It’s a late night, well after dinner, and you take a stroll into your kitchen for your pre-bed snack. As you turn on the light you swear you see something run across your kitchen counter. Walking closer you realize that there, in plain view, on the surface where you just prepared your dinner, a small tan insect with two dark stripes on the back of its head stares back at you. You have just stumbled onto an unsuspecting (and apparently unbothered) German cockroach (Blattella germanica) (Figure 1). Your first thoughts may be: “Where did it come from?” or “Are there more?” or even “Am I going to have to burn my house down?” To answer those questions – it’s hard to know for certain; yes, there are most likely more, and absolutely not! German cockroaches, like all other structural pests, can be effectively managed and eliminated if the correct steps are taken. In this publication, we will provide you with an overview of German cockroach management, the do’s and don’ts, and the information needed to consult and hire a professional pest management company. So, take a deep breath, grab that snack you came into the kitchen to get, and read on to learn more.

Figure 1. A gravid female German cockroach (Blattella germanica) with an ootheca (egg case) protruding from her abdomen.

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Figure 1. A gravid female German cockroach (Blattella germanica) with an ootheca (egg case) protruding from her abdomen.

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As with any pest, there are certain clear signs that can indicate the presence of an active and ongoing German cockroach infestation. While professional pest management companies train their employees to recognize and identify these signs, it is important for home- and business owners to also be aware of them. Some of the most common signs of German cockroach infestation are:

1. Feces: One of the most common signs of German cockroaches is the presence of feces – or fecal spots – in tight and or concealed areas around food storage and preparation areas. These feces appear as clusters of tiny dots, ranging from brown to black in color, and will remain in the environment and on surfaces for long periods of time (Figure 2). The amount of feces in an area can serve as an indicator of population size but is not the most reliable method of determining this. Feces can also be removed via thorough cleaning (and potential scraping where appropriate), but protective masks and gloves should be used.

2. Cockroaches: Aside from feces, most folks realize that cockroaches have moved into their home by stumbling upon either a live or dead cockroach (Figure 1). Typically, German cockroaches prefer dark and warm areas of high humidity within close proximity to food and water sources. These can include areas in the kitchen (dishwasher, refrigerator, cabinets) or areas outside of the kitchen where all of the necessary resources are available (washing machine, coffee machine, pantry). Inspect these areas periodically if you suspect or know that German cockroaches have entered your property. See below for suggestions on passive monitoring.

3. Other Signs: These signs are generally considered “uncommon” given the unique biology and behavior of the German cockroach – which you can read about in Biology and Behavior of The German Cockroach. These include exuviae (shed exoskeletons), oothecae (egg cases), a specific odor associated with heavy infestation, and even occasionally signs of nibbling activity from large numbers of cockroaches.

Human Risks

In general, the two greatest risks of German cockroach infestation are mechanical transmission of disease-causing agents and exposure to incredibly high levels of asthma-associated allergens in the environment. Briefly, it has been shown that German cockroaches are able to passively pick up and carry multiple diseases within their environments, including Salmonella. In terms of allergy production, their feces, shed exoskeletons, and saliva all contain varying levels of multiple allergens. As such, German cockroaches continuously deposit allergens into their environments if left unmanaged, and are one of the leading causes of asthma in young children. Read more about the potential risks of German cockroach infestation in Biology and Behavior of The German Cockroach.

Figure 2. A group of German cockroach nymphs surrounding a smattering of feces.

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Figure 2. A group of German cockroach nymphs surrounding a smattering of feces.

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German cockroaches are drawn to environments that provide warmth, humidity, food, water, and shelter. As opportunistic feeders, they are attracted to crumbs, spills, and garbage (Figure 3). Favoring warm, humid conditions, they often hide in dark, secluded spaces, such as garbage containers, kitchen cabinets, and spaces under sinks where food is potentially nearby.

A key factor in preventing German cockroach infestations is proper sanitation. In addition to reducing or eliminating potential food sources, practicing proper sanitation increases the effectiveness of cockroach baits. The less competing food sources there are, the more likely the cockroaches will feed on bait.

There are many steps you can take to reduce or eliminate potential food sources. Clean up all spilled foods, including crumbs on the floor. Do not let dirty dishes sit for too long. Dishes left unwashed are a major source of food for a kitchen infestation (Figure 4). Use tight-fitting lids on garbage containers to prevent cockroaches from accessing food sources. Keep areas around garbage containers. Dump sink strainers frequently to prevent food buildup. Keep countertops clean. Seal pet food tightly. Keep kitchen appliances such as toasters, microwaves, stoves, ovens, and refrigerators free of crumbs and other food debris. In addition, clean the areas around these appliances. Reseal all food after opening, place in a tightly sealed container, or store in the refrigerator.

