Natural history collections are an invaluable source of biological data [1–3]. These collections record the distribution of known taxa in space and time and document both what we know and what we don't know about the world's biota . Biologists all over the world have been extracting ecological, morphological, phylogenetic, diversity and biogeographic data from museum specimens for decades, if not decennia . More recently these specimens are also in frequent use for the extraction of DNA in e.g. molecular phylogenetic, population genetic and conservation genetic studies [5–9]. It could also be expected that Natural history collections will be much more important in molecular studies in the near future owing to; 1) difficulties to collect fresh biological material from many regions and the extinction of taxa due to habitat loss, and 2) the development of new high-throughput sequencing methods  and protocols that makes it possible to use these techniques for PCR-product sequencing  and conducting extensive molecular studies based on fragmented DNA in museum collections.
Museum collections are prone to attacks by insect pests, especially beetles of the family Dermestidae (Coleoptera). If left unattended these pests can completely destroy an insect collection within a few months time. Hence a variety of methods have been developed to eradicate the pest insects e.g. fumigation or other treatments with insecticides [12, 13], traps [14–16], heating [17–19] or freezing of infested specimens [20–22] and modified atmosphere [23–28].
Many different insecticides have been used in eradication of pest insects in collections. The use is declining, but it is still utilized in many museums [29, 30]. Several studies of the effects of insecticides on the pest insects e.g. [12, 31] and their effect on different materials in museum collections [32, 33] have been performed, but there are few studies of how insecticides affect the DNA of the specimens in natural history collections. Whitten et al  found no effect of sulphuryl fluoride (Vikane) on the DNA of herbarium specimens. According to Kigawa et al.  methyl bromide, ethylene oxide, propylene oxide and methyl iodide all affected the DNA in both freeze-dried mushrooms and chicken muscle negatively, whereas sulphuryl fluoride did not. To our knowledge no studies on the effects of insect DNA have been performed.
Naphthalene, paradichlorobenzene and dichlorvos are some of the most frequently used insecticides in insect collections, but their effect on the DNA of insect specimens is not known. We therefore exposed dried insects to various concentrations of these insecticides over a period of 20 months (605 days), extracted DNA from the specimens and ran both total DNA extracts and polymerase chain reaction (PCR) products on agarose gels to investigate effects of these insecticides on the DNA of insect specimens.