Bed Bug Problems in Denmark, with a European Perspective
  Key Words  
  Cimex lectularius, resurgence, pyrethroids, organophosphates
  Ole Kilpinen, Karl-martin Vagn Jensen, and Michael Kristensen
  Based on historical data on the number of inquiries to the advisory service at the Danish Pest Infestation Laboratory we have tried to analyse the variation in bed bug infestations in Denmark since the 1950s. The bed bug problems in Denmark have gone from low levels in the 1950s, gradually increasing to a peak in the mid-1980s. From there on the problems diminished, but were still present. In the last 10 years the problems are increasing again. The available information from other European countries seems to indicate that this is the same situation in many countries. One possible reason for the recent increase in the bed bug problems is resistance against the available insecticides. To investigate this possibility we collected bed bugs from 20 different locations in Denmark and tested their sensitivity against chlorpyrifos, permethrin and deltamethrin; the most important insecticides registered in Denmark for bed bug control. Compared with a sensitive US strain there was widespread resistance against permethrin and deltamethrin whereas only cases of reduced sensitivity to chlorpyrifos were found. The resistance to pyrethroids is comparable with recent results from the US and UK, indicating that it might be found also in many other countries. This means that the pyrethroids are not a good solution for controlling bed bugs whereas chlorpyrifos continues to be active. However, chlorpyrifos will probably not be available for Danish pest control operators anymore, leaving no effective insecticides for the treatment of bed bug infestations. Therefore, there is an urgent need for the development and registration of new control methods.