Cimicidae

Cimicids are characterized by a short head that is broadly attached to the prothorax, an oval body, and well-developed eyes. Adults are 3-13 mm long and 3-5 mm broad, yellowish brown to reddish brown, and their body is somewhatflattened. They are wingless, but have small wing pads. Antennae are four-segmented, and the three-segmented proboscis rests in a groove beneath the head and thorax. Nymphs and adult males and females are obligate feeders on vertebrate blood. They are temporary ectoparasites on bats, birds that roost together in small to large numbers, and people. Included in this family are the bed bugs, swallow bug, pigeon bug, and poultry bug. These insects live in cracks and crevices separately from their hosts, and move to the host for periodic blood meals. Large populations ofcimicids develop when conditions and suitable hosts are available. These bugs are distributed worldwide, but mostly in the tropics and subtropics. Bed bugs have been closely associated with humans for centuries, and are nearly dependent on humans to survive. Prehistoric human communities encountered these insects in caves, and here their adaptation to feeding on humans probably occurred.

Cimicidae includes 91 described species. Mostare associated with birds or bats, but the two bed bug species, Cimex lectular-ius and C. hemipterus, are associated with humans. Although one population of C. lectularius has been found with cave bats in Afghanistan, this species is considered one of the few insects associated only with humans. It is distributed in North America, Europe, and Russia. C. hemipterus, the tropical bed bug, is common in tropical regions of Asia, Africa, and Central America where it attacks humans and chickens, and rarely bats. In general, C. lectularius occurs in temperate regions and C. hemipterus in tropical regions, but there is some hybridization, and in some regions, such as Brazil, populations of C. lectularius are increasing.

Haematosiphon inodorus occurs in Central America and Ornithocoris toledoi in Brazil. C. pipistrelli is associated with birds in Europe and C. columbarius occurs in poultry houses and pigeon cotes. Oeciacus hirundinis infests martin nests; it sometimes bites humans when adults and nymphs move inside houses when nests are abandoned. Hesperocimex sonorensis is an ectoparasite of purple martins (Proge subis) in southwestern USA and northern Mexico. Leptocimex boueti is associated with bats in West Africa, but has also been reported biting people in native huts. Other bat bugs include Stricticimex parvus, which also feeds on humans in bat-caves in Thailand.

Cimex spp. takes a large blood meal in a short time, and this behavior permits them to feed infrequently. Bed bug adults can engorge in about 5 min and take up to 1.8-24 Mg of blood per second. The blood meal weighs from 3.7 (first-stage nymph) to 4.9 (fifth-stage nymph) times the body weight of the unfed insect. Molting and egg production require a blood meal, so feeding is directly linked to development. In spite of their blood-feeding habits, cimicids are not vectors of any disease pathogens, although there is a report of their vectoring hepatitis B virus in Senegal. Investigations showed that the human immunodeficiency virus (HIV) was retained in the tropical bed bug, Cimex hemipterus, for a week. However, the virus did not replicate, was not detected in excreta, and was not transmitted to other animals after feeding.

Mating behavior is not elaborate in these bugs and the process of insemination is considered as traumatic. The female bed bug has no functional genital opening, but there is a site between abdominal segments 5 and 6 thatis modified to accept the reproductive organ of the male. The male has a C-shaped intromittant organ that curves around the tip of the abdomen, and directed to the left. This organ punctures the abdominal cuticle of the female at the modified site on the abdomen. In copulation, the male mounts the female, and curls his abdomen over the right side ofhers, and inserts his intromit-tant organ into the copulatory pore in the female's abdomen. This pore leads to a bag-like organ called the mesospermalege or the organ of Berlese or Ribaga, which serves to collect and store sperm. The sperms bore their way through the bag and migrate through the body cavity to the oviducts. They enter and fertilize the eggs, and the eggs pass normally down the oviduct. The wound created by the male during mating quickly heals and leaves a scar.

Eastern bat bug, Cimex adjunctus Adults are about 6 mm long and oval; the body is brown to dark brown. This species is morphologically similar to other Cimex spp. It occurs throughout eastern and midwestern regions of the USA. Large infestations may occur with bat populations in the attics of buildings. Adults are known to move from household harborages near roosting bats to occupied rooms and bite people during the night.

