At the moment an insect is killed, enzymes start to cut its DNA. The shorter the DNA fragments are the more difficult it will be to sequence them. The main idea of all methods aiming to preserve the DNA is to slow down or eliminate the process of DNA degradation.
The easiest way to preserve the DNA is to collect specimens directly in a vial with 96% or 100% ethanol. Ethanol will dehydrate the tissues and make the enzyme molecules defunct. As a result, the DNA will be preserved. Since live specimens contain a lot of water, they will dilute the ethanol. It is helpful to change the ethanol, a little while after the specimens have been collected. If the specimens/ethanol volume ratio in the vial is high, it may help to change ethanol more than once.
High temperature may also contribute to DNA degradation. While in the field, it may be helpful to avoid exposing samples to the sun or other sources of heat. Back in the lab, it is helpful to put the vials in the freezer (better) or a fridge.
If it is not possible to collect specimens directly in ethanol, the following guidelines should be kept in mind:
• Some chemicals commonly used in traps are not suitable for DNA preservations. They include formalin and solutions containing formalin, ethylene glycol, acetic acid and propanol.
• If specimens are collected in 70% ethanol instead of 96% or 100%, they should be transferred into high concentration ethanol as soon as possible.
• If specimens are killed using ethyl acetate or cyanide, they should be transferred to ethanol as soon as possible
• If specimens are dried very fast, and kept at low humidity (e.g., using silica gel), this may be sufficient to preserve the DNA. High humidity lets fungi and/or bacteria colonize the specimens and destroy their DNA.
• Propylene glycol, or solutions with high concentration of propylene glycol may be suitable for preserving the DNA of specimens collected by Malaise or flight intercept traps. As soon as possible the specimens should be transferred to ethanol.
It is important to mention that if specimens are kept in 96% ethanol AT ROOM TEMPERATURE, their DNA may be severely degraded within a few years.
If you have an opportunity to contribute to our projects with specimens, we can send you plastic tubes. Eppendorf-style centrifuge tubes are not the best, as the caps are often not tight enough (resulting in quick evaporation of the ethanol). We use plastic tubes with O-ring screw caps.
Last updated: April 17, 2009