INTRODUCTION
Bed bugs are one of mans’ closest and longest established ectoparasites. Bed bugs have been biting us pretty much since our evolutionary origins. Evidence suggests the parasites first fed on bats, turning their attention to humans after we began inhabiting the same caves. As our species moved from caves to built structures the bed bug diverged into a distinct specie leaving the bat bug (Cimex adjunctus) to feed on the bats. Since that time, the specie has split into 2 distinct sub species. the temperate bed bug (Cimex Lectularius) and the tropical bed bug (Cimex hemipterus) and humans have subsequently carried bed bugs all over the world. Although now called bed bugs this is a greatly misleading name as they can be found in cars, busses, aircraft, bars of anywhere else people come to rest for any period of time.
IDENTIFICATION
Bed Bugs both Temperate and tropical grow to 4-7 mm in length. The males are slightly smaller than females. They are oval in shape and flattened dorsoventrally. Depending on the age and feeding condition of the bug they can appear from a light yellow to dark mahogany brown. Early instars resemble smaller versions of the adult bug.
ANATOMY
Head –
The head has 2 large compound eyes, well separated and project outwards at the sides of the head. A pair of well-developed antennae project up and consist 4 distinct segments, with last three segments being long and slender. The Mouthparts are of piercing and sucking type with 3 obvious segments bearing the piercing mandibles. The mouthpart is carried backwards under the head when not feeding and reaches as far back as the first leg.
Thorax –
The prothorax is deeply indented where the head is attached. The insect appears wingless, although they are actually micropterus due to secondary winglessness, the hind wings are absent, and the forewing reduced to form oval hemelytral pads that can be seen under magnification on the mesothorax.
Scent glands are located on the ventral surface of the metathorax.
Abdomen –
The abdomen comprises 11 segmented. When the bed bug feeds the abdomen increases in size and exposes the intersegmental membranes situated between abdominal segments 2-5
7 pairs of prominent spiracles can be clearly seen under magnification ventrolaterally on segments 2–8. These spiracles open when the insect expands the muscles in its abdomen and close when the insect contracts its abdominal muscles.
In females the rebagal pleat is present on the posterior edge of the 5th abdominal segment behind which lies the Berlese gland.
Legs –
Bed bugs have 6 legs, each with a tibial pad and two simple claws at the end. The claws allow bed bugs to cling to various rough surfaces, and on smooth surfaces, the tibial pad helps them grip. The tibial pad is considerably more developed in the tropical bed bug.
HARBOURING BEHAVIOUR
Bed bugs have a cryptic lifestyle, meaning they spend most of their time sheltering together forming congregations in cracks and crevices where they will not be seen or disturbed. They are not nocturnal but are phototoxic (they move away from light), They are most active at night, between midnight and 5:00 am. They prefer to conceal themselves close to where people sleep. Bed bugs tend to hide near where they feed but will crawl longer distances in search of a meal if necessary. Initially, they prefer to focus on beds, sofas, and other sleeping and resting areas, but they may spread elsewhere if infestations are permitted to continue, making removal more difficult.
FEEDING BEHAVIOUR
Bed bugs belong to a family of insects called Cimicidae. All members of this family feed on blood both mammalian and avian. They are most active at night, between midnight and 5:00 am. It is during this time, that their human host is typically in their deepest sleep. This behaviour reduces the risk of discovery or injury to the bed bugs during their feed. Although Bed bugs normally feed at night, they are extremely adaptable and can change their feeding period based on the host’s regular movements. In circumstances where the occupant spends much of the day sitting in one spot, chairs and sofas sometimes become infested. In such cases, during the day, bed bugs would be compelled to feed while the host is present. Bed bugs feed on exposed skin and often prefer not to climb onto the host as they feed. This can cause bites to occur in rows as they move along the edge of the exposed skin searching for a suitable feeding site. We have seen bed bugs travel long distances to reach their human host. Bed bugs are attracted to CO2 in the hosts breath, at closer range they are also attracted to body heat. However, bed bugs are only able to detect these stimuli at distances of less than 1m. Beyond this distance foraging behaviour is believed to be a random blundering until a stimulus is detected. Bed bugs can move quite quickly, and it is thought that they do a lot of wandering around before they are able to locate their food source.
