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An Introduction to Medical Entomology

For educational purposes.






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Also See: <Blattaria Key>


The order Blattaria are the cockroaches, sometimes called "water bugs", which have been transferred from the Orthoptera to a separate order. They have generalized biting mouthparts and a five-jointed tarsus. They are considered as probably the oldest group of present day insects. The anterior wings are narrower and stouter than the posterior ones, which are more membranous and fold like a fan. Jointed cerci & styles occur in adult males only. The ovipositor is small or absent. The metamorphosis is hemimetabolous. Eggs are laid in beanlike capsules or oothecae that are produced by secretions of female accessory glands. The female may deposit these all at one time, or they may be carried around until they hatch. Cockroaches are nocturnal in their habits and omnivorous. They are also gregarious.

All cockroaches are insects of substantial size. They have dorsoventrally flattened bodies, a pronotum, which is large, wide, or shield-like, and powerfully developed legs for rapid running. The coxae are broad so as to protect the lower surface of the body.

They are commonly in tropical or subtropical insects although they have adapted to living in dwellings in temperate zones. Their mouthparts indicate their omnivorous habit, as also is their alimentary canal. Strongly cuticularized toothed mandibles are followed by prominent maxillae, each of which bears a five-jointed palp, a toothed setose lacinia and a sensory flexible galea. The labium has a four-lobed ligula consisting of a pair of small glossae flanked by larger paraglossae. The labial palps are three-jointed.

     The alimentary canal has a pair of salivary glands developed on the labial segment, which secrete amylase. A huge thin-walled crop leads into a gizzard-like proventriculus, the inner lining of which is provided with prominent cuticular jaws and spiny pads. These, worked by circular and longitudinal muscles, break up the food into fine particles and to filter it in its passage to the mid gut.

      The mid gut is the site of the formation of a full complement of enzymes suitable to the mixed diet on which the animals feed. Examples are the cockroaches
Periplaneta americana and P. australasiae and the less common German cockroach, Blattella germanica and Oriental roach, Blatta orientalis.




Cockroaches seek out warm and humid areas where as omnivores they feed on any available food. They move among dwellings via sewers They are able to survive for many weeks without water and months without food. In their hemimetabolous life cyele the nymphs emerge from eggs after 1-3 months of incubation, but varying with temperature. They wingless nymphs have a variable number of instars of 5-13, depending on species and environment. The length of time for each stage depends also on species and environmental conditions.




The grasshopper and crickets are not of importance in spreading disease, but their vast numbers at times may cause great distress to humans by flying into them, getting in clothes and accumulating in public buildings during autumn especially.


However, cockroaches that were included in the Orthoptera before being assigned to their own order Blattaria, are of great importance in spreading disease as they harbor pathogens on their oily bodies. They enter food preparation areas at night, contaminating utensils, and they can move through sewers between dwellings transferring disease-causing organisms in the process. Regarding allergies, Service (2008) noted that the allergic rate is second only to that caused by house dust mites.


Cockroaches have been found to carry a number of diseases, among which are Poliomyelitis virus, Entamoeba histolytica, Klebsiella pneumoniae, Toxoplasma gondii, Escherichia coli, Staphylococcus aureus, Salmonella. and Shigella dysentariae



Cockroaches may be controlled with poisoned baits, but sanitation is the most effective way to reduce their invasion into home areas. However, neighboring dwellings that harbor large populations of roaches may pose a threat because they are able to travel through the sewer system. Service (2008) recommended the application of synthesized insecticidal sprays or dusts to areas in the dwelling where cockroaches roam. However, the continuous use of such products inevitably leads to resistance and reduced effectiveness. Some of the older natural remedies such as boric acid powder have provided good control both as a stomach poison and contact insecticide. Poisoned baits include nicotine or sulfonamide based substances mixed with various foods (e.g., peanut butter that should be set in areas where cockroaches are observed. Available also are sticky traps containing cockroach pheromones.

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Key References: <medvet.ref.htm> <Hexapoda>


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