How to Manage Pests
Pests of Homes, Structures, People, and Pets
Cockroaches, or “roaches”, are among the most important household pests. Indoor cockroaches are known as significant pests of public health, and outdoor species that find their way inside are considered serious nuisance pests as well as potential public health pests. Cockroaches range in size from less than 1/2 inch long to almost 2 inches long and are mostly nocturnal insects that feed on a wide range of organic matter. Most cockroaches harbor within moist, dark crevices when not foraging for food. They crawl quickly and may climb rough surfaces. A few species can fly short distances or glide as adults during warm nights, but most have no wings, reduced wings, or otherwise do not fly.
People are repulsed when they find cockroaches in their homes and other buildings. Indoor infestations of cockroaches are also important sources of allergens and have been identified as risk factors for development of asthma in children, especially within multi-unit housing environments. The levels of allergens present have been directly correlated to both cockroach density and the conditions that contribute to heavy infestations, such as housing disrepair and poor sanitary conditions.
There are five species of cockroaches in California that are commonly regarded as pests: German cockroach, brownbanded cockroach, oriental cockroach, American cockroach, and Turkestan cockroach.
IDENTIFICATION AND LIFE CYCLE
Cockroaches are medium-sized to large insects in the order Blattodea (superorder Dictyoptera). They are broad, flattened insects with long antennae and a prominent, shield-shaped section behind the head called the pronotum. Termites also belong to the Dictyoptera and are closely related to cockroaches.
Some people confuse cockroaches with beetles, but adult cockroaches have membranous wings and lack the thick, hardened forewings of beetles.
Almost all cockroaches are nocturnal. They have a tendency to scatter when disturbed. Young or immature cockroaches, called nymphs, undergo gradual metamorphosis as they develop and grow into adults, which means they resemble adults and have similar feeding habits, but they do not have fully developed wings and are not reproductively active. Immediately after molting, cockroaches are white, but their outer covering darkens as it hardens, usually within hours. Nymphs are typically the most abundant stage of cockroach found in field populations.
An adult female cockroach produces an egg case, called an ootheca, which it carries around protruding from the tip of the abdomen. The adult female German and field cockroaches carry their egg cases for most of the 30-day incubation period and then drop it about the time the eggs hatch. The other species covered here carry it for only a short time before depositing it in a suitable location where it incubates for weeks or months. In most cases, egg cases are deposited in dark, moist crevices and other protected areas. The time required for a cockroach to complete its life cycle, from egg to reproducing adult, varies by species, from just a few months to more than one year.
Cockroaches hide in dark, warm areas, especially narrow spaces where surfaces touch them on both sides. Adult German cockroaches can hide in a crack 1/16 inch wide. Immature cockroaches tend to stay in even smaller cracks where they are well protected. Cockroaches tend to congregate in corners while foraging and generally travel along the edges of walls or other surfaces.
It is important to correctly identify the species involved in a cockroach infestation so that the most effective control method(s) may be chosen.
COCKROACHES THAT LIVE INDOORS
The German cockroach (see Table 1), Blattella germanica, is the most common indoor species in California (and perhaps worldwide), especially in multi-unit housing environments. They prefer food preparation areas, kitchens, and bathrooms, favoring warm (70° to 75°F), humid areas that are close to food, water, and dark areas for harborage. Severe infestations may spread to other parts of buildings.
Of all the cockroach species in California, the German cockroach is the most persistent and troublesome; it lives and breeds in indoor locations associated with food preparation and may pose health concerns due to contamination of food and production of indoor allergens. German cockroaches may become pests in homes, schools, restaurants, hospitals, warehouses, apartments, and in virtually any structure that has food preparation or storage areas. They contaminate food and eating utensils, destroy fabric and paper products, and impart stains and unpleasant odors to surfaces they contact.
German cockroaches are believed to be capable of transmitting numerous disease-causing organisms such as Staphylococcus spp., Streptococcus spp., hepatitis virus, and coliform bacteria. They have also been implicated in the spread of typhoid and dysentery.
