With the widespread use of DDT in the 1940's and 1950's, bedbugs mostly disappeared from the developed world in the mid-20th century, though infestations remained common in many other parts of the world. Rebounding populations present a challenge because of developed resistance to various pesticides including DDT, and organophosphates. Bed bug populations in Arkansas have been found to be highly resistant to DDT, with an LD50 of more than 100,000 PPM DDT was seen to make bedbugs more active in studies done in Africa.
Because some bedbug populations have developed a resistance to pyrethroid insecticides, there is growing interest in both synthetic pyrethroid and pyrrole insecticide chlorfenapyr; insect growth regulators such as hydroprene (Gentrol) are sometimes used.
Tests show that the carbamate insecticide propoxur is highly toxic to bedbugs, but the Environmental Protection Agency (EPA) has been reluctant to approve such an indoor use because of its potential toxicity to children after chronic exposure.
Bedbug cases have been on the rise across the world since the mid-1990s. Figures from one London borough show reported bedbug infestations doubling each year from 1995 to 2001. There is also evidence of a previous cycle of bedbug infestations in the U.K. in the mid-1980s. The U.S. National Pest Management Association reported a 71% increase in bedbug calls between 2000 and 2005. The Steritech Group, a pest-management company based in Charlotte, North Carolina, claimed that 25% of the 700 hotels they surveyed between 2002 and 2006 needed bedbug treatment. The resurgence led the United States Environmental Protection Agency to hold a National Bed Bug Summit in 2009.
The cause of this resurgence is still uncertain, but it is thought to be related to increased international travel, the use of new pest-control methods that do not affect bedbugs, and increasing pesticide resistance.
One recent theory about bedbug reappearance is that they never truly disappeared from the United States, but may have been forced to alternative hosts. Consistent with this is the finding the bedbug DNA shows no evidence of an evolutionary bottleneck. Furthermore, investigators have found high populations of bed bugs at poultry facilities in Arkansas. Poultry workers at these facilities may be spreading bedbugs, unknowingly carrying them to their places of residence and elsewhere after leaving work.
Blood-fed Cimex lectularius (Note the differences in color with respect to digestion of blood meal)Bedbug pesticide-resistance appears to be increasing dramatically. Bedbug populations sampled across the U.S. showed a tolerance for pyrethroids several thousands of times greater than laboratory bedbugs. New York City bed bugs have been found to be 264 times more resistant to deltamethrin than Florida bedbugs due to nerve cell mutations. Another problem with current insecticide use is that the broad-spectrum insecticide sprays for cockroaches and ants that are no longer used had a collateral impact on bedbug infestations. Recently, a switch has been made to bait insecticides that have proven effective against cockroaches but have allowed bedbugs to escape the indirect treatment.