COCKROACH

Introduction Cockroach is an insect of the order Dictyoptera. The body is flattened from top to bottom and oval in outline. The male usually has two pairs of wings folded flat over the back, consisting of one outer leathery pair beneath which is folded a membranous pair, whereas the female, in some species, is wingless or has vestigial wings. Most species rarely fly but they walk very fast. The colour usually varies from light brown to black. The species vary from 2 – 3 mm to over 80 mm in length. The head is bent downward and is protected by the enlarged flanges of the thorax. The mouthparts point backward instead of forward or downward as is the case in most other insects. Their long, hair-like, highly sensitive antennae and sensory bristles enable them to detect tiny amounts of food and moisture. The cerci, sensory structures extending from the rear of the abdomen, can sense minute air movements, enabling the cockroach to rapidly detect and flee from potential danger. Most cockroaches are difficult to catch due to their soft, slippery outer skin, called the cuticle. The oily cuticle also protects them from dehydration. Some species, including the Madeira cockroach, can produce sound. The cockroach prefers a warm, humid, dark environment and is usually found in tropical or other mild climates. The insect damages more material than it consumes and emits a disagreeable odour. The diet of the roach, which includes both plant and animal products, ranges from food, paper, clothing, and books to dead insects, especially bedbugs. Of over 3500 identified species only a few are of importance to people because they have adapted to living in buildings. The most common species are: • The American cockroach (Periplaneta americana) occurs around the world. It is 35 – 40 mm in length and is shiny reddish to chocolate brown colour. It has well-developed wings, but not a good flyer. The egg case (ootheca) measures 8 – 10 mm and contains 16 eggs. It lives outdoors or in dark, heated indoor areas (e.g., basements and furnace rooms). During adult life, a period of about 1.5 years, the female deposits 50 or more oothecae that hatch after 45 days. Nymphal life lasts from 11 to 14 months. • The German cockroach (Blattella germanica) is found in most parts of the world. It is light yellowish brown and 10 – 15 mm in length, making it one of the smallest domestic cockroaches. The female produces the ootheca three days after mating and carries it for about 20 days. The egg case is light in colour, about 7 – 9 mm long and contains about 40 eggs. Three or more generations may occur yearly. • The brown-banded cockroach (Supella longipalpa) resembles the German cockroach but is slightly smaller and occurs around the world. It is 10 – 14 mm long. The egg case is 4 – 5 mm in length and contains about 16 eggs. The male has fully developed wings and is lighter in colour than the female, whose wings are short and non-functional. Both sexes have two light-coloured bands across the back. The adult life span is about 200 days, and there may be two generations annually. • The Oriental cockroach (Blatta orientalis) is considered one of the filthiest of household pests. It is found mainly in cool temperate regions. It is blackish and 20 – 27 mm long, with a life cycle similar to that of the American cockroach.. The egg case is 10 – 12 mm long and contains 16 – 18 eggs. The male has short, fully developed wings, and the female has vestigial wings. • The Australian cockroach (Periplaneta australasiae) occurs mainly in tropical and subtropical areas. It is similar to the American cockroach, but smaller (31 – 37 mm long) and darker. It has a pale yellow stripe on each forewing extending for about one-third its length. The egg case contains about 22 – 24 eggs. Life Cycle Courtship patterns vary with the species. When the American cockroach is ready to mate, the female produces a chemical odour, or pheromone, that attracts males. The males flap their wings and probe for females with their abdomens when they sense the pheromone; eventually, they back into a female and mating ensues. Other species have more elaborate mating displays, including hissing noises, bobbing and waving of the abdomen, or nibbling. The males of one African species form dominance hierarchies, and the females preferentially mate with the dominant male. Cockroaches are relatively primitive, having only three stages in their life cycle: egg, nymph and adult. The female deposits its eggs in groups surrounded by a leathery, bean-shaped egg case or capsule called an ootheca. Some species, such as the German cockroach, carry the ootheca for several weeks attached to the back end of the body. Most others deposit the ootheca after one or two days. Oothecae are very distinctive and can frequently be used to determine the species present. Depending on the species, temperature and humidity, the eggs hatch after 1 – 3 months. The young cockroaches, or nymphs, are wingless, and usually only a few millimetres long; they are white on hatching but darken within a few hours.They undergo gradual metamorphosis—that is, they grow and mature in stages, each separated