Proper sanitation also includes preventing or eliminating potential water sources. Repair plumbing leaks, especially in kitchen and bathroom areas. Do not let water stand in sinks or bathtubs for long periods of time. Empty pans under refrigerators used to catch water from condensation. Avoid overwatering houseplants. Be aware that pet water bowls may be a source of moisture. Water condensation on pipes, under sinks, etc., may also be a source of moisture. Removing clutter, vacuuming, and sealing cracks and crevices will also help to make areas less conducive to German cockroach populations.

Figure 3. Male German cockroaches consuming peanut butter.

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Figure 3. Male German cockroaches consuming peanut butter.

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Figure 4. A kitchen counter covered in German cockroaches and feces

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Figure 4. A kitchen counter covered in German cockroaches and feces

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Alongside sanitation, and regardless of the presence or absence of signs of infestation, mechanical management (non-chemical) can be employed. In general this revolves around the strategic use and frequent checking/replacement of glue boards (Figure 5) or the practice of exclusion.

Glue Boards

These paper boards, which contain perforations that allow for boxing for added protection, are coated with a strong adhesive. This adhesive may be scented to further encourage cockroaches to interact with it and become stuck.

When deploying glue boards, make sure to place them in areas that make sense when considering German cockroach biology and behavior. This can include areas under and around sinks, stoves, pantries, or other similar conducive habitats. When placing these boards ensure that they are in areas where accidental contact is unlikely – as pets, children, shoes, and various items can inadvertently become stuck to the boards. In the event of accidental contact, do not rip the board off as this could cause damage, instead use a kitchen oil or baby/mineral oil to coat the stuck item/individual and gently massage the oil into the adhesive around the edge of the item. This will slowly work the stuck item/individual off of the adhesive.

Further, when deploying glue boards safely into areas of suspected German cockroach activity, be sure to place the boards along walls, intersections, and in corners. Cockroaches, similar to other pests, prefer to be in contact with as many surfaces as they can, and, as such, do not typically travel across open spaces unless approaching a food source.

Exclusion

Briefly, in single-family homes or single-occupancy businesses, the use of exclusion is unlikely to help eliminate or suppress a German cockroach infestation. This is due to the established aggregation already being present within the isolated structure. Exclusion becomes a useful tool in multi-unit residential and commercial settings. In this context, the German cockroaches may enter or move between units through adjoining walls, outlets, or in ceilings. If this type of movement or reintroduction is suspected, it is important to caulk or seal all possible ingresses into the structure. Doing so may not guarantee that movement between units doesn’t occur, but it will at least make the cockroaches work far harder to do so. These areas can also be treated with residual insecticides (i.e., dusts) prior to sealing for added protection. Prior to using any insecticide, be sure to read the label in its entirety and follow all directions, precautions, and restrictions. Applying any product in a manner inconsistent with its labeling is a federal violation.

Figure 5. A glue board correctly boxed and placed along an edge underneath a sink to monitor for cockroaches.

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Figure 5. A glue board correctly boxed and placed along an edge underneath a sink to monitor for cockroaches.

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Baits

Baits are very effective treatments for controlling German cockroaches. Pest management professionals have access to a wide variety of bait formulations, including gels, pastes, dry flowables, and containerized bait stations (Figure 6). Gels, pastes, or child-proof bait stations are available and especially useful to homeowners. In general, it is good practice to combine good sanitation practices with aggressive baiting to provide effective control of German cockroaches with minimal use of other insecticides, such as spray and dust formulations. However, it has been shown that heavy baiting programs, even in the absence of sanitation improvements, can provide substantial management of infestations. Be sure to read and follow all label directions, especially when using baits in areas where food is prepared or stored.

Baits are safe, easy to use, and highly effective when applied correctly and in the proper amount. Baits should be placed near or directly in places cockroaches hide, if possible. Cockroaches spend a large majority of their time in their harborages, so this will increase the chances of them feeding on the baits. In addition, this ensures the bait is inaccessible to children and pets. One reason cockroach baits are so effective is their ability to leverage secondary, or horizontal, transfer. Cockroaches naturally exhibit behaviors like coprophagy (feeding on the feces of other cockroaches) and cannibalism (feeding on each other). When cockroaches consume bait, the toxic effects can spread to others that ingest the feces or bodies of those initially exposed. This secondary transfer is particularly beneficial for targeting first-stage nymphs, which typically remain hidden in areas like wall voids or behind appliances and rely on coprophagy for nourishment. By utilizing these natural behaviors, cockroach baits can effectively reach and eliminate even the most elusive members of an infestation.

It is best to apply small placements of bait (i.e., pea size) in numerous locations as opposed to larger amounts in fewer sites. Be aware that it is often easy to apply too little bait where heavier cockroach populations are present. In such situations, a follow-up application one week later is a great idea to apply more bait where needed. Do not apply insecticide sprays in areas where baits are used because the sprays can repel roaches and prevent them from eating the bait. Do not over-apply baits in a single visit - it is better to apply bait over several visits than to apply bait in an unsafe or overexposed manner.

