German Cockroach

Among the approximately 70 cockroach species found in the U.S., German cockroach, Blattella germanica (L.), is the most common due to its small size, short life cycle, and the ability to develop insecticide resistance. The German cockroach is distributed worldwide. They are found in homes, restaurants, ships, trains, aircrafts, hospitals, and many other types of modern indoor environments. This pest occurs more often in apartment buildings due to the building structural features that allow cockroaches to spread between units through common utilities, shared common walls, and hallways. German cockroaches contaminate food by transmitting pathogens. German cockroach feces, shed skins, and bodies of dead cockroaches contain allergens which are asthma triggers. Chronic infestations can pose significant long-term economic and public health costs.

Description

Egg

Eggs are carried in an egg case (ootheca), by the female until just before they hatch. The egg case can be seen from the posterior end of the female (Figure 1). A typical egg case contains about 40 eggs. It is about 5/16 inch long, 1/8 inch high, and 5/64 inch wide (8 mm by 3 mm by 2 mm). If the egg case is detached from the female, either manually or after exposure to insecticides, the egg case will typically not hatch unless it is within one to two days from hatching.

Nymph

The nymphal stage begins with egg hatch and ends with the emergence of the adult. Nymphs do not have wings. Their sizes range from 1/8 to 9/16 inch (3 to 14 mm). Nymphs molt 5–6 times before becoming adults. The stage between molts is called an instar.

Adult

The adult is ½ to 5/8 inch (13 to 16 mm) long, brown to dark brown in color. They are commonly identified by the two dark parallel stripes on their thorax. Males are slender and thinner with the posterior end tapered, females are wider and thicker with the posterior end rounded.

Behavior and Life Cycle

The German cockroach is omnivorous, eating a wide range of human foods, pet food, fruit, leather, and even book bindings. They also feed on the dead bodies and excrement of other cockroaches. They prefer to live in cracks, crevices, and voids away from light (Figure 2). Cockroaches come out looking for food during the dark hours. Within a home, they are mostly found in the kitchen and bathroom, where food and water are available. Areas around the stove and refrigerator in a kitchen usually have the largest number of cockroaches.

Females live 140–280 days, whereas males live 90–140 days. A female produces 5–8 oothecae with a total of 200–250 eggs. The entire life cycle is completed in about 100 days. Active growing field populations are comprised of 80 percent nymphs and 20 percent adults. The major factor limiting German cockroach survival is cold temperatures. At temperatures below 59°F (15°C), cockroaches can survive but will not continue to develop from nymphs to adults.

Management

Inspection and Monitoring

Monitoring the presence and distribution of cockroaches is the first step of a cockroach management program. The simplest method to monitor cockroaches is to visually inspect the kitchen, bathroom, and other areas where food and water sources are available. A flashlight is necessary to aid the inspection. In apartments, the door moldings, hinges of kitchen cabinets, corners inside cabinets, drawers, and back of the refrigerator are ideal harborages for German cockroaches. When cockroach numbers are low, it is often difficult to find them by visual inspection. A more effective monitoring method is to strategically place sticky traps in areas where cockroaches are likely to be present. The traps can be placed inside kitchen cabinets, particularly cabinets beneath the sink and next to the stove; on the kitchen floor near the refrigerator and stove; beside garbage cans; and behind the toilet (Figure 3). If pets or young children are present, place traps in unreachable locations to avoid them accidentally having the sticky trap stick to them. Inspect the traps periodically to determine how large the cockroach infestation is and where they are located. Placing a small piece of bread dampened with beer in the center of the trap will significantly increase the effectiveness of the trap and may even help eliminate cockroaches when very few cockroaches are present.

Sanitation and Non-Chemical Control

Cockroach abundance is associated with sanitation conditions of the environment. Clutter provides hiding places for cockroaches. Keeping the kitchen and bathroom clean and eliminating food, water sources, and clutter will help keep cockroach numbers low. Trash and recycling should be removed daily. In infested homes, pet food should be sealed or removed during the night. Periodically cleaning the floor, inside the cabinets, behind and under appliances and furniture to remove food debris will aid in cockroach elimination. Use a vacuum cleaner with HEPA filter to remove live and dead cockroaches, the fecal materials, shed skins. Sealing cracks and crevices along countertops, baseboards, and around plumbing chases, will reduce harborages.

Chemical Control

There are many cockroach control products available. They are formulated as bait, spray, powder, or total release fogger. Whenever applying any pesticide be sure to carefully read and follow the label use directions for the product being used. Not all of the products are effective. The most effective formula is bait. The bait can be gel bait in syringes or bait stations (Figure 4). Gel bait is usually more effective than bait stations because gel bait can be applied closer to the cockroach harborages and is more palatable. Some of the common active ingredients used in baits are fipronil, abamectin, indoxacarb, hydramethylnon, and dinotefuran.

Thoroughness is the key to achieve good results. Bait is applied as numerous pea-sized small dots at cockroach hiding places such as the underside of the kitchen sink, corners of cabinets, and cabinet door hinges (Figure 5). Larger placement is needed for areas with heavy infestations. After initial application, follow-up treatments should be made in areas where cockroaches continue to persist, based on inspection and sticky trap results. Follow-up treatments should be repeated every 2–4 weeks until cockroaches are eliminated (no cockroaches found over a 4-week period). The amount of bait and distribution of the bait should be based on inspection results. As a general rule, a typical one-bedroom apartment may need 10–30 grams of bait (30 grams per tube) to eliminate the cockroaches.