Pigeon bug, Cimex columbarius This species is morphologically similar and closely related to C. lectularius. Itis primarily distinguished by the ratio between head width and antennal segment 3: in C. lectularius the ratio is 1.45, and in C. columbarius itis 1.78. Hybridization occurs between these two species, but the offspring have low fertility. C. columbarius occurs in Europe and feeds primarily on domestic pigeons, butalso feeds on the pied flycatcher (Muscicapa atricapilla) in birdhouses.

Tropical bed bug, Cimex hemipterus (Fig. 8.2b) Adults are about 5 mm long, oval, and somewhat flattened. The apical margins of the wingpads are distinctly rounded. These bugs are reddish brown to light red depending on recent blood-feeding. The pronotum has the anterior margin moderately concave (it is deeply curved in C. lectularius); the sides of the pronotum are not dilated, and are fringed with sparse and nearly straight setae. Females lay 2-3 eggs per day; fecundity is 78-125 eggs. Hatching occurs in about 3 days. Development from egg to adult takes about 20 days: first instar lasts about4 days, second and third instar about3 days, fourth about4 days, and the fifth instar lasts about 6 days. Adult females live about 41 days and males about 198 days.

C. hemipterus and C. lectularius are closely related and hybridization between the two occurs. However, female C. lectularius mated with a male C. hemipterus die, perhaps as a result of the traumatic insemination by the male genital clasper puncturing the female abdomen. When the male C. lectularius mates with a C. hemipterus female the results are not harmful.

Bed bug, Cimex lectularius (Fig. 8.2a, c, d) Adults are 4-6 mm long, oval, and somewhat flattened; the wingpads are small. These bugs are dark brown to reddish brown depending on whether they have taken a blood meal recently. The pronotum has the anterior margin deeply concave (itis moderately curved in C. hemipterus). The body is covered with microscopic setae, which give the abdomen a slightly banded appearance. Nymphs are morphologically similar to the adults; the small wingpads appear at the last larval molt. The abdomen cuticle of nymphs is relatively thin and displays the color of the partly digested blood inside. The cuticle of the adult is thick and dark brown.

Figure Cimex
Figure 8.2 Hemiptera: Cimicidae. (a) Cimex lectularius male; (b) C. hemipterus, head and prothorax; (c) C. lectularius nymph; (d) C. lectularius female.

Eggs are about 1 mm long, yellowish white, and with a distinct cap at one end. Females deposit eggs in batches of 10-50; fecundity is about350, butranges from 200 to 500. Maximum egg-laying occurs between 21 and 28 °C; eggs do not hatch above 37 °C or below 13 °C. Hatching is in 6-17 days at 21 °C, and in 30-40 days at 14 °C. A transparent substance attaches the eggs to the substrate, and the empty chorion remains on the substrate after hatching. Development from egg to adult is through five nymph instars, and takes 14 days at 28 °C, and 118 daysati5 °C; developmentmay be further extended in unfavorable conditions. The lowest temperature at which bed bugs complete development is 13 °C. Nymphs can survive long periods without feeding: the first instar can live 114 days without a blood meal; second instar, i7i days; third instar, 2i4 days; fourth instar, 234 days; and, the fifth instar can survive 161 days. With frequent opportunity to feed, adults live about 360 days at 18-20 °C, 105 days at 27 °C, and about 70 days at 34 °C. Adult males live for about 176 days and females about 277 days without feeding. At 7 °C and 90% RH, unmated and unfed females live for 550 days, but at 23 °C and 90% RH they survive for 181 days. Under favorable conditions, there are three or four generations per year, but in unheated rooms in north temperate climates, there is one generation per year.

