Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance/Bloodsucking bugs

Assassin-bugs or Conenose-bugs, and Bed-bugs (Hemiptera, Reduviidae)
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Characters of reduviid blood-sucking bugs
The term bug is used by entomologists in a formal sense for this group of insects. This term derives from ancient familiarity with Bed-bugs, which are insects highly adapted to parasitize humans. Both Assassin-bugs and Bed-bugs are nidicolous, adapted to living in nest or housing of their host. They feed at night, crawling from their hiding places in the housing of their hosts. The bugs feed fully on their hosts then return to their resting sites within the house or nest. This is especially important for the medical aspects of these blood-suckers that are well adapted to go through their entire life-cycle within the structures of poor quality housing.
 * Photograph above shows an Assassin-bug of the genus Triatoma, with its two pairs of wings folded over a wide, flat, abdomen; and its elongated head and antennae.

Both sexes feed on blood and are similar in appearance. The proboscis (or rostrum) of hemipteran bugs is long and slender; it folds away under the head when not in use. The size of the blood meals is large relative to the size of the bugs. All hemipteran bugs have an incomplete metamorphosis, with five nymph stages. Nymphs have no wings, these are gained with the final molt into an adult. Adult Assassin-bugs have two pairs of wings. When not in use the wings are folded down closely to the dorsal surface of the abdomen. The Bed-bugs are without wings at all stages.

There are many genera and species of Assassin-bugs in the sub-family Triatominae; the genera most important to health are Triatoma, Rhodnius, and Panstrongylus. One example genus is provided here.

Glossary

 * Bug = Formal name for insects within the family Reduviidae, as in Bed-bug.
 * Integument = The outer body wall of insects and acarines, which also acts as their external skeleton.
 * Nidicolous = In this context, the behaviour of insects or acarines that inhabit the nests of their hosts, compare with mites of bird nests.
 * Ocelli = A type of simple eye with a single sensory unit, in contrast to compound eyes with many sensory units.
 * Proboscis = A term (also known as rostrum) used to describe mouthparts of insects adapted for piercing or probing to feed.

Triatoma (Reduviidae)
Characters: adult, dorsal and lateral. 1- Antennae consist of 4 elongated thin segments. 2- Base of antenna is at a position midway between eyes and anterior margin of the head. 3- At the base of the head is a pair of small eyes and a pair of large ocelli. 4- Thorax has a rough texture with large tubercles; it is dark brown. 5- Pronotum of the thorax is wide. 6- Scutellum of the thorax is elongated and turned down at its posterior margin. 7- Two pairs of wings are borne on the thorax; the fore-wings have thick veins; wings at rest are folded closely over the abdomen. 8- Abdomen is wide, with a distinct rim, and in unfed bugs is flattened. 9- Abdomen has varied patterns of brown on a yellow or orange background. 10- Proboscis is very long; when not in use it is folded beneath the head.

Hosts: A wide variety of animals are used for temporary blood-feeding by Triatoma: dogs, cats, cattle, sheep, goats, poultry birds, and humans.

Signs and disease: The bites leads to irritation, wheals and erythematous papules at feeding sites. Feeding may be associated with transmission of the protozoan Trypanosoma cruzi, the causative organism of Chaga's disease of much importance to humans, and also causing similar disease in dogs. However, the transmission route is via the bug's feces containing T. cruzi which then contaminate the blood-feeding site.

Distribution: Most species of Assassin-bugs occur in tropical and sub-tropical regions of the Americas but some occur in South East Asia and Africa.

Cimex (Cimicidae)
Characters. female, ventral. 1- Adults (and nymphs) have no wings. 2- Antennae are long, with 4 segments. 3- Proboscis is long and folds under head when no in use. 4- Body is flattened dorso-ventrally. 5- Legs are well developed, each ending in paired claws. 6- Integument is densely covered with short, stout, setae.

Hosts: Humans and chickens are the principal hosts. The Bed-bugs have adapted to be closely associated with the housing constructed by humans for themselves and their poultry birds. The bugs live in cracks and crevices in both the structure of the buildings and also furniture and fittings such as mattresses.

Symptoms and disease: In contast to the Assassin-bugs, the Bed-bugs are not important as transmitters of pathogens to humans. Although the bites of Bed-bugs are often not felt by sleeping humans, the feeding site becomes inflamed, thickened and painful later on. Individual humans vary in their immune reactions to bites of Bed-bugs: some can become desensitized by repeated exposure whilst others become hypersensitized. Sometimes massive infestations build up in housing, leading to psychological distress and malaise of the inhabitants. The bugs secrete a pheromone (a chemical signal between them) which at high concentrations gives a characteristic smell perceptible to people.

Distribution: The species Cimex hemipterus is the Tropical Bed-bug; Cimex lectularius is the Common Bed-bug of temperate climates; Leptocimex boueti is a Bed-bug of importance in Africa.

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