The female carries around a light beige egg case, about 1/4 inch long, until 1 to 2 days before it hatches, when she drops it. Sometimes the egg case hatches while it is still being carried by the female. Each egg case contains about 30 young, and a female may produce a new egg case every few weeks. This species has the fastest reproductive cycle of all the common pest cockroaches: a single female and her offspring can produce over 30,000 individuals in a year.
The brownbanded cockroach (see Table 1), Supella longipalpa, is not as common as the German cockroach in California and accounts for only about 1% of all indoor infestations. This species prefers temperatures of about 80°F, about 5° to 10°F warmer than that preferred by German cockroaches. Favored harborage locations include crevices within or near electrical appliances, behind artwork and decorations on walls, within hollow legs of furniture, and within accumulations of clutter. They are not usually associated with food preparation areas but may be found in offices, animal care facilities, kitchens, schools, laboratories, industrial facilities, and hospitals. Brownbanded cockroaches prefer starchy foods, such as the glue on stamps and envelopes.
Adult males sometimes fly when disturbed, especially at higher temperatures (above 85°F), but females cannot fly. Females glue light brown egg cases, which are about 1/4 inch long, to ceilings, beneath furniture, or in closets or other dark places where eggs incubate for several weeks before hatching. Multiple egg cases may be glued together in large deposits. Each female and her offspring are capable of producing over 600 cockroaches in one year.
COCKROACHES THAT LIVE OUTDOORS
The oriental cockroach (see Table 2), Blatta orientalis, is sometimes referred to as a water bug or black beetle. It lives in cool, dark, damp places like garages, basements, water meter boxes, and drains. It is most likely to occur in single-family dwellings that are surrounded by vegetation such as woodpiles, ivy, and ground cover. It is also common in outside locations where people feed pets, livestock, or wildlife.
Oriental cockroaches prefer cooler temperatures than the other species do, and populations of this species often build to large numbers in masonry enclosures such as water meter boxes. At night, oriental cockroaches may migrate into buildings in search of food, water, or mates. They usually remain on the ground floor of buildings and move more slowly than the other species.
Oriental cockroaches do not fly and are unable to climb smooth vertical surfaces; consequently they may be found trapped in porcelain sinks or tubs after falling in or climbing up through damaged drain pipes.
Females deposit dark red-brown egg cases, which are about 3/8 inch long, in debris or food located in sheltered places. Each female and her offspring can produce nearly 200 cockroaches in one year. Development from a newly emerged nymph to adult can take from 1 to 2 years or more.
The Turkestan cockroach, Blatta lateralis (see Table 2), is a newer invasive species usually found in outdoor locations such as water meter boxes, cracks between blocks of poured concrete, compost piles, leaf litter, potted plants, and sewer systems. This species is often sold online and reared as food for insect-eating pets. Females are often confused with the oriental cockroach but can be distinguished by the cream-colored markings along the edges behind the head and around the short, rounded wings. Males may look similar to the American cockroach but are smaller and have yellowish-beige wings with cream-colored stripes along the edges (see Table 2). The nymphs are dark brown to black with reddish heads, thoraxes, and legs.
The biology of the Turkestan cockroach is similar to that of the oriental cockroach, though Turkestan cockroach females reach maturity faster and produce more eggs during their lifetimes than oriental cockroach females. In recent years, the oriental cockroach is being displaced by the Turkestan cockroach, especially in southern California, the Central Valley, and other warm, dry parts of the state.
The American cockroach (see Table 2), Periplaneta americana, prefers warm and humid environments, usually with temperatures above 82°F. Under the right conditions, they readily live outdoors. Occasionally, they forage from sewers and other areas into the ground floor of buildings, especially if pipes are damaged, screens are missing, or water traps in drains are faulty. They are common in sewers, water meter boxes, storm drains, steam tunnels, animal-rearing facilities, and zoos.
Because American cockroaches may come into contact with human excrement in sewers or with pet droppings outdoors, they are capable of transmiting bacteria that cause food poisoning (Salmonella spp. and Shigella spp.).
