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Mohamed Sadiq Shaik, Ashbrook, Aaron, Carlton, Christopher E.
The German cockroach is an important cosmopolitan urban pest found in households, restaurants, food processing facilities, transportation and livestock facilities. Adult German cockroaches are 13-16 mm in length and light to dark brown in color. Adults possess two dark brown to black horizontal stripes on the thorax immediately behind the head. Nymphs possess black stripes down the entire body, do not possess wings and are smaller. Adult males are slender, with tapering abdomens and the end of the abdomen usually exposed behind the wings. Females are stout, with rounded posterior abdomens that are entirely covered by the wings. Female cockroaches carry their eggs in a brown-colored egg case (ootheca or plural, oothecae) that measures 6 to 8 mm in length that extends beyond the abdomen.
German cockroach is one of two species of the genus Blatella occurring in Louisiana. The Asian cockroach, B. asahinai, is similar in overall appearance but the wings are longer, and adults are capable of sustained flight. Asian cockroaches are not considered serious urban pests. German cockroaches are poor flyers and are more likely to be encountered indoors. A third species, Blatella vaga, is common in the western U.S., and is likewise similar in appearance. It is currently not recorded in Louisiana. It could potentially become established, but, like the Asian cockroach, is not considered a pest of concern. Positive species identification of dead specimens requires dissection and should be performed by a qualified diagnostician or taxonomist.
The life spans of male and female cockroaches differ; females have longer life spans, as long as 280 days, whereas males may live up to 140 days. The entire life cycle of the German cockroach completes in 100 days and involves three life stages: egg, nymph, and adult. Oothecae are attached to the female abdomen. Females can produce five to eight oothecae in a lifetime, each containing 25-43 eggs, and 20-30 days are required from oothecal production to nymphal hatch. The formation of a dark greenish-blue line on the ootheca indicates that nymphs will hatch within seven days. The ootheca detaches from the abdomen two days prior to nymphal hatch. Nymphs emerge from the ootheca by breaking the case and undergo six growth stages (instars) prior to molting into adults. Cool temperatures prolong development.
German cockroaches are often associated with poor sanitation. The species is more than a nuisance; it is also a mechanical vector of enteric pathogens and produces asthma-induced allergens, causing serious health issues. Allergen production is the primary health risk posed by German cockroach infestations. Inhalation of these accumulated allergens, such as particles of molted exoskeletons (exuviae) and feces (frass), can cause serious health issues, including allergic reactions, dermatitis, eczema and asthma. Young children and elderly people are more prone to these allergies, as they are more sensitive to bronchial irritants.
German cockroaches move indiscriminately between food areas and areas of poor sanitation, resulting in passive accumulations of various microorganisms (mechanical vectoring) including bacteria, viruses, protists and parasitic worms. Known mechanically vectored pathogens include Streptococcus spp., Escherichia coli, Salmonella typhimurium, Entamoeba histolytica and Trichuris trichiura. These organisms can cause a variety of foodborne diseases. German cockroach feces and salivary secretions contaminate food and food products and produce a foul odor indicative of large infestations. Large German cockroach infestations may result in bites to humans and lead to psychological stress and social stigma.
German cockroaches are nocturnal, engaging in food scavenging and mating behaviors during darkness then hiding in crevices, garbage receptacles, kitchen cabinets and under sinks during the day. These hiding spaces accumulate aggregation pheromones and cuticular hydrocarbons and are filled with exuviae and frass. German cockroaches are omnivorous and feed on a wide range of human foods, including bread, meat, fruits, leather, pet food and even soap. They detect volatile compounds from food sources via olfactory organs. German cockroaches are well adapted to live in close association with humans and have high reproductive rates. Thus, populations can reach very high densities if not managed. They also develop insecticide resistance quickly, making the species difficult to control or eradicate.
By contrast, the related Asian cockroach (B. asahinai) is not considered a pest and does not occur indoors, although it can be abundant in suitable outdoor habitats. Some studies even suggest that it functions as an important natural control agent in soybeans as an egg predator of lepidopteran crop pests.
