An Introduction to Medical Entomology
For educational purposes.
Arthropoda - Insecta
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Included in the family Cimicidae are two common species that feed on humans. Cimex lectularius occurs in both tropical and non-tropical areas, whereas Cimex hemipterus is not as common in the Americas. Service (2008) noted that the distinction between these two species is difficult, but usually the prothorax of C. lectularius is 2 1/2 times as wide as long, while in C. hemipterus it is narrower or about two times as wide as long. The abdomen of C. lectularius is also more rounded. Other geographically restricted species are, Leptocimex boueti in western Africa.), and Cimex pilosellus Horvath, C. pipistrelli (Jenyns), Oeciacus spp., Cimexopsis nyctalis List and Haematosiphon inodorus (Duges) at other world sites.
Bedbug adults are wingless and flattened dorsoventrally. Their size averages about 5-7 mm long. The head is short and broad and has a pair of prominent compound eyes in front of which is a pair of 4-segmented antennae. The proboscis is thin and usually held close to the body underneath the head and prothorax. The prothorax is larger than the meso and metathorax, and possesses winged expansions. Hemelytra are present, which have no function. Legs are well developed and slender.
Eight abdominal segments are visible even though there are eleven. The male abdomen is more pointed than the female. Service (2008) noted that females have a small incision ventrally on the fourth abdominal segment, which opens into a pouch called the mesospermalege or the Berlese Organ. It is used to store sperm after mating. Both sexes draw blood from their hosts.
Bedbugs draw blood from their hosts primarily at night, but if stressed will do so also during daytime. The bugs usually retreat to hiding places when they are finished feeding, and thus do not often remain in contact with people. Their hosts include rodents, bats and birds when humans are unavailable. Both adults and nymphs are inactive during daytime hiding in dry cracks, furniture ceilings, wallpaper, mattresses, etc. They resume activity at night but will return to hiding places after blood meals.
Bizarre indeed is the mating procedure among the Cimicidae, which was explained by Service (2008). Males penetrate the integument to incorporate spermatozoa in a "Berlese Organ" that is located on the female's ventral part of the abdomen. Subsequently the spermatozoa pass into the haemocoel (body cavity) from which they gain access to the oviducts and eggs.
The female lays three or less eggs per day in building crevices and furniture if the temperature is above 13 deg. Centigrade. The 1-mm. long eggs are white or tan, slightly curved and covered with a mosaic pattern. Female longevity varies from a few weeks to months and even years. They can lay up to 500 eggs in a lifetime. Hatching depends on temperature but vries from eight to eleven days. Eggs that have not hatched may survive for three months. Hatching produces the nymphs, which like lice resemble the adults. In this hemimetabolous cycle there are five nymphal stages, each being able to draw blood. The duration of the nymphal stages varies from two to seven weeks but again may be longer at lower temperatures.
Living bedbugs are easily detected as well as by the casts left by the nymphs during moults. Wherever they roam they leave tiny dark colored marks, such as on the beds and walls. There is also an undesirable odor in dwellings where there are high infestations. They tend to remain in single dwellings without much dispersal. Spread is frequently with infested furniture.
Hepatitis and other pathogens have been recorded in bedbugs (Mayans et al. 1994), but vectoring infections to humans is not substantiated (Service 2008). However, their presence causes distress even though there are few reactions from their feeding activity. Because they draw blood high infestations can result in iron deficiency in some young and older people especially.
Repellents and the use of pyrethrum coils afford protection, but insecticidal sprays are required for structures and furniture in case of heavier infestations. Service (2008) also noted that insect growth regulators have sometimes been used for control.
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