17.2.2. Fixing and wet preservation
Most eggs, nymphs, larvae, pupae, puparia, and soft- bodied adults are preserved in liquid because drying usually causes them to shrivel and rot. The most commonly used preservative for the long-term storage of insects is ethanol (ethyl alcohol) mixed in various concentrations (but usually 75–80%) with water. How- ever, aphids and scale insects are often preserved in lactic-alcohol, which is a mixture of 2 parts 95% ethanol and 1 part 75% lactic acid, because this liquid prevents them from becoming brittle and facilitates subsequent maceration of body tissue prior to slide mounting. Most immature insects will shrink, and pigmented ones will discolor if placed directly into ethanol. Immature and soft-bodied insects, as well as specimens intended for study of internal structures, must first be dropped alive into a fixative solution prior to liquid preservation. All fixatives contain ethanol and glacial acetic acid, in various concentrations, combined with other liquids. Fixatives containing formalin (40% formaldehyde in water) should never be used for specimens intended for slide mounting (as internal tissues harden and will not macerate), but are ideal for specimens intended for histological study. Recipes for some commonly employed fixatives are:
- KAA — 2 parts glacial acetic acid, 10 parts 95% ethanol, and 1 part kerosene (dye free).
- Carnoy’s fluid — 1 part glacial acetic acid, 6 parts 95% ethanol, and 3 parts chloroform.
- FAA — 1 part glacial acetic acid, 25 parts 95% ethanol, 20 parts water, and 5 parts formalin.
- Pampel’s fluid — 2–4 parts glacial acetic acid, 15 parts 95% ethanol, 30 parts water, and 6 parts formalin.
- AGA — 1 part glacial acetic acid, 6 parts 95% ethanol, 4 parts water, and 1 part glycerol.
Each specimen or collection should be stored in a separate glass vial or bottle that is sealed to prevent evaporation. The data label (section 17.2.5) should be inside the vial to prevent its separation from the specimen. Vials can be stored in racks or, to provide greater protection against evaporation, they can be placed inside a larger jar containing ethanol.