Preserving specimens

Thrips can be preserved for 24-48 hours in alcohol. Place field collected specimens in a 70% solution of ethyl or isopropyl alcohol. For specimens intended for making permanent microscope slide mounts, the killing and preserving solution of choice is AGA. This is a mixture of 10 parts 60% ethyl alcohol, 1 part glycerin and 1 part acetic acid. Sources of these and other supplies are listed at the end of the section. This solution keeps the limbs and body supple and distended for mounting. Strong solutions of alcohol should be avoided, as they tend to harden the specimen.

Mounting thrips on microscope slides is tedious, and requires a bit of patience. One must balance the effort involved against the value of having a reference collection. However, such a collection is priceless when identifications need to be confirmed by a taxonomist, or if new personnel are to be trained in identifying thrips. By mounting a few specimens of each species encountered, a sizable collection can readily be produced. As species outside the scope of this article will surely be encountered, this will also provide an opportunity to expand one's horizons in entomology.

Slide mounts should fall into two categories:

Temporary mounts can be prepared with several commercially available mounting media. One that has produced good mounts, which when "ringed" will last for at least a few years, is CMC 10 (available from Masters Chemical Company, Inc., 520 Bonnie Lane, Elk Grove, Illinois 60007). Another popular temporary mounting medium, Hoyers's solution, produces good mounts, but they do not last as long as those made with CMC 10. Some batches of Hoyer's solution tend to dry out and crystallize even if the mount is ringed with a sealant, while others may last more than 20 years. CMC 10 has the added benefit of partially cleaning the mounted specimen after 24-48 hours.

Place a drop of mounting medium on a clean cover slip. Cleaning coverslips and slides with alcohol will remove grease, oil and dirt. Place the specimen onto the drop, and push it to the bottom of the drop with its ventral surface facing upward (the top of the body should be against the coverslip). Spread the wings and legs with a fine pin. If the surface of the mountant begins to dry, adding a small amount of alcohol or more mounting medium may soften it enough to avoid introducing bubbles. To avoid bodily distortion as the mounting medium dries, two or three shims, made of small pieces of crushed coverslip, may be placed around the specimen in the mounting medium at this time. Then lower a microscope slide slowly onto the drop of mountant. When the slide contacts the mounting medium, and the drop begins to spread, quickly invert the slide with the cover slip adhering to it. The specimen will now be in the proper orientation for examination. Final positioning and expulsion of bubbles can be done by gently pressing the coverslip with a needle. If the temporary mount is to be stored for any length of time, ringing the side with more CMC 10 or other sealant, such as clear fingernail polish, will keep the mountant from drying. For mounts intended for immediate use and disposal, this procedure may be greatly simplified. Slides prepared with Hoyer's solution should be heated gently at 110&deg for 7-14 days for complete cleaning and hardening.

Permanent mounts require using balsam as the mounting medium. The balsam should be of a medium consistency, neither too thin nor too thick. Balsam can be diluted with xylene.

Specimens for permanent mounts should be cleared by soaking in a solution of 10% potassium hydroxide. Before placing the specimen in the solution, a small hole is made in one of the intermediate abdominal segments with a very fine "minuten" pen. After the specimen has soaked for while, the macerated tissues can be expelled by pumping the body gently with a pin. After the specimen has cleared sufficiently, remove it from the solution and transfer for about 20 minutes to a solution of 45 parts distilled water, 20 parts glacial acetic acid and 50 parts 95% ethyl alcohol. This will neutralize the clearing agent and harden the specimen.

Specimens for balsam mounts must be dehydrated before mounting. This is done by transferring the specimens for several minutes into increasing concentrations of alcohol. The minimal series should include a bath in 95% ethanol, followed by a brief bath in 100% ethanol. This is followed by transferring the specimen to carbol-xylol for two to three minutes. (CAUTION: is Carbol-xylol is caustic and can burn the skin. If exposed, neutralize with alcohol and wash with water).

From this point, follow the procedure for temporary mounts substituting balsam for the temporary mounting medium. Balsam mounts should be dried for up to two weeks in a 100-120&deg F oven. A home oven with the incandescent light on works for this step. Observe the slides periodically, especially during the first 24 hours to make sure the specimens remain properly oriented, and to see if more balsam needs to be added.

Materials mentioned in this section can be purchase from the following suppliers. Other sources may also be available. Check local listings for alternative sources.

American Biological Supply Company
288 E. Green Street
Westminster, MD 21157
Telephone: 410 876-8599
Fax: 410 876-3438

BioQuip Products
17803 LaSalle Avenue
Gardena, CA 90248-3602 USA
Telephone: 310 324-0620
Fax: 310 324-7931

Carolina Biological Supply Company
2700 York Road
Burlington, NC 27215 USA
Telephone: 800 334-5551
Fax: 800 222-7112