The Purdue Plant and Pest Diagnostic Laboratory

P&PDL Picture of the Week for
January 14, 2008

German cockroach photos are rare

Timothy J. Gibb, Insect Diagnostician, Department of Entomology, Purdue University

A cockroach is not very photogenic, at least I rarely have photos sent to me here in the pest diagnostic laboratory. I can think of several reasons why a roach may not be photographed very often. ‘Flat out ugly’ is probably the biggest single reason but the unpleasant life cycle and living conditions where they thrive is also reason for lack of photos. They require only food, water and a warm place to harbor in between feeding events. They are able to eat whatever food becomes available to them, commonly foraging not only on stored foods, pet foods and table scraps that may be lying around but also in uncleaned dishes or garbage receptacles. They usually only come out at night when no one else is around but their presence can easily confirmed by the mess that they leave after feeding and harboring in an area. Signs are unmistakable and they emit a unique smell if they have been around a while. So again, with such a disgusting life style who would possibly want a photo, especially of one feeding in your own kitchen. The fact is that most people typically go to excessive lengths to eradicate them from their homes.

The German cockroach one of several species that can be found inside homes but it is the species that gives all other cockroaches a bad name. It occurs throughout the world primarily in association with humans and often plagues multifamily dwellings in the United States. Because it does not directly harm people it is considered an aesthetic pest, and the action threshold for this insect depends upon the tolerance of the people living in the infested dwelling. That is why infestations in multifamily dwellings are so common. The building is subject to the lowest common tolerance level. If one apartment remains home to a large infestation, the entire building remains infested regardless of control efforts in other areas.

The German cockroach has three life stages typical of insects with incomplete metamorphosis: the egg, nymph, and adult.  Adult German cockroaches are generally about 5/8 inches in length, are light brown except for the shield behind the head that is marked with two dark stripes running lengthwise to the body.  They have long antennae and can run in short bursts very quickly.  Eggs are enclosed in capsules that are light tan and usually yield about 36 young.  Young roaches are wingless and nearly black with a single light stripe running down the middle of the back.

The entire life cycle is completed in about 100 days and under ideal conditions, population growth has been shown to be exponential.

Many classes of insecticides including organophosphates, carbamates, pyrethroids, amidinohydrazones, insect growth regulators, inorganics, microbial, and botanicals are available for controlling German cockroaches. These are available in a wide variety of formulations including baits, sprays (emulsifiable concentrates, wettable powders, microencapsulated), dusts, and powders.   Baits and baiting technology have recently been improved such that roach infestations have been eliminated rather than just reduced in many buildings. Non toxic and low toxic alternatives for German cockroach control are available. Sticky traps can be used to monitor or reduce population size.

Improving sanitation by eliminating food and water sources and clutter can have a significant impact on reducing populations. Exclusion practices such as sealing cracks and crevices will reduce harborage space and thus infestations.

Often a combination of the above tactics are required to effectively manage an existing roach infestation.  After the roaches are eliminated, sanitation and exclusion techniques usually are sufficient to keep them at bay.

Click image to enlarge

german cockroach

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service