Sanitation. German cockroaches thrive in environments that provide warmth, humidity and easy access to food and water. Establishing and maintaining proper sanitation is a necessary first step in controlling German cockroach infestations. Key elements of sanitation include eliminating food sources, removing garbage, vacuuming, mopping, washing dishes promptly and storing food in airtight containers. Minimizing water sources by fixing leaky pipes or faucets is also important. Preventing movement of cockroaches between apartments by sealing cracks and crevices in wall spaces and behind cabinets limits spread. Removing clutter such as carboard boxes, grocery bags and stacked paper helps eliminate potential hiding places.
Monitoring. Monitoring is key to identifying the extent and severity of German cockroach infestations. Visual inspections should be conducted in food preparation and dining areas and bathrooms using a flashlight. Cabinets, backs of refrigerators and food storage areas should be checked. Sticky traps can be used to assess populations of insects before, during and after treatment but should only be used indoors to prevent nontarget organisms such as small vertebrates from being trapped.
Chemical control: Baits. Baits are the most effective tools for German cockroach chemical control. Insecticidal baits have been available since the 1980s and have largely replaced spray insecticides. Baits are safe, easy to use and effective when properly applied. Baits are target-specific; thus, reduce risk to nontarget organisms. They typically include attractants and slow-acting insecticides in the formulation. Formulations include gels, pastes, dry flowable baits and bait stations. Over-the-counter baits are also widely available. Placing baits in areas where cockroaches hide or where they frequent during nighttime foraging is most effective. Small quantities in many localities are more effective than large amounts in a few places. Other types of chemical control methods should not be used in the presence of baits.
In addition to direct mortality, baits leverage secondary and tertiary kills. German cockroaches engage in coprophagy (feeding on feces) and cannibalism (feeding on dead cockroaches or body parts), which allows transfer from exposed cockroaches to unexposed cockroaches. This secondary mortality typically occurs in nymphal cockroaches because they do not forage long distances and partly depend on adult feces for nutrition.
Chemical control: Dusts. Inorganic dusts such as silica, diatomaceous earth and boric acid are commonly used for the control of crawling urban pests like cockroaches, bed bugs and ants. Dusts are relatively safe compared to conventional insecticides and are generally nontoxic to aquatic organisms, mammals and other wildlife. Dusts offer various advantages, particularly in their adherence to porous materials like paper and unpainted wood. For German cockroach infestations, dusts are best applied in dry areas because they lose efficacy in high humidity or wet conditions. Dusts should be applied in fine layers because over application can cause cockroaches to avoid treated areas.
Chemical control: Aerosols. Liquid aerosols are extensively used for German cockroach infestations and remain dependable and cost-effective methods for control. During the last few decades, the primary strategy for cockroach control in public housing has been the application of aerosol insecticides, used both preventatively and remedially on a regular schedule, typically monthly. Aerosols provide a quick cockroach suppression, but do not provide a long-term solution. In some cases, they may increase the problem by repelling cockroaches, causing them to move to new areas in the structure. Insecticidal resistance and avoidance of pyrethroids are common problems. Recent studies have shown that total release foggers, commonly referred as “bug bombs,” are ineffective. Additionally, these products carry significant risks such as flammability and exposure to chemicals. If aerosols are used, they should be directly used in areas like cracks and crevices, ensuring that the insecticide is limited to hiding areas and minimizing the potential risk of exposure to people and pets.
Implementing an integrated pest management (IPM) program that combines multiple chemical and nonchemical control techniques can eliminate German cockroach infestations. A well-designed IPM approach emphasizes preventative measures such as sanitation, the strategic use of baits or sprays, vacuuming, trapping and application of insecticidal dusts to not only control existing cockroach populations but also provides a sustainable and long-term solution to prevent future infestations.
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9/3/2025
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Sexual dimorphism and life stages of Blattella germanica (Aaron R. Ashbrook, LSU AgCenter).
Adult German cockroaches on food (Daniel R. Suiter, University of Georgia, Bugwood.org).
Multiple life stages of German cockroaches (Daniel R. Suiter, University of Georgia, Bugwood.org).
