They bite and it itches. They suck your blood and then hide in a dark corner for a couple of days to digest their bloody meal. We are talking about bedbugs. Part and parcel of the Danes’ increasing wanderlust to exotic countries is an expected increase in the frequency of bedbugs in Denmark, brought home as undesired souvenirs. Unfortunately, it seems that the little critters are not that easy to suppress.

Bedbugs can be controlled using insecticides as long as the bugs are not resistant to them. Scientists from the Faculty of Agricultural Sciences at the University of Aarhus have investigated just how resistant to the commonly used insecticides bedbugs found in Denmark actually are. The results of their studies have been published in a report from the Danish Environmental Protection Agency.

The findings are that bedbugs are resistant to several products and the product which still has a positive effect is not expected to be available in the future.

Bedbugs were collected from 20 different localities in Denmark. The small bloodsuckers were tested for resistance to pyrethroids and organophosphates. These are the two groups of insecticides that are permitted for use against bedbugs in Denmark.

Widespread resistance to the synthetic pyrethroids permethrin and deltamethrin was found. There was, however, only a slightly decreased susceptibility to the organophosphate chlorpyriphos and this product was proven to be fully effective when the bedbugs were exposed to surfaces treated with the commercial products. Since the licence for chlorpyriphos will most likely not be renewed, all that is left are the pyrethroids which the investigation showed have no effect in several of the localities tested.

For more information please contact: Head of research unit Karl-Martin Vagn Jensen, Department of Integrated Pest Management, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 3941, e-mail: Karl-MartinV.Jensen@agrsci.dk