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Traditionally, insects collected for scientific purposes have been dried and pinned,
or preserved in 70% ethanol. Both methods preserve taxonomically informative
exoskeletal structures well but are suboptimal for preserving DNA for molecular
biology. Highly concentrated ethanol (95-100%), preferred as a DNA preservative, has
generally been assumed to make specimens brittle and prone to breaking. However,
systematic studies on the correlation between ethanol concentration and specimen
preservation are lacking. Here, we tested how preservative ethanol concentration in
combination with different sample handling regimes affect the integrity of seven insect
species representing four orders, and differing substantially in the level of sclerotization.
After preservation and treatments (various levels of disturbance), we counted the
number of appendages (legs, wings, antennae, or heads) that each specimen had lost.
Additionally, we assessed the preservation ofDNAafter long-term storage by comparing
the ratio of PCR amplicon copy numbers to an added artificial standard. We found
that high ethanol concentrations indeed induce brittleness in insects. However, the
magnitude and nature of the effect varied strikingly among species. In general, ethanol
concentrations at or above 90% made the insects more brittle, but for species with
robust, thicker exoskeletons, this did not translate to an increased loss of appendages.
Neither freezing the samples nor drying the insects after immersion in ethanol had a
negative effect on the retention of appendages. However, the morphology of the insects
was severely damaged if they were allowed to dry. We also found thatDNApreserves less
well at lower ethanol concentrations when stored at room temperature for an extended
period. However, the magnitude of the effect varies among species; the concentrations
at which the number of COI amplicon copies relative to the standard was significantly
decreased compared to 95% ethanol ranged from 90% to as low as 50%. While
higher ethanol concentrations positively affect long-term DNA preservation, there is a
clear trade-off between preserving insects for morphological examination and genetic
analysis. The optimal ethanol concentration for the latter is detrimental for the former,
and vice versa. These trade-offs need to be considered in large insect biodiversity surveys
and other projects aiming to combine molecular work with traditional morphology-based
characterization of collected specimens.