Adult females carry the egg cases around for about 6 days and then cement them to a protected surface where they incubate for about 2 months or longer. The egg cases, which are about 3/8 inch long, are brown when laid but turn black in 1 to 2 days. Each egg case contains about 12 young; a female and her offspring can produce over 800 cockroaches in one year.
The field cockroach (see Table 2), Blattella vaga, prefers outdoor locations in leaf litter and plant debris but may invade indoor areas when it is hot or dry outdoors. They are most commonly found in southern California and desert areas. Field cockroaches are often mistaken for German cockroaches.
Adult females carry the egg cases until they are ready to hatch. Each egg case usually contains between 30 and 40 young. Development from a newly emerged nymph to adult can be completed in about 3 months.
The three-lined cockroach (see Table 2), Luridiblatta trivittata, is native to Mediterranean countries such as Algeria, Morocco, Spain, and Libya. Little is known about the biology of this species. In its native range, it is found in leaf litter in semi-arid forests. Within California, it has been observed harboring in irrigated landscapes in leaf litter and plant debris. They are currently found in the San Francisco Bay Area as well as other parts of northern and central coastal California.
Three-lined cockroaches can sometimes invade structures in late summer and autumn in California, in search of water during the driest parts of the year. Attempts to rear three-lined cockroaches in the laboratory have so far been unsuccessful.
The invasive smokybrown cockroach (see Table 2), Periplaneta fuliginosa, has been considered a nuisance pest in some parts of southern California, but it is now rarely encountered. This species is usually found outside in decorative plantings and planter boxes, woodpiles, garages, and water meter boxes; it may occasionally inhabit municipal sewers. Smokybrown cockroaches prefer the upper parts of buildings; they also may live under shingles or siding and sometimes get into trees, shrubs, and other vegetation during summer months. They sometimes invade homes, taking refuge in areas such as the attic. Adults can fly, especially on warm humid evenings.
Females carry the dark brown to black egg case, which measures about 3/8 inch long, for about 1 day before dropping it. Eggs can quickly hatch in 24 days or take 70 days after being laid, depending on temperature. About 40 to 45 nymphs hatch from a single egg case. Nymphs are dark brown and have white segments at the end of their antennae and across their backs.
The Australian cockroach, Periplaneta australasiae, is a tropical species and prefers warm and humid habitats. It is occasionally encountered in greenhouses and animal rearing facilities, and zoos. The adults resemble American cockroaches but are recognizable by the cream-colored band along the fore wing. The life cycle is similar to that of American cockroaches.
Managing cockroaches is not easy. For serious indoor infestations and other large or complex cockroach problems, professional pest control services are often required. In some cases, however, you can manage cockroaches on your own. To be successful, you must first determine which species is present and where they are located. The more hiding places you locate and manage, the more successful your control program will be. Remember that most cockroaches are tropical and like warm, dark hiding places with access to water. Some of these locations may be difficult to access.
To prevent cockroach infestations, it is essential to reduce food and water sources as well as known and potential hiding places. If cockroaches have access to food, baits (which are primary control tools) may take longer to provide satisfactory control. Insecticide sprays alone will not eliminate cockroaches. An integrated pest management (IPM) approach that uses several control methods is usually required.
Monitoring for Cockroaches
Traps. Sticky traps or glue boards offer the best way to detect and monitor cockroach populations. By placing traps in several locations and inspecting them regularly, you can identify the most severely infested areas and know where to concentrate control efforts. Traps can also be very helpful in evaluating the effectiveness of control programs. Most cockroach sticky traps available at home and garden stores work well for monitoring. These traps are open at both ends and are lined inside with a sticky material.
To be effective, traps must be placed where cockroaches are likely to encounter them when foraging. The best places are at the junctions of floors and walls and close to sites where cockroaches are suspected. Good potential monitoring sites can be determined by accumulations of fecal matter (e.g., dark spots or smears), cast skins, egg cases, and live or dead cockroaches.
Place traps in all corners of the room to give you an idea where cockroaches are entering. In the kitchen, put traps against walls behind large appliances and in cabinets. Number the traps so you can keep records for each trap separately.
