Successful control of cockroaches is a complex subject, and depends very much upon tailoring control measures to the species concerned.
Assessment of infestations
Assessment of species type is best carried out at night. A pyrethroid-based aerosol sprayed around and into potential hiding places will flush out species other than B. orientalis.
A high standard of hygiene will deny sources of food and hiding places.
(b) Insecticidal control
The technician will use a specialised bait gel that attracts the roaches. Once ingested, the bait gel will poison and kill any cockroaches that have eaten it. Since these insects are omnivorous, the live ones will feed on the dead, resulting in a domino effect over the cockroach population.
If the infestation level is high, the cockroach exterminator will use a powerful insecticide to spray the affected areas. The insecticide has a residual effect which means it will remain active over time.
Effective treatment depends upon the selection of a suitable insecticide and 1 subsequent thorough application. Many insects and egg cases are well hidden; 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 be used until all egg cases have hatched but continued activity may demand further routine treatments.
Space Spray Insecticides
To control an infestation using this technique it may be necessary to carry out a "blitz" treatment, spraying at least weekly until the infestation is brought under control. Thereafter, maintenance treatments, at less frequent intervals, should keep the insect population at an acceptable level. Initially there will be a massive kill of adults and nymphs resulting in only the appearance of young nymphs from time to time.
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Order: Dictyoptera ("net-winged")
Characteristics: generally two pairs of wings, although these may be reduced or even absent; fore wings have well developed veins and tend to be hardened, they overlap down the mid-dorsal line; membranous hind wings are folded below fore wings; long, whip-like, many-segmented antennae; omnivorous, with mouth parts adapted for biting; tarsi, 5 segmented; incomplete metamorphosis, with egg and nymph stages.
Oriental Cockroach (Blatta orientalis)
Adult, 20-24mm long; dark-brown, nearly black in colour; wings of male cover two-thirds of abdomen, wings of female are vestigial; can climb rough but not smooth vertical surfaces.
German Cockroach (Steamfly) (Blattella germanica)
Adult, 10-15mm long; yellowish-brown in colour with two longitudinal dark marks on pronotum; wings well-developed in both sexes; can readily climb rough and polished vertical surfaces.
The nymphs of all species are similar in appearance to the adult but smaller. Immediately after hatching or moulting the nymphs are white, but the cuticle soon darkens to the adult colour.
Cockroaches are potential vectors of diseases such as dysentery, gastroenteritis, typhoid and poliomyelitis. Their diet is omnivorous and includes fermenting substances, soiled septic dressings, hair, leather, parchment, wallpaper, faeces and food for human consumption. (An outbreak of food poisoning in a Brussels hospital subsided immediately when infestation of B.germanica was controlled.) The latter may be contaminated either by the mechanical transfer of causative agent disease from the insect's body, or by transmission in the faeces. 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.
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 in the vicinity of a food supply. They may then be covered over with debris. Nymphs emerge 612 weeks later and progress through 7-10 moults before reaching maturity, a process which takes 10 months-2 years depending upon temperature and food supply. With each successive moult the wings, antennae and cerci develop and the nymph becomes progressively more like the adult. Adults live approximately 4.5 months at 25°C.
The slow proliferation of B.orientalis will limit its success where reasonable standards of hygiene exist.
The female of this species produces 4-8 egg capsules at approximately 1-month intervals. Each thick-walled resistant capsule is 6mrp long and contains up to 30 eggs, but unlike B.orientalis, the female carries the capsule until just before the eggs hatch- some 2.5 - 4 weeks later. 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 25°C maturity is reached in 3.5 months, but this time can be profoundly influenced by temperature.
Adults live approximately 8.5 months at 25°C.
The German cockroach is particularly successful for the following reasons:
1. A large number of eggs per capsule;
2. The female protects the egg capsule, by carrying it until just before hatching; 3. short development period to hatching and maturity;
4. Small size, therefore readily conceals itself.
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