Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, Ohio 43210-1000

German Cockroach

HYG-2099-97

William F. Lyon

Common Name	Scientific Name
German Cockroach	Blattella germanica (Linnaeus)

German cockroaches rank "fourth or fifth" in the total num- ber of household, structural and institutional insect pest inquiries received from Ohio clientele each year. These are the most common roaches found in homes, apartments, restaurants, supermarkets, hospitals, and other buildings where food is stored, prepared, or served. They eat food of all kinds and may hitchhike into the home on egg cartons, soft drink cartons, sacks of potatoes or onions, used furniture, beer cases, etc. These roaches will move from building to building during the warm summer months. They can develop into large populations and live throughout the home, especially in kitchens and bathrooms. Roaches can foul food, damage wallpaper and books, eat glue from furniture, and produce an unpleasant odor. Some homeowners are allergic to roaches, and the pests can contaminate food with certain bacterial diseases that result in food poisoning, dysentery, or diarrhea. Cockroaches can cause childhood asthma.

Identification

Most cockroaches have a flattened, oval shape, spiny legs, and long, filamentous antennae. Immature stages are smaller, have undeveloped wings and resemble the adults. Adult German cockroaches are light tan to medium brown except for the shield behind the head marked with two dark stripes (separated by a lighter stripe), which run lengthwise on the body. Adults are about 1/2 to 5/8-inch long and have wings, but rarely fly. Wings cover the entire abdomen of females and all except the abdominal tip in males. The male is light brown and rather boat-shaped, whereas the female is slightly darker with a broader, rounded posterior. Young roaches (nymphs) are wingless and nearly black with a single light stripe, separating two black bands, running down about halfway of the middle of the back. Egg capsules are light tan and less than 1/4-inch long.

Life Cycle and Habits

German cockroach females, unlike most other roaches, carry the egg capsule protruding from their abdomen until the eggs are ready to hatch. The case is then dropped in a secluded location, with the nymphs emerging within one day. A female may produce four to eight cases during her lifetime, each containing 30 to 48 eggs. Eggs hatch in about one month, and nymphs develop in 1-1/2 to 4 months. Female roaches live about 6-1/2 months and males live slightly less. The German cockroach produces more eggs and has more generations per year (three to four) than other roaches, and only a few individuals are needed to develop into troublesome infestations. This roach is spread by commerce and transportation as well as mass migrations. It is the most prevalent pest in low income apartments in the United States.

During the day, these roaches may be found hiding, clustered behind baseboard molding, in cracks around cabinets, closets or pantries, and in and under stoves, refrigerators and dish washers. If clusters of roaches are seen during the day, the population is large. Both nymphs and adults are very active and capable of running rapidly. German cockroaches have a high need for moisture and usually travel 10 to 12 feet from their harborage for food and water in kitchens, bathrooms, utility rooms, etc., preferring darkness. Without food or water, adults may die in two weeks, but can live a month with only water.

Control Measures

Integrated Pest Management (IPM)

Integrated Pest Management (IPM) is a systems approach that combines preventive techniques, non-chemical pest control methods and the wise use of pesticides with preference for products that are least harmful to human health and the environment. It is not the total elimination of pesticides but an alternate approach to traditional pest control measures. Complete reliance, in the past, on pesticides alone for pest control allowed certain pests to develop resistance, created potential human exposure to harmful chemicals, produced unsound environmental contamination, and created a threat to nontarget species and pesticide waste. IPM consists of routine inspection and monitoring with treatment only when pests are actually present, thus reducing traditional, routine pesticide application treatment (calendar date sprays) whether pests were present or not.

By following a cockroach IPM plan, cockroach activity is monitored using sticky traps or glue boards. These monitoring stations are placed throughout a structure where roaches are likely to be found such as in dark places along cabinets, walls, under appliances, on pipes, etc., in bathrooms and kitchens. Any tight cracks about 3/8 inch or smaller are good cockroach habitats. Monitoring indicates whether roaches are present and if control practices are working. IPM tools include glue boards, baits, vacuum cleaners, caulking, insect growth regulators (IGRs), etc.

Detection

German cockroaches can be detected by examining the premises after dark with a flashlight. During the day, probing hiding places with a wire or thin wood strip will expose roaches. Adults and nymphs usually hide clustered together. Household sprays of pyrethrins applied to hiding places will flush out roaches, sometimes killing them if they contact the spray.

Prevention and Sanitation

German roaches can move from one building to the next during the summer, entering through cracks in foundations, around loose-fitting doors or windows, and along water and gas pipes. Repair leaky water faucets and pipes. Seal openings such as cracks in foundation walls, exterior walls around air conditioners, doors, windows, floors, ceilings, around plumbing fixtures, electrical outlets, baseboards, etc. with putty, plastic wood or other caulking material. Inspect for roaches and their egg cases in sacks, cartons, boxes, used appliances and furniture, etc., brought into the home. Sanitation is critical in roach control. (Unclean living conditions from housekeeping neglect is the major contributing factor of roach outbreaks.) Clean areas beneath cabinets, sinks, stoves, refrigerators, etc. as well as cupboards, pantry shelves and food storage bins. Clean up spilled foods and liquids. Avoid leaving scraps of food on unwashed dishes and countertops overnight. Keep food in tightly sealed containers, rinse cans and bottles before putting in the trash, and transfer garbage outdoors into roach-proof receptacles away from the house. Leftover pet food should not remain in the feeding dish overnight.

