The German cockroach has always ranked among the Top 10 structural pests worldwide, despite the advent of professional pest management products and trends over the decades. Its common name is misleading, by the way — experts agree this pest probably originated from Asia, not Europe.
Adult German cockroaches measure 1/2- to 5/8-inch long and are light brown to tan, except for two dark, parallel stripes on their pronotal shields, which partially cover their heads. Females have broader abdomens than males. These cockroaches are not good fliers; they use their wings like parachutes to break their falls.
Nymphs have two dark brown to black stripes on their tan thoraxes, similar to adults, and have dark abdomens. The tan-colored egg capsules measure 1/4- to 3/8-inch long, are about three times longer than wide, have subdivisional furrows across their widths, are slightly arched, and contain 30 to 48 eggs.
German cockroaches are spread from structure to structure mainly by hitchhiking in boxed or bagged produce, packaged food, clothing, furniture and appliances. They carry a number of microbial pathogens on their tarsi and can contaminate whatever they touch, including food, dishes and utensils. Children often suffer asthmatic reactions from respiratory exposure to the protein allergens in airborne fragments of cockroach exoskeleton and feces, especially where chronic infestations occur in low-income public housing.
BIOLOGY
The German cockroach has three developmental stages (incomplete metamorphosis): egg, nymph and adult. Females carry egg capsules extruded from their abdomens until they are within one to two days of hatching, and then deposit them in sheltered areas. At room temperature, one capsule is produced about every six weeks. On average, a female will produce about five egg capsules (range four to eight) during her lifetime. Developmental time (from egg, to six to seven nymphal instars, to adult) usually varies from 45 to 215 days, depending on temperature and availability of food and water. In warm, humid kitchens and apartments, however, only 45 to 60 days are required. This means usually three to four generations per year, but up to six. Adults live about 100 to 200 days. Established German cockroach populations typically are composed of at least 75 percent nymphs.
IPM MEASURES
When inspecting and treating for German cockroaches, don’t overlook potential harborages, enlist customer cooperation with sanitation and food storage, and:
- Use pest vacuum cleaners to remove as many cockroaches from accessible harborages as possible.
- Use sticky monitors with food or pheromone lures to help reduce infestations, determine locations and levels of infestations, and evaluate efficacy of the treatments.
- Place insecticides where cockroaches inhabit cracks, crevices and warm, dark cavities in appliances, furniture and structural voids near food and moisture.
- Consider using non-repellent residual liquid and dust insecticide formulations, as well as containerized insecticide baits in sensitive situations.
- Consider alternating baits in structures where an ongoing treatment program is in place. Be alert to the possibility of bait rejection by some cockroach populations.
- Do not use total-release aerosol insecticides. Most urban populations are somewhat resistant to pyrethroids, and they likely will not deliver lethal doses of active ingredients to deep harborages and alarmed cockroaches can temporarily close their spiracles and escape to deeper harborages.
You can reach Wegner, technical director and staff entomologist of Varment Guard Environmental Services in Columbus, Ohio, at 614-794-8169 or e-mail gerry.wegner@varmentguard.com.
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