SUSTAINING THE WORLD THROUGH SCIENCE AND TECHNOLOGY

Specimen Preparation


Professional techniques for specimen identification or vouchering
Preparation of specimens for collection

For traditional taxonomic purposes, delphacids are mounted on insect pins.  Generally, stainless steel pins are preferable to black enamel, but are more expensive.  Because delphacids are small, they should be pointed (rather than pinned, double mounted, or glued on cards).  This procedure is described in most general entomology texts, but will be briefly described here.  The ‘points’ are small, roughly triangular bits of acid-free, high quality, heavy gauge paper, usually punched using a specialized insect point-punch (which are surprisingly expensive).  Aid-free paper should be used (such as insect label paper or botanical specimen mounting paper) because acid paper (such as index cards) turns yellow and becomes brittle over time.  Using the best materials insures that the specimens will be scientifically useful for a very long time.  The point glue should be a material that does not degrade over time, is soluble (in alcohol or water) so that the specimen can be removed from the point if required, and does not in any way compromise the specimen.   Many workers use white glue, but the Association of Systematic Collections some years back (before they became part of the Society for the Preservation of Natural History Collections) recommended a polyvinyl acetate resin (AYAF grade), such as Gelva, which is alcohol soluble (the reasons for this recommendation were not entirely clear).  Delphacids are prepared by pinning the point (the point should be 1 centimeter from the head of the pin to give a handle to grasp the pointed specimen), bending the tip of the point over slightly, applying the glue to the tip of the point, and then the point to the side of the insect. Usually, the point is applied to the right side of the insect (because scientific illustrations are most often made with the insect head to the left, and this leaves the same side of the insect available for viewing) on the thorax (not the legs or wings, because these will break off eventually and the specimen may be lost, and not on the abdomen because the abdomen may need to be removed for dissection).  The finished specimen should ideally be straight both in the horizontal and vertical axes. 

Labels for insect specimens

In addition to mounting the specimen properly, there is the matter of the information that goes with the specimen.  Having accurate and complete information makes specimens very valuable from the scientific standpoint.  While the insect specimen itself may provide information regarding color or morphological variation of the species, it is the insect label that provides most of the information about the temporal and special distribution of a species, habitat and host records.  The label information should also be precise, unequivocal, and self-explanatory so that users of the specimens will be able to properly interpret the label data, and abbreviations should be used with care so that they are understandable in the context of the label information.  The details of how the information is organized on the labels are less important than having the label information clear and complete.  Some entomologists prefer a two label system (with locality on the top label, and date-collector-habitat/host on the second), but entomologists that prepare large numbers of specimens usually prefer a single label system.  In either case, the label font side should probably be no less than 4.0, and the maximum label size approximately 8x12mm.  Suggested information and format for the label information is organized from general to specific (often with the country in all caps), the date collected (day, month, year, with month in roman numerals),  collector, collecting method, habitat or host (when known).

For example:

COUNTRY, state
County, town
Specific location
G.P.S.
Date
Collector
Method/habitat/
Host
USA, Virginia
Northamton Co.,
Cape Charles, nr. Bay Ave
371610N, 760121W

21.ix.2009,
C. Bartlett
Sweeping
Ex: Spartina patens
or

USA: Virginia, Northampton
Co., Cape Charles nr. Bay
Ave., 21.ix.2009, C. Bartlett
371610N, 760121W
Sweeping Spartina patens


Specimen preparation for identification

The identification of specimens usually requires males, and often the male genitalia need to be 'cleared' for examination.  Clearing the male genitalia involves breaking off the abdomen and placing it in 10% potassium hydroxide (KOH; or sodium hydroxide, NaOH) solution.  Most often, a cold KOH solution is used, with the specimens left overnight for clearing.  Hot KOH can be used to clear specimens within a half hour, but KOH (particularly hot KOH) is caustic, and specimens are easily over-cleared if not carefully attended (not to mention that hot KOH may be dangerous).  To break off the abdomen of a pointed specimen, turn the specimen upside down and push on the abdomen (to avoid damaging the genitalia, do not press on the pygofer); usually the abdomen will snap off at the base (at the tymbal mechanism), as long as the base of the abdomen is not covered with point glue.  Sometimes the abdomen may suddenly snap off – it is a good idea to clean you workspace and perform this task within some type of container so that the abdomen can be easily found if abruptly dislodged.  The abdomen can then be placed in KOH for clearing.  When performing multiple dissections, be sure that the specimens and their abdomens can easily be associated without confusion later (usually by numbering the specimens and the clearing wells).

A cleared abdomen will still have color, but will be flexible without being brittle.  The soft parts of the anatomy will be easily dislodged and removed by gently tamping the abdomen.  When the abdomen is ready to be removed from the KOH, place the abdomen in a water rinse and tamp out the abdomen contents to remove any remaining KOH (multiple rinses may be desired, or carefully neutralizing the KOH with a mild acid), then move the abdomen into glycerin.  Sometimes the cleared abdomen will be sufficient to view the needed features, but often the aedeagus will need to be everted.  This can be done by gently removing the pre-genital segments of the abdomen from the pygofer, then gently pushing the aedeagus with insect pins or a fine pointer from behind to evert it.  Often the pygofer must be held in place while pushing on the base of the aedeagus.  Considerable care should be taken to not tear the pygofer while pushing on the aedeagal base.   When the aedeagus is everted, segment 10 (the "anal tube") will rotate anteriorly; sometimes rotating segment 10 will evert the aedeagus instead of pushing at the aedeagal base.  When this process has been successfully completed, the aedeagus should be visible in  lateral view, unobstructed by the pygofer (except possibly at the very base).