Ideally when they are not feeding bed bugs would like to congregate near the host’s sleeping area, on solid structures such as divan bases and headboards. However, this is not always possible in heavy infestations or where infestations are introduced a distance from prime harbourage. Once a bed bug finds the host, they probe the skin with their mouthparts to find a blood capillary they can be seen to rear up as they move their mouthparts from under their abdomen to a forward feeding position. During probing the bug can be seen to be rocking as it searches for blood vessels at different points in the same bite hole. A bed bug may probe the skin several times before it starts to feed. Each probing is perceived as a bite by the host even though no feed is taken resulting in a disparity between the perceived and real size of an infestation. Once the bed bug locates a suitable feeding site, it will feed for 5-10 minutes. After the bed bug is full, it will leave the host and return to a crack or crevice, usually where other bed bugs are aggregating. This is not usually a tight harbourage as the bug needs to void the water content of the meal before they can fit into crevices. The bed bug will then begin digesting and excreting their meal. Bed bugs usually feed every 3-7 days, which means that a colonies feeding is staggered to further reduce the risk of discovery.
MATING BEHAVIOUR
After feeding, adult bed bugs, particularly males, are very interested in mating. Bed bugs being cimicids have unique process of mating called traumatic insemination. Unlike all other insects the male does not insert its reproductive organ into the female genitalia, it literally stabs it through her abdominal body wall at the rebaga into a specialized organ, called the Berlese gland. The sperm is released into the female’s body cavity, where over several hours it will migrate to her ovaries and fertilize her eggs. The traumatic insemination creates a wound in the female’s body that leaves a scar. The female’s body must heal from this wound and consequently, females are known to migrate away from aggregations to avoid any further injury. This post mating migration is also key in bed bugs ability to spread to new areas and to form new infestations. Studies have shown that mated females are repelled by normal aggregation pheromones during this recovery period. Females that are only mated once have been shown to lay considerably more viable eggs than bugs that are repeatedly mated. Interestingly nymphal stages of female bed bugs have fully formed scent glands it is believed that this is to prevent immature females being mated and sustaining potentially life-threatening injuries.
Why is this important?
In practical terms, this suggests that, if she has access to daily blood meals, a single mated female brought into a home will cause an infestation without having a male present. In order to fertilize her eggs, the female will eventually run out of sperm and will have to mate again.
The mating scar on the rebagal pleat enables those of us who work with bedbugs to ascertain the mating status of a female. In practical terms if we find a male or virgin female in a property it poses far lower risk than a mated female.
EGG PRODUCTION
The size and number of egg clusters a female can produce in her lifetime is regulated by her access to regular blood meals. The more meals the female can take the greater the number of eggs she will produce. The average adult female, for instance, would live for around one year. She would produce far more eggs in that year if she can feed every week than if she can only feed once a month. Due to the number of variables that control egg laying and hatching we can only take an average for comparative purposes. On average female bed bug will produce between 4- 7 eggs per day for about 10 days after a single blood meal. She will then have to feed again to produce more eggs in any significant numbers. A single female can produce about 140 eggs in her lifetime, roughly equally spread between male and female. Eggs can be laid singly or in groups. A female can lay eggs anywhere in a room. Under optimal conditions, egg fecundity is high and approximately 97% of the eggs hatch successfully. Due to the high number of eggs a single female can produce and the speed that they hatch, a bed bug population can in theory double in size every 14-21 days.