Check the traps daily for several days until it is apparent where the greatest number of cockroaches are being caught. Many times, cockroaches will be caught within the first 24 hours of placing a trap. Discard sticky traps by placing them in a sealed plastic bag in the trash.
To evaluate success, keep records of cockroaches trapped in different locations before and after you start your management efforts.
You can also detect a cockroach infestation by using a flashlight to inspect cracks, underneath counters, around water heaters, and in other dark locations. A small mirror on a long handle can be useful in hard-to-see areas.
Sanitation. Cockroaches thrive where food and water are available to them. Even tiny amounts of crumbs or liquids caught between cracks provide a food source. Important sanitation measures include the following:
Exclusion and Removal of Hiding Places. During the day, cockroaches hide around water heaters, in cupboard cracks, stoves, crawl spaces, outdoor vegetation, and many other dark locations. They invade kitchens and other areas at night.
Limiting hiding areas or avenues of access to living areas is an essential part of an effective management strategy. False-bottom cupboards, hollow walls, and similar areas are common cockroach refuges that should be properly sealed.
Limit Access. Prevent access to the inside of buildings through cracks, conduits, under doors, or through other structural flaws. Take the following measures if observation or trapping shows cockroaches are migrating into a building from outdoors or other areas of the building:
Insecticides are most effective in controlling cockroaches when combined with sanitation and exclusion practices that limit the cockroach’s ability to establish or reinvade. Pesticides alone will not solve a cockroach problem.
If insecticides are used, they must always be used with extreme care. Indoor chemical control is warranted only if the cockroach population is established, not for an incidental intruder or two.
Baits. Bait products are the primary pesticides used to treat cockroach infestations. They can be packaged as pastes, gels, and granules (Table 3).
Most insecticides used in baits are slow acting. Baits do not control all cockroaches equally. For instance, brownbanded cockroaches are especially difficult to control using baits. Female cockroaches with egg cases do very little feeding and avoid open spaces, so they are less likely to be immediately affected by a bait. An effective bait program does not give immediate results but instead may take 7 days or longer. Baits can be quite effective for long-term control of cockroaches. Removing other food sources will greatly enhance the effects of baits.
As with sticky traps, insecticidal baits do not attract cockroaches over long distances, so place them near hiding spaces or where roaches are likely to encounter them while foraging.
Outdoors, place baits and bait stations around building perimeters (in valve or water meter boxes, wood piles, and around planters.
Indoors, place baits under appliances, along walls, and in cabinets. Baits can also be placed next to fecal specks and droppings of cockroaches. These deposits contain a natural attractant or aggregation pheromone. Look for these fecal specks and droppings under kitchen counters, behind kitchen drawers, and in the back of cabinets.
Bait Stations. The most popular bait application method for home use is within prefilled bait stations, small plastic units that contain an attractive food base along with an insecticide. Refillable bait stations are available in stores and can be refilled with bait granules or gel.
The advantage of bait stations is that insecticides are confined to small areas within tamper-resistant containers rather than being dispersed widely, potentially reducing exposure to people and pets. Baits in stations remain effective for many months.
Gel Bait. For crack and crevice treatments, gel baits can be very effective. Apply gel using a bait gun or syringe in small dabs in cracks and crevices where cockroaches will find it.
Gel baits are very effective when placed in or near locations where cockroaches harbor or forage. In some cases, gels may need to be reapplied since deposits harden over time. Gels are very effective when applied to manage German cockroaches and other species living inside structures. Research suggests that gel baits, applied within bait stations and in-ground utility ports, can also be used to effectively manage outdoor cockroaches.
Available commercial baits (see Table 3) may contain abamectin, boric acid, fipronil, hydramethylnon, indoxacarb, clothianidin, or imidacloprid mixed with a food base. Some of these products are only available to licensed professionals.
Dusts and powders. Insecticidal dusts (Table 4) can be important parts of an IPM program when applied in enclosed, out-of-the-way locations where cockroaches may hide. The most common active ingredient used against cockroaches is boric acid. Boric acid powder is a contact and oral insecticide and can be used preventively or when treating existing infestations.
