Unhygienic scavengers in human settlements Cockroaches are among the foremost common pests in many homes and other buildings. in the dark they look for food in kitchens, food storage places, rubbish bins, drains, and sewers. they're pests due to their filthy habits and bad smell. Some people may become allergic to cockroaches after frequent exposure. Cockroaches can sometimes play a task as carriers of intestinal diseases, such as diarrhea, dysentery, typhoid, and cholera. Biology Cockroaches are insects, flattened from top to bottom, usually with two pairs of wings folded flat over the rear
(Fig. 5.1). Most species rarely fly but they walk very fast. the color usually varies from brown to black. The species vary from 2– 3mm to over 80mm long. Of over 3500 identified species only a couple are of importance to people because they have adapted to living in buildings. the foremost common species are • American cockroach, the American cockroach, which occurs around the world. it's 35–40mm long and maybe a shiny reddish to chocolate brown colour
(Fig. 5.2a). The egg case measures 8–10mm and contains 16 eggs. • Australian cockroach, the Australian cockroach, occurs mainly in tropical and subtropical areas. it's almost like the American cockroach, but smaller (31–37mm long) and darker (Fig. 5.2b). it's a straw stripe on each forewing extending for about one-third its length. The egg case contains about 22–24 eggs. • oriental cockroach, the oriental roach, is found mainly in cool temperate regions. it's blackish and 20–27mm long
(Fig. 5.2c). The egg case is 10– 12mm long and contains 16–18 eggs. • Supella longipalpa, the brown-banded cockroach, which occurs around the world. it's 10–14mm long and has yellow and brown bands (Fig. 5.2d). The egg case is 4–5mm long and contains about 16 eggs. • German cockroach, the German cockroach, found in most parts of the planet. It is light raw sienna and 10–15mm long, making it one of the smallest domestic cockroaches
(Fig. 5.2e). the feminine usually carries the egg case until shortly before the young beginner. The egg case is light in color, about 7–9mm long and contains about 40 eggs. Life cycle Cockroaches are relatively primitive, having only three stages in their life cycle: egg, nymph, and adult (Fig. 5.3). the feminine deposits its eggs in groups surrounded by a leathery, bean-shaped egg case or capsule called an ootheca. Some BIOLOGY 289 Fig. 5.1 Side view of a cockroach (Blattella germanica) (© WHO).
Fig. 5.2 The most common cockroach species: (a) American cockroach, Periplaneta americana; (b) Australian cockroach, Periplaneta australasiae; (c) oriental roach, Blatta orientalis; (d) brown-banded cockroach, Supella longipalpa; (e) German cockroach, German cockroach (by courtesy of the Natural History Museum, London). BIOLOGY 289 290 CHAPTER 5 • COCKROACHES species, like the German cockroach, carry the ootheca for several weeks attached to the rear end of the body.
Most others deposit the ootheca after one or two days. Oothecae are very distinctive and may frequently be wont to determine the species present. counting on the species, temperature, and humidity, the eggs hatch after 1–3 months.
The young cockroaches, or nymphs, are wingless, and typically only a couple of millimeters long; they're white on hatching but darken within a couple of hours. They grow piecemeal by repeatedly shedding the cuticle or skin. they're adults after several months to quite a year, counting on the species. The adults may or might not possess wings, consisting of 1 outer leathery pair beneath which is folded a membranous pair. Behaviour Pest cockroaches sleep in close association with people (1, 2).
they're tropical in origin but within the temperate zones, most species sleep in parts of homes and other buildings where warmth, moisture, and food are adequate. Cockroaches usually sleep in groups. they're mostly active at night; within the daytime, they hide in cracks and crevices in walls, door frames, and furniture, and insecure places in bathrooms, cupboards, steam tunnels, animal houses, basements, televisions, radios, and other electric devices, drains and sewer systems.
If the lights are turned on in an infested kitchen in the dark the cockroaches will run from dishes, utensils, work surfaces, and therefore the floor towards shelter. Fig. 5.3 Life cycle of the German cockroach (by courtesy of the explanation Museum, London). BIOLOGY 291 Fig.
5.4 Uncovered garbage bins offer an excellent environment for cockroaches to develop (© WHO).
Cockroaches eat an excellent sort of food, including all food used for human consumption (Fig. 5.4). they like starchy and sugary materials. They sip milk and nibble at cheese, meats, pastry, grain products, sugar, and sweet chocolate.
They also prey on cardboard, book bindings, ceiling boards containing starch, the sized inner lining of shoe soles, their own cast-off skins, dead and crippled cockroaches, fresh and dried blood, excrement, sputum, and therefore the fingernails and toenails of babies and sleeping or sick persons. Dispersal Mass migrations are reported for a few species, apparently resulting from overcrowding. The migrants enter new areas by crawling or flying. They commonly enter houses in boxes of bottled drinks and bags of potatoes, onions, or other foodstuffs that became infested in poorly maintained food stores.
Long-distance transportation of the pests can occur on aircraft, ships, or other vehicles. Public health importance Nuisance Cockroaches are important pests because they spread filth and ruin food, fabrics, and book-bindings. They disgorge portions of their partially digested food at intervals and drop feces.
