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Cockroaches – Auf Wiedersehen Pest!!

21 Mar

Often confused with black beetles from the garden, cockroaches are distinguished by their very long whip-like antennae, flat oval bodies and rapid jerky running about.
The adult small brown German cockroach is 10 50 15mm long, and the Common or Oriental cockroach is 20 to 24mm long.
They are rarely able to survive out doors in the British climate but thrive around the heating ducts and boiler rooms of large centrally heated buildings, in hospitals, bakeries, hotel and restaurant kitchens, laundries and blocks of flats. They cluster around pipes, stoves and sinks, especially in humid areas.


Cockroaches are potential vectors of diseases such as dysentery, gastro-enteritis, typhoid and poliomyelitis. Their diet is omnivorous and includes fermenting substances, soiled septic dressings, hair, leather, parchments, wallpaper, faeces and food for human consumption. Cockroaches and their faeces may cause allergic reactions especially amongst sensitive individuals e.g. asthmatics. Exposure may result from ingestion or through the inhalation of materials derived from cockroaches in airborne dust. In addition, food may be tainted with the characteristic smell of the cockroach, which is produced by faeces and salivary/abdominal gland secretions, or by the dead insects.

Life Cycle

Oriental cockroach

17-30 mm, dark brown to black very shiny and very flattened, the female has very reduced wing buds and the male wings are longer to almost the end of the abdomen. They have long flexible antennae.The female produces 5 egg capsules at monthly intervals. The thick-walled resistant capsules, 12mm in length, each contain up to 16 eggs and are cemented to the substrate or dropped in the vicinity of a food supply. This may then be covered over with debris. Nymphs emerge 6-12 weeks later and progress through 7-10 moults before reaching maturity, a process that takes 10 months to 2 years depending upon temperature and food supply. With each successive moult the wings, antennae and cerci (paired appendages located at the tip of the abdomen) develop and the nymph becomes progressively more like the adult. Adults live approximately 4.5 months at 25C. They are prevalant in heated buildings, dustbin areas, waste/compactor areas, cellars, boiler houses, ductings, lift shafts. Colonies are often established in drains or services but sometimes in cladding and dead spaces inside processing equipment. They can squeeze into very small cracks and will exploit bad fitting coving and door jams etc. One of the main routes into premises is via laundry suppliers off site. This species cannot fly but it is very fast running. It cannot climb smooth surfaces.

German cockroach

12-15mm, mid brown, with a yellow brown thorax having two dark brown stripes. Long antennae. Wings full length in male but 2/3 length in the female.The female of this species produces 4-8 egg capsules at approximately 1-month intervals. Each thick-walled resistant capsule is 6mm long and contains up to 30 eggs. Efforts are made to conceal the capsules near a food source, where the nymphs will hatch and pass through 5-7 moults before reaching maturity. At a temperature of 25C maturity is reached in 3.5 months, but this time can be profoundly influenced by temperature. Adults live approximately 8.5 months at 25C. The insect prefers a warm moist environment, inside switch boxes, motor housings, panels inside machines, fridge motors, conduits etc. The insect is often found in steamers and around the linings of provers, it can also exploit small gaps squeezing into joints. It will take up residence inside drink dispensing machines, optics, beer and drink coolers, hollow legs of tables and equipment. It can sometimes be found behind door seals and in voids.

It can swim and will climb smooth surfaces easily. Once established in food catering or manufacturing premises this insect is often difficult to eradicate, this is due to it hiding in inaccessible places. Sometimes when found inside plant and machinery it is not brought under control until the equipment is totally dismantled and cleaned.

The German cockroach is particularly successful for the following reason:

  • A large number of eggs per capsule.
  • The female protects the egg capsule by carrying it until just before hatching.
  • Short development period to hatching and maturity.
  • Small size therefore readily conceals itself.

Control of Infestation

Cockroach traps should be sited to determine the extent and seat of the infestation. Their ability to find harbourages inside catering equipment, inside bottle washers and switchgear is well chronicled. To determine infestation a night inspection is recommended and insects can be easily flushed from their harbourages using a pyrethroid based aerosol spray can such as Insectrol Insect Killer

a) Hygiene/management

A high standard of hygiene is important in the control of cockroaches and involves the following components:

  • Deny access to food and water. This will increase cockroach activity and directed movement improving the opportunity for the insects to encounter insecticides.
  • Deny access to harbourages in buildings or equipment that would otherwise provide hiding places, a means of gaining access and dispersing and breeding sites.
  • Ease of cleaning. Buildings and equipment should be designed to minimise the accumulation of debris and facilitate ease of cleaning.
  • Surveillance of incoming materials including packages and laundry.

b) Insecticidal control

Surface Sprays
Treatment should be to wall/floor and wall/ceiling junctions as appropriate with a residual insecticide such as the aforementioned Insectrol or Dethlac Lacquer. Attention should be paid to very small cracks, crevices, broken tiles, poor fitting door frames, gaps around pipes entering walls and guards on wall corners. These insects will get inside hollow legs of equipment and tables, inside machine dead spaces, trunking, switches, electrical motors, coolers, fridge motors and drinks machines/ dispensers. Some of these can be treated with care with an insecticide. In the case of electrical items you might be best to flush with an aerosol and band the area around them with the preparation. Contact dust such as a dehydrating silica gel can be used in voids as long as there is no danger of cross contamination.
Effective treatment depends upon the selection and thorough application of the insecticide. Many insects and egg cases are well hidden; therefore the insecticide must be placed at and around these harbourages and maintained over the developmental period of the particular species. To control an infestation the insecticide should ideally persist until all egg cases have hatched but continued immigration may demand routine treatments.

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