A study on how bed bugs can survive genetic inbreeding was presented at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH). The study offers new insights into the rapidly growing problem of bed bugs across the U.S. and worldwide. In the U.S., in the 1950s the common bed bug (Cimex lectularius) almost entirely disappeared. However, over the past decade they have made an enormous comeback. These stubborn blood-sucking bugs have developed a resistance to the insecticides (pyrethroids), which used to be extremely effective in controlling them.
In addition, the researchers at ASTMA offered to ways to control infestations in homes and apartment buildings: including new information on chemical compounds involved in attracting and repelling these insects, as well as a new method for preventing resistance to insecticide.
Although bed bugs do not transmit disease, their bites trigger allergic reactions, such as severe itching and inflamed welts (red bump, ridge or swelling of unbroken skin). These parasites pose both a social and economic hazzard to owners and residents of apartment buildings, as well as hotels and public buildings. The financial impact of bed bug control has been significant.
Rajeev Vaidyanathan, PhD, associate director of Vector Biology and Zoonotic Disease at SRI International, explained:
“New York City alone spends between $10 million and $40 million per year on bed bug control, and these numbers are repeated in other major cities across the US. Over 95 percent of pest control agencies reported bed bugs as a priority in 2010, thus superseding termites as the number one urban pest.”
In hotel rooms, single family homes, and multi-unit housing, the number of reported infestations has risen 10 to 100 times more than the number of reports recorded in 1990. Nobody is completely sure why there has been such an explosion in reported occurrences.
One factor that seems to contribute to their effective infestation is their ability to produce healthy young through inbreeding, meaning only a few bed bugs are needed to produce infestations.
Coby Schal, PhD, and Ed Vargo, PhD, both entomologists at North Carolina State University (NCSU), and colleagues conducted two investigations currently under peer-review that analyzed the genetics of these pests from three multi-story apartment buildings in New Jersey and North Carolina. The researchers found in each apartment there were high levels of inbreeding, and that genetic diversity was very low, suggesting that only one or two bed bugs are needed in order for an infestation to occur. The ability to be able to produce healthy offspring through inbreeding allows these bugs to expand the infestation to other apartments within the building without any outside help.
This same conclusion was reached in another study carried out by Schal and Vargo, who examined 21 infestations from Maine to Florida – in almost all of the infestations, just a single room within the home was found to be the source.
“Inbreeding gives bed bugs an advantage in being able to colonize. A single female that has been mated is able to colonize and start a new infestation. Her progeny and brothers and sisters can then mate with each other, exponentially expanding the population. With many organisms, extensive inbreeding would cause serious mutations that would eventually bring about an end to the population.”
Schal adds that cockroach’s also have the ability to survive inbreeding too.
According to latest research, bed bugs have become increasingly resistant to insecticides that had previously been effective. The study demonstrates that it is possible to “shut down” the mechanism that eventually leads to resistance to pyrethroid insecticides.
Ken Haynes, PhD, and team at the University of Kentucky have focused on bed bug resistance to insecticide for the last five years. The team, which included Subba Reddy Palli and Fang Zhu, decided to target specific enzymes within the pests that are connected with the P450 detoxification systems that break down the insecticides before they reach their molecular target in order to find a method that could eliminate resistance. Instead of trying to eliminate all the enzymes in the system, they used RNA interference against an enzymatic partner of the P450 family in order to turn off selective systems inside the bugs, and preserve the utility of deltamethrin (insecticide).
According to the researchers if they are able to understand and identify the function of chemical compounds secreted by the bed bugs they may be able to discover addition options for controlling bed bug populations. At present the team discovering novel compounds that influence the behavior of bed bugs. Recently, Vaidyanathan’s team were able to isolated 7 new compounds that had never been identified from bed bugs that may serve as bed bug attractants. The team explained that it may be possible to create a trap with a “cocktail” of these compounds in order to attract the bed bugs.
Mark Feldlaufer, PhD, an entomologist with the US Department of Agriculture’s Agricultural Research Service, is investigation further the underlying mechanisms of the chemical factors, or pheromones that influence the behavior of bed bugs. Feldlaufer has analyzed the chemical layout of “alarm compounds,” which lets animals of the same species know danger is present. These alarm compounds could be used as “dispersants” during a chemical treatment, thereby exposing more pests to the treatment.
Furthermore, Feldlaufer’s investigation has discovered the chemicals connected with the outer skeleton of bed bugs. Feldlaufer’s is not focusing if there is any role of these chemicals in the ability of dogs to sniff out these pests. Pest control experts use dogs that are properly trained and handled in order to find bed bugs just as dogs are used to find explosives, drugs or lost individuals.
Vaidyanathan, explains “Bed bugs are our oldest roommates. There is even evidence of bed bugs in Pharaonic Egypt.”
The researchers state that numbers factors have contributed to the most recent resurgence of bed bugs in the U.S..
“The problems we are seeing with bed bugs in North America did not happen overnight. They are the consequence of multiple repeated introductions from all over the world. We have the highest concentration in the history of our species of humans living in cities. For as long as we’ve been standing on two legs, we’ve lived in rural areas. Over the last ten years, the majority of humans have moved to urban areas. This is the perfect setting for creating a high density of mammal nests for bed bugs. Bed bugs do not have wings; they are nest parasites, so our own population density has helped them to thrive.”
Although low genetic diversity within individual infestations was observed, the NCSU team discovered that along the East cost there is a high genetic diversity across infestations as the bed bugs are most likely coming from abroad of several other different places within the US.
Prior investigations verify that one of the biggest indicators for the presence of these pests is turnover of residents. In addition one of the primary factors powering infestations is the increase in domestic and international travel.
According to Vaidyanathan bed bugs feed on chickens, and industrial production of poultry offers the optimal breeding ground for bed bugs. However, the team also state that increased introduction of second hand furniture in household items into homes also contributes to the spread.
At present, heat treatments or insecticide are used in order to control these infestations. The team highlight that insecticides readily available to the general public have generally not be tested against bed bugs. Heat treatment involves heating the entire home, or heating all furniture and belonging in a box at a high temperature for 1 hour, however both insecticides and heat treatments are costly and are not optimal for chronic infestations. The team call for enhanced education, improving current techniques for detection, as well as safe and more effective control methods.
Peter J. Hotez, MD, PhD, president of ASTMH, said:
“Just as with other global diseases once thought under control and then neglected, bed bugs have shown the ability to resurge in great numbers once our vigilance wanes. To stay one step ahead of bed bugs and other parasitic organisms, we need to sustain investment in research for new tools.”
Written by: Petra Rattue