Plant & Pest Diagnostics

German Cockroach (Blattella germanica)

Introduction

The German cockroach is by far the most important and usually the most common of the cockroaches. In addition to being a nuisance, it has been implicated in outbreaks of illness, the transmission of a variety of pathogenic organisms including at least one parasitic protozoan, and allergic reactions in many people. This species has worldwide distribution.

Recognition

Adults about 1/2-5/8″ (13-16 mm) long. Color light brown to tan except for 2 dark, almost parallel longitudinal stripes/bars/streaks on pronotal shield. Female darker than male, her abdomen broader. Rarely glide or “fly”.

Nymphal instars 1-2 with thorax dark brown to black but having pale lateral margins, meso- and metathorax pale/white centrally but with a continuous dark stripe near each margin; thorax and abdomen light brown ventrally. Later instars (3rd on) with 2 dark longitudinal stripes on pronotum continuous with dark abdomen, and abdominal segments usually with central areas pale on dorsum.

Ootheca or egg capsule yellowish brown but usually two-toned, paler end attached to female; about 1/4-3/8″ (6-9 mm) long, with length more than twice width; subdivisional furrows extending entire width; slightly bowed or arched; and with about 15-20 (range 925) eggs on each side.

Similar groups

(Adults only). (1) Asian cockroach (Blattella asahinai) with almost identical color pattern, attracted to lights, flies readily, breeds outdoors in leaf litter, presently known only from Florida, identification should be confirmed by an expert. (2) Brownbanded cockroach (Supella longipalpa) and Pennsylvania wood cockroach (Parcoblatta pensylvanica) lack 2 dark longitudinal stripes on pronotal shield. (3) Field cockroach (B. vaga) with a median dark line between eyes on front of head. (4) Other cockroaches are either smaller or larger, lack characteristic pronotal stripes, and/or are not associated with structures.

Biology

The female carries her ootheca until it is within 1-2 days of hatching, and then deposits it in a sheltered area/site. On the average, the female will produce about 5 oothecae (range 4-8), averaging 30-40 eggs (range 18-50) each.

Developmental time (egg to adult) usually varies from 54-215 days, averaging about 103 days; under lab conditions of 80 degrees F/27 degrees C and 40% relative humidity, usually only 50-60 days are required. This means usually 3 to 4 generations per year, but up to 6. Adults live about 100-200 days (range 1-303). Established/mature German cockroach populations are typically composed of at least 75% nymphs.

Habits

German cockroaches are found throughout structures but show a preference for warm (70 degrees F/21 degrees C) and humid places. They are usually found in kitchens and secondarily in bathrooms, but infestations often occur in rooms where people eat and drink while watching television such as the den, bedroom, etc. Any crack or crevice located near a source of food and/or water is prime harborage, and they spend about 75% of their time in such harborages. First instar nymphs require a crack of about 1/32″ (1 mm) whereas, adults require a crack of about 3/16″ (5 mm) in width.

These cockroaches are most commonly introduced into buildings via paper products or paper packaging such as grocery bags, cardboard boxes, drink cartons, and via secondhand appliances such as refrigerators, televisions, VCR’s, microwaves, etc. They have been observed to migrate from building to building on warm evenings, but this rarely occurs. Although uncommon, they can survive outdoors during the warm months.

They feed on almost anything with nutritive value including all kinds of food, and such things as soap, glue, and toothpaste.

Activity periods vary with life stage, age, and physiological state. For instance, reproducing females are quite active whereas, gravid (with ootheca) females are relatively inactive starting about the 5th day after mating and go only to food and water when necessary. Males spend most of their time in harborage, even at night. All nymphs become immobile and stay in harborage during the last 3 days of each instar while they prepare to molt. Hence, about 1/3 of the time the cockroach nymphs will not be found or found exposed during an inspection.

Control

Controlling cockroaches is very difficult, especially in situations where there are large numbers of roaches present. Along with insecticides, effective control requires improved sanitation and waste can management, and persistence. Serious thought should be given to hiring a respectable pest control company. Baits are particularly effective, but correct placement along junctions and/or in cracks and crevices in or near harborages is essential. Incorporating IGRs (insect growth regulators) into the service helps with long-term control. Be sure to follow label directions.

A number of good insecticides and bait systems can be obtained on the web. One such site that offers products for do-it-yourselfers is:

http://www.doyourownpestcontrol.com/german.htm#control

Be sure to read and follow all instructions and safety precautions found on the label before using any pesticide.