NYMPH DEVELOPMENT
The temperate bed bug has five developmental life stages. Each immature life stage is called a nymph with each nymphal stage called an instar. Each instar must take a blood meal to develop into the next life stage. Seeing as bed bugs have their skeleton (exoskeleton) on the outside of their body, as in all insects, they must shed their exoskeleton in order to grow larger. This exoskeleton shedding is called moulting. To moult effectively, a bed bug nymph must take a full blood meal. The bed bug becomes an adult after developing through five instar moults. The complete process of development from an egg to an adult will take place at ideal temperatures in about 37 days. Depending on constant access to blood meals and favourable temperatures, adult bed bugs have a life span of nearly one year. The time it takes to develop through each bed bug nymph depends on the ambient temperature and a host’s regular presence. Under optimal conditions, such as a normal indoor room temperature, within 5 days of taking a blood meal, most nymphs will progress into the next level. If a blood meal can be taken by a newly moulted instar, it will stay in that instar for 5-8 days before moulting again. However, if a bed bug nymph does not have access to a host, it will stay in that current instar until it is able to find a blood meal, or it dies. It will take approximately 37 days for a bed bug to develop from an egg, through all five nymphal instars, and into a reproductive adult. Even in the ideal circumstances, prior to becoming breeding adults, some bed bug nymphs will die. The first instars are particularly susceptible. Newly hatched nymphs are extremely small and are unable to move large distances to find a host. The first instar can die of dehydration before ever taking its first blood meal if an egg is laid too far from the host. Laboratory tests, however, have shown that overall survival of bed bug is good under favourable conditions, and that over 80% of all eggs survive to become breeding adults.
The latest findings suggest that a well-fed adult bed bug kept at room temperature can live in the laboratory for between 99 and 300 days. Unfortunately, under field conditions, we do not know exactly how long a bed bug could live. However, for bed bugs living in human living environments, conditions are typically more difficult than they are in the laboratory. Food supply, temperature and humidity variations, the presence of insecticides, the risks of being crushed, environmental disturbances can all have a detrimental effect on the survival of the bed bug. A recent experimental study has shown that starvation has a detrimental effect on the survival of bed bugs. This modern research contradicts European studies conducted in the 1930s and 40s, when it was found that bed bugs could survive hunger cycles of more than a year.
Although this may have been accurate for individual bed bugs living at very low temperatures, this most recent study states that modern bed bugs collected in the United States from homes do not survive that long. On average, starved bed bugs kept at room temperature will die within 70 days. These bed bugs are most likely to die of dehydration, instead of starving to death. Dehydration is the greatest natural threat to their survival while living in the indoor climate since bed bugs have no source of hydration other than their blood meal. In fact, one of the reasons why bed bugs pack themselves so tightly into tiny cracks and crevices is that they can maintain a favourable temperature and humidity microhabitat, thereby increasing their ability to withstand hunger cycles.
FAECAL SPOTS
After they have eaten, bed bugs begin to produce dark, aqueous faecal material. One of the first signs of an infestation is always these faecal spots. One of the most recognizable tell-tale signs of bed bugs are black, ink-like stains on the sheets, mattress, or bed frame. However, spiders, flies and German cockroaches can create very similar spots, so location can be an important factor in separating the two. Blood identification kits such as luminol and presumptive assay kits have shown that the faecal content of blood-feeding insects, such as bed bugs, can be differentiated from that of other household invertebrates.
Based on the relative proportions of digested blood and uric acid, faecal spots can differ in colour from black to tan. The presentation of the faecal spots is also affected by the absorption of the substrate on which they are placed. Faecal spots become wicked into the fabrics, resembling ink from a fountain pen, when deposited on absorbent surfaces such as bed sheets. Faecal spots, often dry as a dark, raised lump, when deposited on non-absorbent surfaces, such as varnished wood.
BITES
Symptoms vary from person to person after being bitten by bed bugs. Within a day or so of the bite, many grow an itchy red welt. Others do not or have no reaction. The reaction is often delayed for days or even weeks particularly if it is the first time that the sufferer has been bitten, which can make it hard to know where or when bites occur. Studies conducted in bed bug-infested apartments show that even when bitten repeatedly, about 30 percent of people do not respond, and even higher levels of non-reactivity occur among the elderly. More serious (anaphylactic-like) systemic reactions are rare but have been reported. With bed bugs being a blood feeding insect, a common concern is whether they are transmitting diseases. While different pathogens may be found in bugs, transmission to humans has not been proved and is considered unlikely. Itching and inflammation from their bites are the key medical concerns. For the prevention of infection antiseptic or antibiotic ointments can be prescribed. To minimize allergic reactions, and discomfort antihistamines and corticosteroids can be applied. While bed bugs are not known to transmit diseases, they may decrease the quality of life by causing discomfort, insomnia, anxiety, and embarrassment. According to some health experts, the added stress from living with bed bugs can have a significant impact on the emotional health and well-being of certain individuals.
