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An Introduction to Medical Entomology

For educational purposes.


Arthropoda - Insecta




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[Also See: Blattaria Key]


Order Orthoptera


The order Orthoptera -- <Adults> & <Juveniles> --, meaning "straight-winged, are large insects and among the most injurious to plants of all insects. However, their medical importance is primarily in annoyance, especially when they assemble in large numbers in and around dwellings. They have biting mouthparts, and their hind legs have enlarged femora for jumping. The fore wings are straight and leathery and are modified as tegmina, which overlap each other, while the hind wings are fanlike. The cerci are unjointed and the pronotum has enlarged lobes that hide the pleural wall. The ovipositor is well developed, and there are specialized stridulatory organs.


This order includes grasshoppers, locusts and crickets. Among the grasshoppers are the katydid or long-horned grasshopper Tettigoniidae== <Habits>; <Adults> & <Juveniles> -- with large sword-like ovipositors consisting of three pairs of valves borne on the 8th and 9th abdominal segments. By means of these the eggs, not enclosed in an ootheca, can be deposited in plant tissues, on which these insects regularly feed. The antennae also are long, often extending backwards beyond the apex of the abdomen. Stridulation is brought about by rubbing a toothed ridge on the left tegmen against an analogous region of its right counterpart. This latter has a smooth tense membrane and acts as a resonator when the tegmina are in motion and the noise, produced mostly at night, can be very loud. Auditory organs of some complexity are situated in each fore tibia. The Mormon cricket, Anabrus simplex Haldeman, can be a serious pest of agricultural crops in the Intermountain western North America. A miracle of sorts occurred in Utah where a serious outbreak of these crickets was destroying agricultural crops, but which was significantly reduced by seagulls (Larus californicus) (Borror, D. J. et al. 1981).

  Other grasshoppers and locusts differ from these in their shorter antennae, which are hardly ever as long as the body, and in their less prominent ovipositor, the valves of which are short and curved. Rubbing the inner edges of the hind femora that bear pegs against the hardened veins on the tegmina produces stridulation in these short homed grasshoppers and locusts. The tegmina then vibrate to make a low buzzing sound.


The long established family name Gryllidae -- <Habits>; <Adults> & <Juveniles> -- has been used for the true crickets, but current changes in classification does not distinguish them as a clear taxonomic group (see Orthoptera Classification). They more closely resemble the long-homed grasshoppers in their antennae, ovipositor and stridulatory apparatus, and appear to be directly related to them. Gryllus domesticus, the house-cricket, competes with the cockroaches for a place in domestic dwellings and leads there a similar life. Gryllotaipa gryllotaipa, the mole cricket, is subterranean in habit. It is possible to estimate ambient temperature from the rate of their crick-crick chirps. [Also see: Gryllacrididae <Habits>; <Adults> & <Juveniles> --].


Order Blattaria


The order Blattaria are the cockroaches, sometimes called "water bugs", which have been transferred from the Orthoptera to the current 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.


Further detail on Blattaria may be found at <Blattariamed.htm>




During the 20th Century the Chlorinated Hydrocarbons were widely used to control grasshoppers in North America and Africa, where they periodically cause great damage to agricultural crops. But today the these compounds have been banned because of their carcinogentic properties. The Desert Locust, Schistocerca gregaria, of Africa has been considered as the most destructive insect in the world. It has been responsible for periodic famine. It migrates from central Africa to more northern regions where the damage cause is severe. With the ban of these insecticides in North America cultural means of control were substituted, which requires plowing the fields before springtime.


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 systems.

Key References: <medvet.ref.htm> <Hexapoda> [Additional references may be found at: MELVYL Library]



Appel, A. G. & L. M. Smith. 2003. biology and management of the smokey-brown cockroach. Ann. Vev. Entomol. 47: 33-55.

 Bell, William J. & K. G. Adiyodi. 1981. American Cockroach. Springer Verl.. p. 4. 

Bell, William J.; Roth, Louis M.; Nalepa, Christine A. 2007. Cockroaches: Ecology, Behavior & Natural History. JHU Press. pp. 5558.

Bernton, H.S. & H. Brown. 1964. "Insect Allergy Preliminary Studies of the Cockroach". J. Allergy. 35 (506513): 50613.

Bhattacharya, S. 2003. Plague of locusts causes mass allergy attack. New Scientist Mag.

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Borror, D. J., D. M. DeLong & C. A. Triplehorn. 1981. An Introduction To The Study of Insects, 5th ed. Saunders Publ., NY. 827 p.

 Brenner, R.J., P. Koehler, & R. S. Patterson. 1987. "Health Implications of Cockroach Infestations". Infestations in Med. 4 (8): 349355.

Burgess, N. R. H. & K. N. Chetwyn. 1981. Association of cockroaches with an outbreak of dysentery. Trans. Roy. Soc. Trop. Med. & Hyg. 75-332-3.

Cleveland, L.R., S. K. Hall, E. P. Sanders, & J. Collier. 1934. "The Wood-Feeding Roach Cryptocercus, IN: Protozoa, and the Symbiosis between

Protozoa & Roach". Mem. Amer. Acad. Arts & Sci. 17 (2): 185382.

Cram, E. B. 1937. A species of Orthoptera serving as intermediate host of Tetrameres americana of poultry in Puerto Rico. Proceedings of the

Ornithological Society of Washington 4: 24.

Elgerdi, R. M., K. S. Ghenghesh & N. Berbrash. 2006. Carriage by the German cockroach (Blatella germanica) of multiple antibiotic-resistant

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Fink, A., A. Permin, K-M. V. Jensen, J. Bresciani, and H. B. Magwisha. 2005. An experimental infection model for Tetrameres americana (Cram).

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Freeman, M. A. 1968. Pharmacological properties of the regurgitated crop fluid of the African migratory locust, Locusta migratoria L. Comparative

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Gordh, G. & D. H. Headrick. 2009. A Dictionary of Entomology (2nd ed.). Wallingford: CABI. p. 200.

Gore, J. C. & C. Schal. 2007. Cockroach allergen biology and mitigation in the indoor environment. Ann. Rev. Entomol. 52: 439-63.

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Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59-120

Liboreau, M. J. T. Costa & C. Rivaul. 2012. The social biology of domiciliary cockroaches: colony structure, etc. Insectes Sociaux 59(4): 445-52.

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O'Neill, K. M. 1985. Livestock Dung as a food resource & thermal refuge for rangeland grasshoppers (Orthoptera: Acrididae). Pan-Pacific

Entomologist 70: 222-229.

McKittrick, F.A. 1965. A contribution to the understanding of cockroach-termite affinities . Ann Ent. Soc. Amer. 58 (1): 1822.

Pai, H. H., W. C. Chen & C. F. Peng. 2005. Isolation of bacteria with antibiotic resistance from household cockroaches (Periplaneta americana and

Blatella germanica). Acta Tropica 93: 259-65.

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Rentz, David. 2014. A Guide to the Cockroaches of Australia. CSIRO Publishing Corp. 

Richman, Dina L. 2014. Asian cockroach. Featured Creatures. University of Florida.

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