by a moult of the exoskeleton. Each successive stage, or instar, comes to resemble the adult insect more and more. They are fully grown after several months to more than a year, depending on the species. The adults may or may not possess wings, Behaviour Pest cockroaches live in close association with people. They are tropical in origin but in the temperate zones most species live in parts of houses and other buildings where warmth, moisture and food are adequate. Cockroaches usually live in groups. They are mostly active at night; in the daytime they hide in cracks and crevices in walls, door frames and furniture, and in secure 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 at night the cockroaches will run from dishes, utensils, working surfaces and the floor towards shelter. Cockroaches eat a great variety of food, including all food used for human consumption. They prefer starchy and sugary materials. They sip milk and nibble at cheese, meats, pastry, grain products, sugar and sweet chocolate. They also feed 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 the fingernails and toenails of babies and sleeping or sick persons. Dispersal Mass migrations have been reported for some species, apparently resulting from overcrowding. The migrants move into new areas by crawling or flying. They commonly enter houses in boxes of bottled drinks and bags of potatoes, onions or other foodstuffs that have become 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 faeces. They also discharge a nauseous secretion both from their mouths and from glands opening on the body which give a long-lasting, offensive cockroach smell to areas or food visited by them. • Diseases: cockroaches move freely from building to building or from drains, gardens, sewers and latrines to human habitations. Because they feed on human faeces as well as human food they can spread germs that cause disease. Cockroaches are not usually the most important cause of a disease, but like houseflies they may play a supplementary role in the spread of some diseases. They are proven or suspected carriers of the organisms causing: diarrhoea, dysentery, cholera, leprosy, plague, typhoid fever and viral diseases such as poliomyelitis. In addition they carry the eggs of parasitic worms and may cause allergic reactions, including dermatitis, itching, swelling of the eyelids and more serious respiratory conditions. Control Measures Effective control is easier in temperate climates (where cockroach populations cannot survive outdoors in winter) than in humid and warm areas. The key to control is cleanliness, which may be difficult in houses where there are children and domestic animals. In isolated homes, control is easier to achieve than in apartments where cockroaches may have easy 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 establish colonies. The presence of several sizes of nymphs and oothecae is an indication of a well-established colony. Infestations can be detected by searching behind skirting-boards, boxes, furniture and other common hiding places. At night, cockroaches are easily detected using light. Heavy infestations of cockroaches can be dealt with by chemical control measures, followed by environmental management to deprive the insects of food and shelter. Low numbers can be effectively controlled by baits or traps. Environmental management • Cleanliness and Hygiene: food should be stored in tightly covered containers in screened cabinets or ferigerators. All areas have to be kept clean so 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 free of 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 can be reduced by closing gaps in floors and door frames. Openings for drain water and sewer pipes, drinking-water and electricity cables should also be closed. Chemical Control Cockroaches are difficult to control with insecticides for several reasons, one of which is that they may become resistant to commonly used compounds. Moreover, many insecticides are repellent to them and are therefore avoided. Chemical control gives only temporary relief and, wherever possible, it should be accompanied by environmental sanitation and house improvement. Insecticides are applied to the resting and hiding places as residual sprays and insecticidal dusts. Such applications are effective for periods ranging from several days to months, depending on the insecticide and the substrate on which it is deposited. Insecticides can also be combined with attractants as toxic baits. Scientific Classification Cockroaches make up the order Dictyoptera, which contains five families. The American cockroach is Periplaneta americana, and the Oriental cockroach is Blatta orientalis, both in the family Blattidae. The German cockroach, Blatella germanica, the Asian cockroach, Blatella asahinai, and the brownbanded cockroach, Supella longipalpa, are in the family Blatellidae. The Madeira cockroach is Leucophaea maderae, the Brazilian cockroach is Blaberus giganteus, and the Madagascar hissing cockroach is Gromphadorina portentosa, all in the family Blaberidae. The remaining families are the Cryptocercidae and the Polyphagidae.