Bed bugs are insects belonging to the Cimicidae family that feed by sucking blood from humans and other warm-blooded animals. Their importance to human health stems from the itching and dermatological reactions caused by their bites, as well as the psychological distress and economic losses they can inflict. The most common species affecting humans are Cimex lectularius (common bed bug), Cimex hemipterus (tropical bed bug), and Leptocimex boueti. Since the 1990s, there has been a significant resurgence in bed bug infestations worldwide.

Classification

Bed bugs belong to the order Hemiptera, infraorder Cimicomorpha. Within this infraorder, the main families of medical importance whose members are hematophagous (blood-feeding) at all stages are Cimicidae, Reduviidae (specifically the Triatominae subfamily), and Polyctenidae. The Cimicidae family comprises approximately six subfamilies, 24-25 genera, and over 100-110 species. Most of these species are associated with bats. The biogeographical distribution of the family includes genera endemic to the New World and the Old World, as well as some found in both regions.

The genus Cimex includes about 23 described species, often categorized into groups such as the C. lectularius group and the C. hemipterus group. Species that primarily feed on humans include C. lectularius, common in temperate regions, and C. hemipterus, found in tropical regions. In West Africa, Leptocimex boueti is another species that affects humans. Other Cimex species such as C. columbarius (pigeon bug), C. pipistrelli (bat bug), C. pilosellus, C. adjunctus, and C. dissimilismay also occasionally feed on humans. Additionally, there are "bird bugs" associated with birds (e.g., C. columbarius) and "bat bugs" associated with bats (e.g., the Pilosellus group and Pipistrelli group).

Morphology

Cimex lectularius is a wingless insect with a dorsoventrally flattened body. Its average length is 4-5 mm, but it can reach up to 7 mm. Unfed individuals are pale yellow-brown, while those engorged with blood take on a reddish-brown or dark brown color. Their mouthparts are of the piercing-sucking type, forming a structure called a rostrum (proboscis). Their antennae are four-segmented. A distinguishing feature is the pronotum (anterior part of the thorax): C. lectularius has broad lateral lobes, whereas C. hemipterus has a narrower pronotum. Their wings are vestigial, existing as non-functional wing pads, and they cannot fly. They also possess scent glands that produce a characteristic odor.

Life Cycle and Biology

Bed bugs undergo hemimetabolous (incomplete) metamorphosis. Their life cycle consists of an egg stage, five nymphal instars, and the adult stage. All stages, except the egg, must feed on blood. After a blood meal, females lay approximately 150-200 sticky eggs (in some cases up to 540) in secluded places. The hatching time of the eggs depends on temperature; for example, it takes 3-14 days at 23°C, while eggs do not hatch below 13°C or above 37°C. Eggs can remain viable for months at low temperatures.

Nymphs resemble adults and must take a blood meal to molt to the next stage. The development time from egg to adult is optimally 24 days at 30°C, but this period can extend to 128 days at 18°C. Bed bugs are generally active at night, feeding on their hosts. They feed on average every 3-7 days, and a blood meal takes 5-10 minutes to complete. They locate their hosts through body heat, carbon dioxide (CO2

​), and host odors. Adults can survive for more than a year without a blood meal under favorable conditions, and nymphs can survive for 5-6 months without food at low temperatures. Traumatic insemination is a characteristic mode of reproduction for the Cimicidae family. Bed bugs form aggregations using pheromones.

Evolution, Dispersion, and History

The oldest fossil of the order Hemiptera dates back approximately 310 million years. The fossil of Quasicimex eilapinastes, considered an ancestor of the Cimicidae family, is about 100 million years old. It is thought that the Cimicidae family evolved before bats, initially living on an unknown host and later colonizing bats. The lineages of C. lectularius and C. hemipterus diverged approximately 47 million years ago. The oldest Cimex fossils associated with human environments were found in the Paisley Caves in the USA, dating back 5,100 to 11,000 years.

It is estimated that the switch of bed bugs from bats or birds to humans occurred when humans began to inhabit caves in the Middle East, Europe, or India. According to ancient records, bed bugs were known in Egypt about 3500 years ago, in Greece in 400 BC, in Italy in 77 AD, in China in 600 AD, in Germany in the 11th century, in France in the 13th century, and in England in 1583. They are thought to have reached the Americas with European colonists in the 1700s.

In the mid-20th century, the use of effective insecticides like DDT led to a significant reduction in bed bug populations. However, since the 1990s, they have re-emerged globally due to increased international travel, the development of insecticide resistance, and changes in pest control practices. In Türkiye, outbreaks caused by C. lectularius have been reported, especially in student housing and dormitories in some provinces like Konya.

