orkin

The presence of rats and mice can lead to food contamination and can threaten your food safety audit scores, reputation and bottom line. Rodents are known carriers of deadly neurological and respiratory diseases like lymphocytic choriomeningitis virus (LCMV) and Hantavirus Pulmonary Syndrome. Ticks, mites and fleas can feed on infected rodents and transmit diseases like pox, plague and typhus indirectly to humans—putting not only employees in your facility at risk, but also customers.

Rodents can be tough to control and are very adaptable at living indoors. Some mice that take shelter inside due to weather can survive indefinitely as indoor mice. In fact, there is a possibility rodents may have already taken shelter by now, so it’s important to talk with your pest management professional about common areas where rodents may be hiding.

As you winterize your facility, it’s important to keep rodents and other pests in mind. A proactive approach to facility maintenance, as well as an effective Integrated Pest Management (IPM) program, can help keep pests out and your food product and business secure.

The following tips will help keep your facility off pests’ radars this winter.

Stay Vigilant in Monitoring for Pest Activity

Vigilant, ongoing monitoring is a cornerstone of an effective IPM program. With this strategy in place, there are many tactics you and your staff can use.

  • Identify “hot spots”. Work closely with your pest management professional to identify the most common places pests reside in around your property. These can include loading docks, utility rooms, employee break rooms, dumpsters and trash cans, storage rooms and behind any heavy, immobile pieces of equipment. By identifying these hot spots, you’ll be able to prevent pests from entering your facility.
  • Involve your employees. Educate your staff on the pests themselves, as well as the conditions that attract them, and encourage your employees to report any signs of problems. Utilize a reputable pest management company to provide your employees with this training—many providers offer training at no extra cost.
Look for gaps and fill them to keep those pesky critters out!
Look for gaps and fill them to keep those pesky critters out!

Strengthen Your Facility’s Perimeter

While certain pests can hitch a ride into your facility via shipments and even on people, the biggest pest threats start on the outside. With this in mind, you can take fight pests outside by strengthening your perimeter.

  • Look for and fill cracks and crevices. Crawling pests like to creep inside through small openings. Additionally, rodents can squeeze through holes the size of a quarter, mice through dime-sized openings that create gaps barely noticeable to the human eye. Regularly inspect the exterior of your facility for any cracks that may develop and pay close attention to openings that can form around pipes and utility penetrations. Don’t forget to seal any holes in exterior walls with water-resistant sealant and steel or metal mesh.
  • Eliminate clutter and attractants. Rodents may burrow or live up to 100 yards away from your structure, and flies, ants and cockroaches are also on the hunt for easy meals that can often be found on the property. Keep trash handling areas free of clutter, and clean up any uncovered garbage or standing water outside. Also, work with your waste management company to ensure they clean and switch out dumpsters regularly.
  • Keep landscaping off your building. Pests will often use vegetation as staging and feeding sites.  Keep trees trimmed and plants at least 12 inches from your building, and remove leaves quickly so pests cannot use them for cover. As an extra step, consider installing a two-foot wide gravel strip around the perimeter of the building. Think of these exclusion techniques as digging a moat around your castle.
  • For rodents, bait stations can be set outside. Work with your pest management provider to place tamper-resistant bait stations around the exterior of the facility. However, do not place the stations near doors or entryways, as they can attract pests into the facility. Be sure to maintain an up-to-date map of bait stations and record activity at each station to determine the source of rodent pressure and target future treatments accordingly.
Prevent fruit flies by keeping employee break rooms clear of food remnants and tightly sealing garbage cans.
Prevent fruit flies by keeping employee break rooms clear of food remnants and tightly sealing garbage cans.

Reinforce Clean Conditions Inside

Once you set up an outside defense against pests, you can double down on your pest management efforts by taking a few proactive measures inside as well. The key to keeping pests from infesting your facility is removing incentives for them to go inside in the first place.

  • Inspect incoming shipments. When you are not receiving materials, keep loading bay doors closed—make sure the doors close securely so that pests cannot sneak under them. Inspect incoming raw materials, packaging and truck trailers for signs of infestation.
  • Reduce potential food sources inside your facility. Employee break rooms should be clear of any food remnants, and garbage cans with food and other waste need to be kept tightly sealed.
  • Monitor the plant floor. Sanitize drains and equipment with an organic cleaner to eliminate the residue that pests can feed on. With colder temperatures, pipes can break or crack, so ensure plumbing is also maintained properly to prevent leakage and property damage. Monitor for spills and clean them immediately, as pests only need a small amount of moisture to survive.

By putting proactive defenses into place, your facility can enjoy the winter seasons with a decreased likelihood of the appearance of unwanted visitors like rodents, ants, cockroaches, stored product pests and flies. Talk with your pest management professional about these steps and other tactics you can put in place to keep your facility safe against overwintering pests and relegate them to the cold.