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- Cockroaches are a common pest, infesting both indoor and outdoor areas.
- Effective control of pest cockroaches involves thorough inspection, reducing sources of food, water and shelter, pesticides or baits, and ongoing maintenance.
- Several species of cockroach are common in Victoria. Species identification will help you decide the best method of inspection and control.
Cockroaches belong to the insect order Blattodea. There are over 4000 species of cockroaches worldwide, only a few of which are considered major pests. The high pest status of cockroaches is largely attributed to their wide distribution, close association with humans and potential to carry disease.
The faeces of some species of cockroach contain a pheromone. These cockroaches press or smear their faeces onto surfaces to mark feeding and aggregation sites.
Conditions that favour cockroach infestations are those that provide abundant food, water and shelter. Cockroaches eat virtually any animal or vegetable material, including paper, fabric, leather, starches and grease particles.
Cockroaches are generally nocturnal. Any active cockroaches observed during the day are often indicative of a large infestation. Cockroaches are gregarious (they congregate together), and frequently groom themselves. This behaviour is exploited by pesticides such as dusts that come in contact with the feet or body of the cockroach and are ingested during grooming.
Cockroach eggs are enclosed in a purse-shaped egg case, which may be carried, dropped or glued to a surface. When hatched, the nymphs congregate with adult cockroaches and mature after a number of moults. The number of nymphal moults, time taken for maturation and the adult lifespan depends on the species of cockroach.
Effective cockroach control relies on the education and co-operation of the residents of the infested area. This requires:
1.A thorough inspection of the infested area.
- A torch or pyrethrin aerosol may be used to flush cockroaches out of their harbourages. Sticky traps can be effective for long-term monitoring of populations.
2.Measures to reduce access to food, water and shelter, including:
- Maintaining a high standard of hygiene
- Reducing water availability by removing unnecessary containers of water and repairing leaky taps and pipes.
- Storing food in sealed airtight containers, emptying garbage bins regularly and keeping garbage bin lids tightly closed.
- Sealing cracks and crevices where possible.
3.Application of pesticides to areas that will target the cockroaches, may consist of any or a combination of:
- Surface sprays applied to cracks, crevices and voids that may harbour cockroaches, and surfaces where cockroaches travel. Food-handling surfaces must not be treated. Cupboards and pantries should be emptied before treatment.
- Space sprays or ULV (ultra-low volume) machines to treat an entire indoor area. It should be noted that space sprays are unlikely to effectively penetrate harbourages and the trend is toward using fewer sprays and more dusts and baits.
- Dusts are used in areas that cannot be treated with wet sprays. Dusts can be applied to cracks and crevices, in electrical equipment, and in wall and roof voids. They should always be applied lightly and carefully to avoid the risk of humans coming in contact with the dust.
- Baits may be in the form of gels, pastes, particles or bait stations. Baits are becoming increasingly useful in cockroach control and the use of baits can offer safety advantages if treatment is required in commercial food-handling areas, schools or hospitals.
Chemicals must always be used according to label directions and the effectiveness of chemical control may be limited by poor hygiene.
4.Follow-up inspection and monitoring.
Major pest species
German cockroach (Blatella germanica)
German cockroaches are amber in colour, 12-15 millimetres long when fully grown, with two dark longitudinal stripes. They have wings that extend beyond the abdomen, but do not appear to fly. They are the most prolific breeder of the pest cockroaches; generally having three to four generations per year, with up to 40 offspring per generation. They take as little as 40 days to develop from hatchling to adult. Adults often carry egg sacs.
German cockroaches will eat almost any organic material, ranging from crumbs to built-up grease. They can survive for up to a month without food, provided that water is available.
German cockroaches congregate in warm, undisturbed areas of high humidity. Most infestations are found in kitchens. Cockroaches may be found under sinks, in and under cupboards and drawers, and around electrical equipment such as refrigerators. They hide in cracks and crevices during the day and feed at night. Sightings in other areas of the house, for example bedrooms, may indicate a large infestation. When inspecting for German cockroaches a torch should be used to search for live or dead cockroaches, faecal pellets (small, dried faecal particles), faecal smears, cast off skins and empty egg cases. A thorough treatment of all cracks and crevices, voids and surfaces on which cockroaches are likely to travel is required in infested areas.
German cockroaches generally spread to new locations as stowaways in cardboard boxes or crates of food and drink. A few individuals can establish themselves in a new location and rapidly breed to huge numbers.
American cockroach (Periplaneta americana)
American cockroaches are the largest common pest species of cockroach, reaching 35-40 millimetres in length. They are reddish-brown in colour with a pale yellow border around the upper part of the thorax and pale legs. They have wings and males can be distinguished from females as their wings extend beyond the tip of the abdomen. American cockroaches are capable of flying short distances in warm conditions.
Females produce up to 50 large egg capsules in their lifetime, each containing 12 to 16 eggs. They usually carry these around for about 2 days, then drop them or glue them to surfaces close to food and water. Nymphal development takes 6-12 months and the adult lifespan is 6-12 months.