They also discharge a nauseous secretion both from their mouths and from glands opening on the body which provides a long-lasting, offensive cockroach smell to areas or food visited by them. Diseases Cockroaches move freely from building to putting together or from drains, gardens, sewers, and latrines to human habitations. Because they prey on human feces also as human food they will spread germs that cause disease (Fig. 5.5) (2, 3). Cockroaches aren't usually the foremost important explanation for a disease, but like houseflies BIOLOGY 291 292 CHAPTER 5 •
COCKROACHES Fig. 5.5 Cockroaches can spread disease by contaminating human food with germs they devour in latrines, garbage dumps, etc. they may play a supplementary role within the spread of some diseases. They are proven or suspected carriers of the organisms causing: — diarrhea — dysentery — cholera — leprosy — plague — typhoid — viral diseases like poliomyelitis. In addition, they carry the eggs of parasitic worms and should cause allergic reactions, including dermatitis, itching, swelling of the eyelids, and more serious respiratory conditions (4).
Control measures Effective control is simpler in temperate climates (where cockroach populations cannot survive outdoors in winter) than in humid and warm areas. The key to control is cleanliness, which can be difficult in houses where there are children and livestock. In isolated homes, control is simpler to realize than in apartments where cockroaches may have quick access from adjacent quarters. Reinfestation occurs from outdoors in warm areas, or along heating ducts and water pipes in apartments, or from groceries or luggage brought from cockroach-infested areas.
Cockroaches may even sometimes be found in very clean houses, but are unlikely to determine colonies. The presence of several sizes of nymphs and oothecae is a sign of a wellestablished colony. Infestations are often detected by searching behind skirtingboards, boxes, furniture and other common hiding places.
At night, cockroaches are easily detected using light. BIOLOGY 293 Heavy infestations of cockroaches are often addressed by chemical control measures, followed by environmental management to deprive the insects of food and shelter.
Low numbers are often effectively controlled by baits or traps. Environmental management Cleanliness and hygiene Food should be stored in tightly covered containers in screened cabinets or refrigerators (Fig. 5.6). All areas need to be kept clean in order that no fragments of food or organic matter remain.
Rubbish bins should be securely covered and emptied frequently, preferably daily. Basements and areas underneath buildings should be kept dry and freed from accessible food and water. Reduction of accessibility Groceries, laundry, dirty clothing, egg crates and furniture should be checked before being taken into a building. In some instances, accessibility to buildings are often reduced by closing gaps in floors and door frames. Openings for drain water and sewer pipes, drinking-water and electricity cables should even be closed
(Fig. 5.7). Chemical control Cockroaches are difficult to regulate with insecticides for several reasons, one of which is that they'll become immune to commonly used compounds. Moreover, many insecticides are repellent to them and are therefore avoided (5).
Chemical control gives only temporary relief and, wherever possible, it should be accompanied by environmental sanitation and house improvement (6). Fig. 5.6 Food are often protected during a cockroach-, fly- and ant-proof cabinet. CONTROL MEASURES 293 294 CHAPTER 5 • COCKROACHES Fig. 5.7 Reduce accessibility to cockroaches by sealing openings, cracks and crevices.
Insecticides are applied to the resting and hiding places as residual sprays and insecticidal dusts. Such applications are effective for periods starting from several days to months, counting on the insecticide and therefore the substrate on which it's deposited.
Insecticides also can be combined with attractants as toxic baits. Resistance The German cockroach is immune to several organochlorine, organophosphorus, carbamate and pyrethroid insecticides (7). The oriental roach, the American cockroach and therefore the large brown cockroach (Periplaneta brunnae) have developed little resistance, mainly to DDT and chlordane.
Recently, the American cockroach has been found to be immune to trichlorfon in China and therefore the large brown cockroach to diazinon within the USA. Application Areas to be treated Areas to be treated include kitchens, galleys, behind and along skirting-boards, in and around sinks, in or under cupboards, under chairs and tables, in utility cabinets, near refrigerators and ice boxes, under loose floor coverings, food prepa- BIOLOGY 295 ration areas, ducts, pipes, sewers and manholes. Food storage areas in restaurants, warehouses and other commercial establishments should be treated.
Frequency of treatment How long the deposits of insecticide remain effective depends on variety of factors, like the thoroughness of application, the speed of re-infestation, the chemical used, the dosage and formulation applied, the sort of surface to which it is applied, the temperature and humidity, and therefore the amount of wearing or rubbing off that happens.
Insecticides generally last longer on painted than on unpainted surfaces and longer on wood than on brick or block surfaces. Frequent washing of a treated surface or coatings of dust or grease can render an insecticide useless.
one treatment rarely leads to eradication. For most species, additional treatments could also be necessary at monthly intervals to kill newly hatched nymphs or to stop reinfestation. Safety and precautions Care should be taken to avoid food contamination. Avoid treating areas where children may inherit contact with the residue. In special situations, like the treatment of zoos or pet shops, residual sprays or dusts can't be used.
In such cases it's going to be possible to use a limited quantity of chemical with a brush. Alternatively, a chemical with low toxicity to mammals and birds, like boric acid powder or silica aerogel, could also be used. Some formulations may stain fabrics, wallpaper, floor tiles or other household materials.
Information should be obtained on this subject before treatment is carried out. Residual sprays Residual sprays are usually applied with household plunger-type sprayers or handcompression air sprayers. The sprayers are equipped with pinstream nozzles to spray the insecticide into cracks and areas that are hard to succeed in. A broader fan spray is beneficial for areas that are more accessible.
The spray should moisten the surface thoroughly but to not the purpose of water running off or dripping. A volume of 4 litres of diluted insecticide per 100m2 sprayed in swaths 30–50cm wide is usually appropriate. The insecticide are often applied with a paint brush when other equipment isn't available. Thorough treatment of runways and harbourage areas is important for effective control. Usually, an important initial treatment is followed by periodic follow-up treatments.
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