What if no suitable cracks exist for the application of gel bait? In this case, a small amount of bait may be placed in the crack of a folded piece of cardboard or wax paper. This may then be placed in tight areas, such as underneath refrigerators, between counters and a wall, or between appliances and cabinets/walls. Be sure to read and follow all label directions, especially when using baits in areas where food is prepared or stored.

Dusts

Dusts are best applied to dry, inaccessible voids for effective pest control. Avoid using dust in open areas, as they can become airborne and contaminate off-target sites or harm non-targets, such as people and pets. When using dust, remember that less is more. For optimal results, apply dust in a fine, even layer (Figure 7). Over-application, such as clumping or using excessive amounts, can deter cockroaches, as they perceive it as an obstacle and may avoid the treated areas altogether.

Kick panels on refrigerators and stoves may be removed so that dust may be applied underneath these appliances. Holes the size of the tip of a puff-type applicator can be drilled into the top of kick panels beneath cabinets, and dust may be applied through the holes to these areas. Dust may also be applied in the void space between the sink and wall, and around utility pipe penetrations.

Many insecticidal dusts, such as boric acid, diatomaceous earth, and silica gel, are effective against German cockroaches. However, it’s essential to use only products specifically formulated for insect control. Never use pool-grade silica gel for pest management, as it poses a significantly higher inhalation risk compared to insecticidal silica gel. Always prioritize safety by choosing the correct product for the intended use.

Insecticidal Sprays

Although insecticidal sprays and aerosols can offer a quick and temporary knockdown of cockroaches, they do not provide long-term control and may even make the problem worse by repelling and dispersing cockroaches to other areas of the structure. Additionally, many cockroach populations have developed resistance to the insecticides commonly found in sprays and aerosols, reducing their effectiveness.

If insecticidal sprays are needed, they should only be applied in cracks and crevices and other voids German cockroaches may be hiding (Figure 8). This will ensure that the insecticide is delivered where the cockroaches are harboring and also reduces the likelihood of exposure to people, pets and undesired locations (e.g., countertops).

Total-release foggers, commonly known as "bug bombs," are ineffective for cockroach control because they fail to penetrate the crevices and hidden areas where cockroaches harbor and breed. Additionally, these products pose significant risks, including flammability hazards and potential health concerns from exposure to the chemicals released. Implementing an Integrated Pest Management (IPM) program can reduce or eliminate the need for sprays. An effective IPM approach combines proper sanitation and the strategic use of appropriate baits and dusts to achieve sustainable and lasting cockroach control.

Figure 6. A bait gun containing a tube of bait.

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Figure 6. A bait gun containing a tube of bait.

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Figure 7. A PMP applying dust into a void underneath a sink.

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Figure 7. A PMP applying dust into a void underneath a sink.

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Figure 8. A PMP applying a pressurized liquid insecticide into voids behind a baseboard

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Figure 8. A PMP applying a pressurized liquid insecticide into voids behind a baseboard

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Insecticide resistance in German cockroaches is widely documented and complicates the task of management and elimination. Insecticide resistance is defined as "a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species," according to the Insecticide Resistance Action Committee (IRAC). In other words, resistance could be occurring when a product repeatedly fails to control a pest, and the product is applied correctly and at the labeled rate.

This typically occurs within a population through repeated exposure to insecticides, where the strongest individuals survive. The cockroaches that survive are able to reproduce and pass on their resistant genes to the next generation. Over time, more and more of the population becomes resistant to the mode of action being used. As the process continues, the overall population becomes increasingly resistant, and the pesticide that once worked effectively starts to lose its effectiveness. In fact, German cockroaches are so effective at developing resistance that we have recorded resistant populations to every single class of insecticides used for their control since the 1950’s - that is concerning! But, all hope is not lost. New products utilizing multi-class chemistry, synergists, and even new modes of action are being developed to help combat resistance. However, you can help slow the spread as well!

One way to slow or prevent resistance is by rotating among varying modes of action periodically. A chart is provided by IRAC detailing the varying modes of action. This should be done at least every 3-4 months as a general best practice. Despite the concern of insecticide resistance in German cockroaches, it is important to not jump straight to resistance! Instead, take the following steps:

1. Confirm that the product was mixed and applied correctly at the appropriate rate.

2. Confirm that the product was not expired and that nothing tampered with or diluted the product after application.

3. Confirm that the product comes/came into contact with the cockroaches. This can be done in the office if collections are performed.

4. If needed, contact academic institutions to help in determining if resistance is occurring.

Bait Aversion

An additional point in German cockroach control is the emergence of glucose aversion. First reported from a field collected strain in Florida several decades ago, German cockroach populations are able to develop an aversion to glucose-sweetened baits. This occurs when the neurons that interpret taste shift to making sugar taste bitter. The result – glucose (and other more complex sugar containing baits) fail to eliminate the populations as bait consumption crashes. This is a major concern, as baiting is the most effective method of German cockroach control, and pest management professionals should remain vigilant. If you think glucose aversion is occurring, rotate to protein-based cockroach baits (MaxForce Granular) and contact research professionals for assistance and confirmation as needed.