Epidemiology and Current Distribution

C. lectularius is a cosmopolitan species, predominant in temperate regions, and found on all continents except Antarctica. C. hemipterus is more common in tropical and subtropical regions. During the day, bed bugs hide in cracks and crevices in walls, bed frames, furniture, and mattresses. They can be found in various environments, including homes, hotels, student dormitories, and public transportation.

Their spread is usually passive, through human belongings such as luggage, clothing, and furniture. Bed bug infestations are not directly linked to poor hygiene, although clutter can provide them with more hiding places.

Importance for Human Health and Pathogenesis

Bed bug bites typically cause itchy, red welts (macules, papules), or sometimes blisters (bullae) on the skin; the severity of the reaction varies from person to person. These lesions can persist for about a week. Systemic allergic reactions are rare but can occur. Bed bug infestations can lead to psychological problems such as anxiety, insomnia, and stress. Economically, they cause control costs and losses in the tourism industry.

Over 40-50 pathogens, including Hepatitis B virus, HIV, bacteria like Borrelia recurrentis, Coxiella burnetii, Bartonella quintana, and parasites like Trypanosoma cruzi, have been isolated from bed bugs. It has been shown that T. cruzi can be transmitted experimentally by bed bugs. However, to date, there is no conclusive evidence that bed bugs effectively transmit any disease to humans under natural conditions.

Control and Management

Controlling bed bugs is challenging due to their hiding behavior, reproductive potential, and developed resistance to insecticides.

• Physical Control:
• Thorough inspection and monitoring are important.
• Vacuuming with a high-suction vacuum cleaner is beneficial.
• Washing items at high temperatures (e.g., 60°C) or freezing them (at least -17°C for 2 hours) is effective.
• Steam cleaning devices can be used.
• Heat treatment can be applied to an entire room or to items; the lethal temperature for adults is around 48.3°C, and for eggs, it is about 54.8°C.
• In cases of heavy infestation, some items may need to be discarded.
• The use of mattress and box spring encasements can help prevent spread.
• Chemical Control:
• Historically, substances like arsenic, mercury, sulfur, cyanide gas, and DDT were used. Later, organochlorines (DDT, Dieldrin), carbamates (Carbaryl, Propoxur), and organophosphates (Diazinon, Malathion) became common.
• Currently, chemicals such as synthetic pyrethroids (Permethrin, Deltamethrin, Cyfluthrin, Lambda-cyhalothrin), neonicotinoids (Imidacloprid, Acetamiprid, Thiamethoxam, Dinotefuran), and pyrroles (Chlorfenapyr) are used. These chemicals are often applied in combination.
• Application methods include spraying, dust application (which may have longer residual activity), and fumigation.
• Sulfuryl fluoride or carbon dioxide (CO₂​) (requires high concentration and long duration) can be used as fumigants. Misuse of some fumigants, like aluminum phosphide (as in a case in Konya), can have fatal consequences.
• Insect Growth Regulators (IGRs) such as methoprene and hydroprene affect nymphal stages but are slow-acting.
• Control with Natural Products:
• Natural products like diatomaceous earth (DE) and silica gel (silicon dioxide) are also used. These substances abrade the insect's cuticle, causing dehydration, and can be effective against resistant strains.
• Some essential oils, like cedar oil, have also been used.
• Biological Control:
• Entomopathogenic fungi such as Beauveria bassiana show promise as biopesticides, especially against pyrethroid-resistant bed bug strains.
• The bacterium Wolbachia has been reported to slow the growth of bed bugs.
• Resistance:
• Bed bugs have developed widespread resistance, particularly to synthetic pyrethroids. It is thought that resistance to DDT led to cross-resistance to pyrethroids.
• Resistance to neonicotinoids, carbamates, and organophosphates has also been reported.
• Resistance mechanisms include target-site insensitivity (e.g., kdr mutations in sodium channels), increased metabolic detoxification, reduced penetration, and behavioral resistance (the latter being less documented for C. lectularius)

Prevention

• When traveling, inspect hotel rooms (bed, headboard, luggage racks) for signs of bed bugs.
• Keep luggage and bags off the bed and floor; if possible, wrap them in plastic bags.
• Upon returning from a trip, unpack luggage directly in the bathroom or garage, and launder washable items at high temperatures.
• Be cautious when acquiring second-hand furniture.
• Trained dogs can be helpful in detecting bed bug infestations.