[Cockroach Control Issue] Cockroach Biology Guide

Cockroaches have inhabited the earth for hundreds of millions of years. While there are thousands of cockroach species in the world, only a few are considered pests. The two primary pest species are German (Blattella germanica) and American (Periplaneta americana) cockroaches.

The behavior, biology and ecology of each cockroach species present unique challenges for pest management professionals. Highly adaptive and capable of reproducing quickly, cockroaches have survived intensive eradication efforts. Effective cockroach control can, however, be achieved through a combination of knowledge of the pests and a variety of control methods now available.

GERMAN COCKROACHES. Following is an update regarding German cockroaches:

Biology. German cockroach nymphs fit on the head of a pin and adults are only about 5/8 inch in length. Nymphs are black with a pale yellow band running along their dorsum (back). Adults are brown, with two dark lines running vertically along their pronotum, the “shield” that covers their head.

Because of their small size, German cockroaches are able to harbor in a multitude of areas within a structure. They are primarily found in kitchens and bathrooms, but they may also inhabit walls, ceilings or any hollow area that provides protection.

Behavior. Pest control efforts are hampered by their behavioral characteristics. Unlike other species, gravid (pregnant) females do not deposit their oothecae (egg cases). Rather, the female protects her young by holding onto the ootheca. After hatching, the young tend to stay within the harborage area and consume fecal material as a chief food source. Thus, gravid females and nymphs may be difficult to control with insecticidal baits or liquid treatments that do not reach harborage areas (Kopanic and Schal 1999).

Because of their high reproductive potential, German cockroaches can become resistant to insecticidal treatments. In a structure with millions of cockroaches, resistance by less than one percent of the population can result in a resurgence of an infestation. In fact, a single gravid female left after an insecticide treatment can produce hundreds of offspring. 

AMERICAN COCKROACHES. Following is an update regarding American cockroaches:

Biology. American cockroach adults can reach about 1½ inches in length, however they can still fit through small openings. American cockroaches are chocolate brown in color with two dark spots on their pronotum surrounded by tan or yellow rings. Adults have functional wings and are also adept runners, even with their heads removed. American cockroaches generally are found in restaurants, food processing facilities, human residences, sewers and basements.

Behavior. American cockroach females produce oothecae which they carry for approximately two days before depositing in a protected location. The female will bury her ootheca in sand or soil, or place it on a substrate surface such as wood or cardboard. If the substrate is soft enough, the female will chew a space for the ootheca, deposit it and then cover it with the substrate material using her saliva as glue, making oothecae difficult to locate. Females can produce up to two oothecae per week, depending on their health and environmental conditions. With the average ootheca containing 12 nymphs, the female potentially can produce hundreds of offspring in her lifetime.

CONCLUSION. Both German and American cockroaches will eat about anything and even resort to cannibalism. Therefore, when baiting, a variety of substances may serve as competing food sources. Understanding the pests’ biology and behavior should enable professionals to customize effective treatment programs.   

The author is a technical representative for Syngenta Professional Products. She holds master’s and doctorate degrees in urban entomology from the University of Florida. She can be reached at dbranscome@giemedia.com.

Selected References

Bell, W.J., and K.G. Adiyodi. 1981. The American cockroach. Chapman and Hall, Ltd., New York.

Cornwell, P.B. 1968. The cockroach, Volume 1, A Laboratory Insect and an Industrial Pest. The Rentokil Library, London.

Guthrie, D.M. and A.R. Tindall. 1968. The Biology of the Cockroach. William Clowes and Sons, Ltd., London.

Kopanic, R. J., and C. Schal. 1999. Coprophagy facilitates transmission of bait among cockroaches (Dictyoptera: Blattellidae). Environ. Entomol. 28: 431-438.