Boric acid is not repellent, and if it remains dry and undisturbed, it provides control for a very long time. Because it has a positive electrostatic charge, the dust clings to the body of a cockroach as it walks through a treated area, and the cockroach ingests small amounts when it grooms itself.
Boric acid powder has fairly slow activity, and it may be 7 days or more before it has a significant effect on a cockroach population. Boric acid is not recommended for outdoor use since it is toxic to plants.
Blow dusts and powders into cracks and crevices or lightly spread it in areas where visible residues are not a problem and where people will not come into contact with it. Remove kick panels on refrigerators and stoves and apply a light film of dust throughout the entire void underneath these appliances. Thin films of dust are more effective than thick layers, which may cake and clump together.
Holes the size of the tip of a puff-type applicator can be drilled into the top of kick panels beneath cabinets, and dusts and powders may be applied through the holes to these areas as well as under the sink, in the void space between the sink and wall, and around utility pipe penetrations. Also treat along the back edges and in corners of shelves in cabinets, cupboards, pantries, and closets.
Formulated as insecticides, boric acid products usually contain about 1% of an additive that prevents caking and improves application properties. If a deposit gets wet and then dries and cakes, it loses its electrostatic charge and will not be picked up readily by cockroaches. If this occurs, clean up old deposits and reapply to these areas.
Desiccant dusts such as diatomaceous earth and silica aerogel are repellent and effective when applied to voids and other out-of-the-way places. Silica aerogel readily absorbs waxes from the surface of insects, resulting in their desiccation (dehydration) and death. Silica aerogels may be applied during construction or to prevent cockroaches from becoming established.Foggers, Sprays, and Aerosols. Applications of aerosol insecticides and total-release foggers (‘bug bombs’) are often ineffective since they don’t reach the crevices where cockroaches harbor and breed and can be hazardous due to flammability and exposure concerns.
Although sprays may provide a quick, temporary knockdown of cockroaches, they do not give long-term control. They may also repel and disperse cockroaches to other areas of the building from which they may return later.
Cockroaches have also become resistant to many insecticides in common sprays and aerosols that formerly controlled them. Sprays should not be necessary if an IPM program is followed that uses sanitation, exclusion, and appropriate baits and dusts.
Insecticide treatment of harborage sites for oriental, Turkestan, and American cockroaches may be required when populations of these species are high and cockroaches are moving into buildings.
After a cockroach IPM program has been started, evaluate the effectiveness of the methods that are being used with regular monitoring. Use traps or visual inspections to help determine if further treatment is necessary.
If populations persist, reevaluate the situation. Look for other sources of infestations, make sure that all possible entryways are blocked, be certain that food and water sources are eliminated as much as possible, and continue sealing and eliminating hiding places. It may be necessary to move bait stations to other locations, use more stations, apply more bait, or consider a different bait product.
When cockroach populations are under control, continue monitoring with traps on a regular basis to make sure re-infestation is not taking place. Maintain sanitation and exclusion techniques to avoid encouraging a new infestation. If severe re-infestations continue to recur, consider having the infested areas modified or remodeled to reduce the amount of suitable habitat for cockroaches.
Quarles W. 1998. Pheromones and non-toxic cockroach control. IPM Practitioner, Vol. XX (5/6):1-7.
Rust MK. 2008. Cockroaches. Public Health Significance of Urban Pests (eds.). X Bonnefoy, H Kempen, K Sweeny. WHO Regional Office for Europe, Copenhagen, Denmark.
Rust MK, Owens JM, and Reierson, DA, eds. 1995. Understanding and Controlling the German Cockroach. New York: Oxford University Press.
Pest Notes: Cockroaches
Authors: Andrew M. Sutherland, UC Cooperative Extension, SF Bay Area, and UC Statewide IPM Program; Dong-Hwan Choe, Entomology, UC Riverside; Michael K. Rust, Entomology, UC Riverside.
TECHNICAL EDITOR: K Windbiel-Rojas
ANR ASSOCIATE EDITOR: BJ Aegerter
EDITOR: B Messenger-Sikes
Produced by University of California Statewide IPM Program
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