A blood meal is required between each molt, and before egg development. Adults do not seek food at temperatures below 9 °C; between molts they will feed in about 6 days at 15 °C to 24 h at 25 °C. Bed bugs prefer harborages with rough surfaces, and if not available in the bedstead or mattress they will find suitable sites along baseboards close to the bed, and move from these to the host. Feeding is nocturnal and usually peaks soon after sunset and before dawn, but they will feed during the day if conditions are favorable. In cool weather, the adults and nymphs may remain active in the harborage for 2-4 weeks. Carbon dioxide and warmth are the environmental features used in their host-finding behavior. These bugs will respond to temperature gradients only 2° above normal. Adults produce an aggregation pheromone and an alarm pheromone. When alarmed, bed bugs can move away at 2 cm/s, and typically emit an odor. Heavily infested sites are often characterized by a distinct odor attributed to the scent glands of adults, and accumulations of nymph and adult bug excrement in harborages. Bed bug odor is a complex mixture of chemicals, but mainly hexanol and octenol. They frequently defecate brownish-black deposits of partly digested blood in the harborage. The odor of a bed bug infestation is similar to the aroma of the spice coriander, which is a name derived from koris, the Greek word for bug. C. lectularius (cimex, Latin for bug; lectul, Latin for bed) is a common household pest in most parts of the world. Populations and pest status frequently fluctuate, perhaps depending on living conditions and the increased movement of people around the world.

Heat and cold influence bed bug development and survival. Adults are killed by exposure to —17 °C for 2 h or —18 °C for 1 h. Recently fed bugs are more susceptible to temperature extremes than partially starved ones. Exposure for 2 hat —15 °C is lethal to about 75% of eggs. At —9 °C eggs die in 30-60 days. The thermal death point for adults is 1 h at 44 °C and 24 h at 40 °C; eggs are killed at about the same temperatures.

There is little evidence thatbed bugs are vectors ofany human pathogen, but experimentally they can be infected with hepatitis B, HIV, and may be the agentfor Chagas disease, Trypanosoma cruzi.Daily feeding oflarge numbers of bed bugs can contribute to anemia in infants. Domestic infestations thatremain for long periods can be distressing, and bites can become infected after scratching. Allergic reactions to the bites are common. In some situations, C. lectularius has been found as an ectoparasite and remaining in clothing ofvagrants.

Western bat bug, Cimex pilosellus This species is distinguished from C. lectularius by long setae on the body of the adult and large nymphs, and the thorax, which extends forward on both sides of the head. It does not feed on humans, but bugs from infestations associated with bats may spread to occupied rooms in houses. This species occurs in western Canada and in western USA.

Poultry bug, Haematosiphon inodorus This species has long legs, and a long beak that extends to the hind coxae. It is sometimes called the Mexican chicken bug. It is a parasite in the roosts of birds, including owls, eagles, condors, and chickens. However, it has been reported to spread from roosts to dwelling spaces where it may bite people. The species is distributed in western and southwestern USA and Central America.

Swallow bugs, Oeciacus hirundinis, O. vicarius Adults are about 5mmlongandbrownto reddish brown; the body has numerous long setae. The middle coxae are widely separated and the beak does not extend to coxa 2. Antennal segments 3 and 4 are equal or nearly equal in length. These two species feed on swallows and occasionally attack humans. O. hirundinis occurs throughout western and central Europe, and south into North Africa. O. vicarius occurs in western North America and occasionally in some eastern states and eastern Canadian provinces. It is not associated with swallows in their South American wintering quarters. O. vicarius will also feed on the house martin, and some other bird species.

O. vicarius assemble in the empty nests of swallows in the spring (April). When migrating swallows return to the nests from their wintering quarters, the bugs take blood meals. Sometimes while feeding they are carried to other (new) nests on the body of birds. Eggs are deposited within 24 h of feeding. Eggs are laid singly or in small batches of about 16 eggs; hatching occurs in 3-5 days. Development from egg to adult takes about 60 days. They overwinter as nymphs or adults. These bugs are most active when the host birds are nesting, but show a peak of activity after the birds leave the nest site. For about 9 months of the year, swallows are absent from the nest site and the bugs have limited access to food. Some find alternative hosts, such as other birds or bats, but most species survive on food reserves in their body. However, many do not survive the winter without food. O. vicarius adults and nymphs enter houses from nests built near or on houses; in the absence of other hosts, they bite humans. Large numbers of these bugs enter houses, schools, and commercial buildings in response to the removal ofbird nests.

O. hirundinis usually feeds on other bird species, as well as mammalian hosts, than swallows. In Europe, there are two generations per year. In spring, when martins return to nesting sites, there is a peak in the bug population, primarily from those that overwintered at the nest site. In winter, there is a peak in the nymph population. Although the martins have left the nest site by then, there are other birds, such as house sparrows, that serve as hosts.

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