storing insects for morphology AND molecules

Doug Yanega dyanega at POP.UCR.EDU
Fri Apr 11 11:42:45 CDT 2003

>For morphology: what is the ideal concentration according to your experience,
>and how high can you go before material usually becomes too brittle,
>cecidomyiids are bad enough as it is in 70%? How long can you store
>really small
>Hymenoptera and Diptera before they degrade too much, and how much does
>temperature matter?
>For molecules: I have heard that 96% ethanol isn't necessarily the best. Yes,
>you get rid of the water, but the DNA might become fragile in the
>process so you
>might be better off even with 70%. Do you have any recommendations as to how
>long you can store material at different temperatures and ethanol
>Do you think that storing in 80% as cold as possible (maybe fridge temp) could
>be a possible compromise?
>If you have any recommendations it would also be valuable to know from which
>group(s), and when appropriate which gene(s), your experience applies to.

A published comparative study on recovery of DNA from samples
preserved in different concentrations of alcohol is very enlightening
(I can't recall the citation at the moment, sorry). The conclusions
were straightforward: the improvement in DNA preservation going from
70 to 95% was small but measurable (higher concentrations ARE better;
note that isopropyl alcohol was slightly worse than ethanol at equal
concentrations in this study, but still gave good results). This
means there *is* a trade-off - but it's not symmetrical; if you want
dry specimens for morphological study, that might easily tip the
scales in favor of using lower concentrations of ethanol. Is a 7%
improvement in DNA recovery worth a 70% increase in the rate of
abdomen collapsing, wing curling, or appendage breaking? I've never
worked with high concentrations of isopropyl, but if it doesn't have
the same effects on specimens, it might be better for general use.

Second, the temperature factor is EXTREMELY important. Even a single
day of heating (e.g., a malaise trap sample left in the sun, or on a
windowsill) can evidently ruin the DNA of a specimen permanently.
Aside from that, refrigeration of specimens is crucial if you need
*long-term* storage, both for preserving DNA and morphology (i.e., if
you process a sample within a week or two of collecting, and as long
as it isn't heated, the sample should be fine). Killing technique is
also crucial - DNA of specimens in pan traps (water or ethylene
glycol) deteriorates *very* rapidly, and can become worthless within
12 hours; ethyl acetate is also apparently extremely damaging to DNA,
in contrast to cyanide.

Hope this helps,

Doug Yanega        Dept. of Entomology         Entomology Research Museum
Univ. of California - Riverside, Riverside, CA 92521
phone: (909) 787-4315 (standard disclaimer: opinions are mine, not UCR's)
   "There are some enterprises in which a careful disorderliness
         is the true method" - Herman Melville, Moby Dick, Chap. 82

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