American cockroaches prefer to feed on decaying organic matter, but will eat most other organic foods, including paper and clothing (particularly if soiled). Their desire for fermented liquids, such as beer, is very strong. They will often travel for food, but adults with a water source can survive for 2-3 months without it.
American cockroaches usually congregate in warm, moist, dark locations. They prefer coastal areas, but are a widespread pest, living indoors in cool regions, and outdoors in warm regions. Buildings commonly infested include hospitals, bakeries, food stores, factories and houses. They tend not to infest dwelling areas in buildings, but rather the roof, wall and subfloor areas, and in and around sewers, grease traps and rubbish dumps.
Australian cockroach (Periplaneta australasiae)
These are darkish-brown cockroaches, about 35 millimetres long with yellow markings on the upper part of the thorax and on the fore margins of the forewings. Females produce up to 20 egg cases, each containing up to 24 eggs. Development takes 6-12 months and adults live for 4-8 months.
Australian cockroaches are most commonly found in warm sub-tropical to tropical environments and usually live outside in greenhouses, in and around shrubs and trees, around woodpiles and under bark or leaf litter in gardens. They sometimes come indoors and will inhabit subfloor, wall and roof voids. They prefer food of plant origin, becoming a pest when they enter homes and eat holes in clothing and books.
As Australian cockroaches are usually found outdoors, applications of insecticides to foundation plantings, woodpiles and mulch may be required. Residual barrier sprays can substantially reduce Australian cockroach populations around houses. Dusting sewage lines, roof and wall voids is an effective method of control if Australian cockroaches are infested in these areas. Baits and other formulations better suited for damp locations can provide control in cellars and greenhouses.
Smokybrown cockroach (Periplaneta fuliginosa)
Smokybrown cockroaches are about 30 millimetres long, a shiny dark brown-black colour and fully winged. Egg cases contain up to 26 eggs and are dropped or glued to surfaces. When hatched, nymphs take 6-12 months to develop to adulthood. Adults live for 6-12 months, during which time females produce up to 17 egg cases.
Smokybrown cockroaches are susceptible to losing moisture through their cuticle, and so are usually found in damp, dark, poorly ventilated environments. They rarely infest the dwelling parts of buildings, and are instead found in sheds, wall and roof voids, subfloors, mulched areas, in and around grease traps and in drains. They prefer food of plant origin, and are therefore often a pest in greenhouses, nurseries and gardens. They can fly short distances in warm weather, and are often attracted to lights at night.
Brownbanded cockroach (Supella longipalpa)
Brownbanded cockroaches are small (10-15 millimetres long) and pale glossy brown with very pale bands across the thorax and abdomen. These bands may appear irregular or broken, but are usually quite apparent on nymphs and females. Nymphs and females are broad when viewed from above, while the male is slender. The male’s wings extend beyond the abdomen but the female’s wings are smaller, exposing the abdomen, whereas nymphs have underdeveloped wings. Females produce up to 13 yellow to reddish brown egg cases, which may contain up to 18 eggs. They are usually carried around for 1-2 days before being glued to surfaces. Development from nymph to adult takes only 2-4 months and adults usually live for 3-6 months.
Brownbanded cockroaches tend to be an indoor pest. They like to feed on starchy materials such as books and wallpaper paste, but have also been known to eat clothing items such as nylon stockings. They hide in warm areas near the ceiling, behind wall decorations and loose wallpaper, in piles of paper in cabinets, beneath or inside upholstered furniture, and in electrical appliances such as stereos, and toasters. Activity may be scattered throughout the building, making control difficult.
These cockroaches may leave tiny, dark droppings and cast skins on cabinets and shelves. They are commonly transported in furniture, luggage, and other items in houses and can develop into persistent infestations during warm, humid conditions. It is not unusual to see them during the day. They are active and may fly in warm conditions, or if disturbed.
When locating these insects, look for faecal smears, cast skins, alive or dead individuals and egg cases glued to places in higher and drier areas than other cockroaches normally occupy. Brownbanded cockroach control often requires extensive treatment throughout an entire building, with particular attention to furniture, cupboards, bookshelves and other such harbourages.
Oriental cockroach (Blatta orientalis)
Oriental cockroaches are of medium size (20-25 millimetres long) and are uniformly dark brown to black. Male wings cover most of the abdomen, female wings are reduced, and nymphs have no wings. These cockroaches generally do not fly. The female may produce up to 14 egg cases in her lifetime, each containing up to 16 eggs. She carries her egg case around for about one day before gluing it to a surface. Nymphal development may take 6-18 months and adults live for 3-6 months
Oriental cockroaches prefer cool climates and are often found outdoors under leaf litter and bark, in damp subfloors and around drainage systems. They are relatively sluggish and are usually located at or below ground level in buildings where they eat a range of decaying organic matter. Starches and books may also be attacked.
Inspections for these cockroaches should concentrate in areas of high humidity and cool temperatures. Cellars, crawl spaces, and around plumbing in kitchens and bathrooms should be inspected for faecal smears, live or dead cockroaches and egg cases
Reviewed 20 December 2021