Resistance

To date, only the German cockroach has developed a degree of resistance that presents control problems. There is a natural evolutionary process accelerated by intense selection pressure created through the use of insecticides. (The more insecticide applied, the greater the selection for resistance.) Never increase dosages. For example, by killing off susceptible cockroaches, there remains an untouched resistant roach that becomes a larger segment of the remaining population. As a result, insecticides that at one time controlled a largely susceptible population are no longer effective against the remaining altered population and most of its descendants. (Resistance is passed from parent to offspring as an inherited trait and not acquired during the cockroach's life.)

Some German cockroaches in apartment buildings have been found resistant to certain carbamate, organophosphate, chlorinated hydrocarbon and pyrethroid insecticides. These roaches have shown high resistance to malathion, Ficam & Baygon and lower resistance to diazinon, Dursban & Orthene. For difficult to control populations, use unrelated insecticides (different chemical classes) in a sequential treatment pattern. (Use in a rotation, one after another, over a short period of time.) For example, in the first month use an organophosphate, the second month use a carbamate, the third month use silica gel, the fourth month boric acid and the fifth month resmethrin. By using insecticides that attack the insect at different points in its body, the insect's defense system is overwhelmed. However, some carbamates and organophosphates have similar action sites where "cross-resistance" may occur. For example, selection with Baygon induces the same resistance spectrum as diazinon.

Insecticides

Apply chemicals at roach hiding places. Enter a dark room quietly, turn on the light, and watch where the roaches run. Spot treat these hiding places and known pathways, especially under and behind loose baseboards or molding strips and around pipes or conduits along the walls and through them. Do not treat entire floors, walls or ceilings. Roaches may hide around the kitchen sink or drain board, in cracks underneath cupboards and cabinets, inside the motor compartment of mechanical refrigerators, behind window and door frames, in radio and TV cabinets, and around closet and bookcase shelves. Surfaces where food is prepared should not be treated. Roaches in buildings with multiple dwellings usually require the treatment of other units as well.

There are numerous cockroach insecticide formulations. Some are labeled "general use" for homeowner application, and others are labeled "restricted use" for professional pest control or licensed, certified pesticide applicators only. Before using any insecticide, read the label and follow directions and safety precautions.

Dusts such as bendiocarb (Ficam D), boric acid powder, pyrethrins (Drione) or silica aerogel (Dri-Die) can be applied with a puff duster into hiding places normally hard to reach with a spray.

Sprays, either oil-based or water emulsion, are applied as spot or crack and crevice treatments. These include propoxur, acephate, chlorpyrifos, diazinon, permethrin or resmethrin. Only the licensed certified pest control applicator may apply bendioarb, propetamphos, trichlorfon, cyfluthrin, cypermethrin, deltamethrin, esfenvalerate, lambda-cyhalothrin, tralomethrin and bifenthrin. Insect growth regulators or IGRs include hydroprene (Gentrol) and pyriproxyfen (Archer, Nylar) which act on immature growth stages by contact or ingestion, disrupting molting and development to fertile adults. (A combination of an IGR followed up by use of a bait is often effective.) Some still use contact insecticides in mist or ULV (ultra-low volume) machines to treat the entire indoor area. Open all drawers and closet doors so roach hiding places can best be treated. However, the trend is toward less sprays and aerosols and more IGRs and baits.

Baits

Certain segments of the public such as schools, hospitals, and office buildings may prefer baits to sprays. Baits include pastes, gels, particle baits and bait stations.

Bait advantages: low hazard (toxicity) to people; suited for sensitive accounts; IPM oriented; offer effective control. Disadvantages: high bait cost; precise placement required; not cost effective in heavy roach infestations.

Sticky traps have openings at both ends with the inside surface covered with a very sticky adhesive and slow-release food attractant. Properly placed traps, to and from roach hiding and feeding areas, can catch numerous adults and nymphs daily, especially brownbanded and German cockroaches. Traps are best used along with preventive and insecticidal applications to monitor populations. Trapping can determine harborage areas and infestation severity, monitor effectiveness of pesticide applications, and detect any roach population increases which may require additional pesticide treatments.

Fumigation is seldom used but will clean out a cockroach infestation. It must be applied only by a licensed, certified pesticide applicator.

If a severe cockroach infestation develops or if you are in doubt as to the control measures to use, contact a reputable, licensed pest control firm who has the chemicals, training and experience to do a thorough job.

This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.