Cockroaches (Insecta: Blatteria) are stated as one of oldest and is the most adaptable insect group so far in the human history. It has been surviving on the earth from 300 million years. Almost 3500 species of cockroaches have been found and of these 50 are synanthropic i.e. they are always present around humans making them an insect of public health and epidemiological significance.
By Aarzoo Ashraf,Muhammad Sohail Sajid,Muhammad Hamza Rasool
Their involvement in transmission of several diseases started a debate of completely classifying them as vectors. Though cockroaches are omnivore in nature, they have been reported as non-offensive biting insects and cause no harm to structures inside houses. But among all households‟ pests, cockroaches cause immense health threat to humans as they can eat anything without discrimination, can survive without feeding for many weeks and have capability of breeding all around the year. Also, their nocturnal activity, acclimatization to all kinds of climatic conditions and wide range of habitats, possibly make them prevalent.
Taxonomy of Cockroaches
Thirty five hundred species and over four hundred sixty genera of cockroaches have been identified yet and among all these, thirty species are found to beliving around human dwellings and associated with human beings. B.germanica (German cockroach), P. americana (American cockroach) and B. orientalis (oriental cockroach) are among the abundantly distributed species. Under the Kingdom Animalia, cockroaches belong to Phylum Arthropoda, Subphylum Hexapoda, Class Insecta and Order Blattodea. Previously, Blattaria was used interchangeably with the Blattodea but former is used to refer to „true‟ cockroaches exclusively while latter also includes termites.
Morphology of Cockroaches
The common pest species are dark brown or black, 15–45 mm long, dorso ventrally flattened and have a tough and shiny integument. The head is small and hidden by pronotum. A pair of long antennae arises between the eyes. Mouth parts of cockroach are developed for gnawing, chewing and scrapin. Both male and female have two pairs of wings. In some species wings of female are shorter than male. Forewings of the cockroach are called “Tegmina”. They are thick and leathery. Forewings are not used in flight but used for the protection of hind wings. Although hind wings can be used for flying, cockroaches fly rarely. The legs are covered with bristles and spines.
Life Cycle of a Cockroach
A cockroach life cycle includes three stages-egg, nymph and adult. Female cockroach can lay up to 6-40 eggs at a time depending on species and encapsule them in a leathery, bean-shaped egg case or capsule called ootheca. An average of 10-14 eggs is present in each ootheca. For their protection, oothecas are deposited in cracks or crevices with secretions from the female‟s mouth or cemented them under tables, chairs and beds until the eggs hatch. Nymph is the next stage in cycle which pass through process of molting until becomes an adult. After each molting, the nymph gets larger in size and undergoes color changing. Nymphal instars varies not only between but also within species and ranges from 5-7 but they can be as many as 13, as sometimes in case of P. americana. Nymphs are pale and grayish brown in color just after hatching but after few molts become reddish brown. Adult cockroaches are similar in shape to nymph except they have a pair of fully developed wings. When get ideal conditions, a female can have a life of 15 months and during this period they can lay 4-90 oothecas depending on species while the males however have shorter life span. The severity of an infestation can be identified from the life cycle of a cockroach.
Habitat of Cockroaches
The migratory ability of cockroaches is tremendous. They can travel anywhere even in mini cracks and small crevices in ceiling boards and walls, through heating and air vents and can reach on elevator shafts and drains. They widely present in areas having plenty of food sources such as restaurants, kitchens, pantries, cafeterias and places where garbage is collected or disposed. In such hot conditions they found places that are dark, humid and shady such as septic tanks, refuse tips, underneath chairs, bath sand beds, cesspits, tables, cupboards, sewers, refrigerators, refuse tips, cooking stoves and dustbins.
Public Health Importance of Cockroaches
The presence of cockroaches in a bacteria-rich environment having pathogenic and potentially pathogenic bacteria is more harmful than in a bacteria-poor environment. People with low level immunity are more at risk of getting diseases and bacterial contamination from cockroaches. Many of the pathogenic species of bacteria are potential pathogens or opportunist and are risk factor for human health; hence their presence also indicates the reduced sanitation level in human dwellings. Although the bacterial species isolated from cockroaches trapped from hospitals are morea ntibiotic resistance, which is considered more serious. They can also be dangerous in food-handling establishments if they are transmitting pathogenic bacteria.
Cockroaches are considered as one of the most significant agent in transmitting either mechanically or biologically almost 45 species of parasitic worms, 90 protozoal species, 150 species of bacteria and 60 yeast species. In many areas the presence of cockroaches results in higher frequency of diarrheal cases and are also linked with many other ill-health problems by carrying different pathogens that cause cholera, typhoid fever, dysentery, poliomyelitis, leprosy, food poisoning and parasitic worms as well. The diseases caused by the pathogenic bacteria are dysenteries, gastroenteritis, enteric fever, food poisoning, typhoid fever, gas gangrene and leprosy.
Control Measures
It is easier to effectively control cockroaches in temperate climates rather than in areas having warm and humid climate. The key to control their population is by maintaining cleanliness which is hard to achieve in houses with children and domestic animals and reducing their accessibility which is easier to achieve in isolated houses than in apartments. Reinfestation can result from luggage and groceries brought from areas that are cockroach infested, from outdoors in warm weather and in apartments from water ducts and heating pipes. The control strategies for cockroaches differ in private dwellings than in public establishments. Elimination of cockroaches from sensitive areas is taken into consideration. Their control in human dwellings and food-handling establishments is possible by maintaining acceptable hygiene standards. High infestation can be controlled by chemical control and by depriving the insects of shelter and food through environmental management. Appropriate use of insecticides is also a essential weapon against their eradication.
Authors:
- Aarzoo Ashraf, M.Phil. Epidemiology and Public health, University of Agriculture, Faisalabad.
- Muhammad Sohail Sajid, Associate professor of Parasitology, University of Agriculture, Faisalabad.
- Muhammad Hamza Rasool, M.Phil. Epidemiology and Public health, University of Agriculture, Faisalabad.