Among insecticide dusts, boric acid dust has long been used for cockroach management and is still effective for cockroach control, but its effect is slower than bait. Boric acid dust is best used in combination with bait to eliminate an infestation. Boric acid is a very affordable inorganic material and is less toxic to mammals than most synthetic insecticides. It kills cockroaches after they ingest the boric acid as they clean their antennae or legs. When using boric acid dust to treat cockroaches, it is important to apply the dust thoroughly in areas that are not accessible to children or pets, such as under and behind appliances, in cracks and crevices on the wall, or behind wall cabinets. Boric acid will not degrade in the environment but will slowly lose its efficacy after exposure to environmental moisture over time. Re-application after 1–2 months may be necessary if cockroaches continue to be present. Diatomaceous earth dust is another inorganic insecticide. It kills insects by destroying the wax layer on their skin but is less effective than boric acid for controlling cockroaches. Insecticide dusts containing pyrethroids as active ingredients are also available but are rarely used due to much safer and more effective bait products that are available.

Insect growth regulators (IGRs) do not kill cockroaches but will cause cockroaches to stop reproducing. As a result, they are only useful for facilities with chronic and high numbers of cockroaches. IGRs alone cannot provide fast reduction of cockroach numbers and need to be combined with other faster-acting insecticides for long-term control. They are most effective when used in combination with baits.

Liquid insecticides in the form of ready-to-use sprays or aerosols labeled for cockroaches are very common in retail stores and are widely used by consumers. While they are very affordable and easy to use, they are not as effective as bait due to insecticide resistance and/or repellency. Most of the active ingredients in these products belong to an insecticide class called pyrethroids. Examples are permethrin, cypermethrin, deltamethrin, and lamda-cyhalothrin. A thorough application is necessary to achieve good results. Before using a liquid or aerosol spray to control cockroaches, thorough preparations are necessary to avoid contamination of food and cooking utensils. Following application, additional measures are often required to clean pesticide residues from countertops and other surfaces where contact with food is likely. When using these materials, it is best to treat into the cracks and crevices where cockroaches are hiding, such as inside, behind, above, and underneath cabinets. Appliances should be pulled away from the wall to allow for spray application behind the appliances where cockroaches are more likely to be prevalent. Pyrethroid insecticides are repellent to cockroaches and therefore, some cockroaches may appear on walls or floors soon after application. The spray treatment may also push cockroaches to neighboring units through pipe penetrations and common walls. Essential oil-based sprays, often marketed as “all natural” are typically only effective when applied directly on the insect and offer little to no residual effect making them less effective for cockroach control.

Products that are very popular in the marketplace that are not recommended include total release foggers and electronic devices for repelling pests. Both types of products are widely used by consumers but neither are effective for the control of cockroaches. Total release aerosols not only are ineffective at eliminating cockroach infestations, but also can present a fire hazard in homes with gas appliances when excessive numbers of foggers are used. No scientific evidence exists to support the claims made by manufactures of electronic devices used for repelling pests.

Integrated Pest Management

Because cockroaches are aesthetically and medically important pests, the goal of cockroach management should be elimination. An integrated pest management (IPM) approach combines several methods together to eliminate cockroach infestations. First, place sticky traps and conduct visual inspection to find where cockroaches are active; Second, keep the environment clean by daily cleaning and removing garbage, removing pet food at night, and minimizing clutter; Third, apply one or a combination of several chemical control methods (using baits as the preferred method); Fourth, conduct follow-up inspections and re-treatments every 2–4 weeks until no cockroaches are visually observed or found in sticky traps for at least one month. To avoid resistance development, it is recommended to use a variety of different products containing active ingredients from different chemical classes. It is important to remember that products with different names may contain the same active ingredient. An integrated pest management approach using bait as the primary chemical method will not only provide faster elimination, but also reduce insecticide usage and leave less insecticide residue in the indoor environment.

Conclusion

One common mistake by do-it-yourselfers is relying on insecticide sprays as the primary method to control cockroaches. Another common mistake is stopping treatment without realizing small numbers of cockroaches are still present. Frequent spray treatment will cause insecticide resistance development, leave large amount of insecticide residues in homes, and pose potential health risks. Most pest control companies offer monthly or quarterly pest control contracts. Professionals have proper training, experience, and access to more products. Homeowners and property managers may seek professional services if they are not comfortable controlling pests themselves.

Selected References

1. Appel AG. 1998. Daily pattern of trap-catch of German cockroaches (Dictyoptera: Blattellidae) in kitchens. Journal of Economic Entomology 91, 1136–1141.
2. Miller DM, Smith EP. 2019. Quantifying the efficacy of an assessment-based pest management (APM) program for German cockroach (L.) (Blattodea: Blattellidae) control in low-income public housing units. Journal of Economic Entomology 113, 375–384.
3. Ross MH, Mullins DE. 1995. Biology. In Understanding and Controlling the German Cockroach. (Eds MK Rust, JM Owens and DA Reierson) pp. 21–47, Oxford University Press, New York.
4. Wang C, Singh N, Cooper R, Scherer C. 2013. Baiting for success. Pest Control Technology 41 (7), 60–64.
5. Wang, C, Bischoff, E, Eiden, AL, Zha, C, Cooper, R, Graber, JM. 2019. Residents attitudes and home sanitation predict presence of German cockroaches (Blattodea: Ectobiidae) in apartments for low income senior residents. Journal of Economic Entomology 112, 284–289.
6. Zha C, Wang C, Brian B, Yang I, Wang D, Eiden A, Cooper R. 2018. Pest prevalence and evaluation of community-wide integrated pest management for reducing cockroach infestations and indoor insecticide residues. Journal of Economic Entomology 111, 795–802.

July 2020