Sunday, September 14, 2008

Killing Jars or Bottles


Killing Jars

Jars for use with liquid killing agents are prepared in one of two ways. One way (fig. A) is to pour about 2.5 cm of plaster of paris mixed with water into the bottom of the jar and allow the plaster to dry. Enough of the killing agent is then added to saturate the plaster; any excess should be poured off. This kind of jar can be recharged merely by adding more killing agent.

The second method is to place a wad of cotton or other absorbent material in the bottom of a jar, pour enough liquid killing agent into the jar to nearly saturate the absorbent material, and then press a piece of stiff paper on it or a cardboard cut to fit the inside of the jar tightly. The paper or cardboard acts as a barrier between the insect and the killing agent, keeping the latter from evaporating too rapidly and also preventing the specimen from becoming entangled in loose fibers.

Among the liquid killing agents are ethyl acetate (CH3CO2 • C2H5), ether (diethyl ether, C2H5 • O • C2H5), chloroform (CHCI3), and ammonia water (NH4OH solution). Ethyl acetate is most widely used. All of these chemicals are extremely volatile and flammable and should never be used near fire. Children should only use them under adult supervision. Ethyl acetate is regarded by many as the most satisfactory liquid killing agent. Its fumes are less toxic to humans than those of the other substances. Although it usually stuns insects quickly, it kills them slowly.

Specimens that appear dead may revive if removed from the killing jar too soon, but a compensating advantage is that most specimens may be left in an ethyl acetate killing jar for several days and still be limp. If the ethyl acetate is allowed to evaporate from the specimens, they will harden. Killing jars with ethyl acetate are preferred by many entomologists, especially for infrequent use.

Ether and chloroform are both extremely volatile and flammable and should not be used near an open flame or lighted cigarette. Their high volatility makes them serviceable in a killing jar for only a short time. Perhaps the greatest hazard with chloroform is that even when stored in a dark-colored jar, it eventually forms the extremely toxic gas phosgene (carbonyl chloride, COCI2). Chloroform, however, is useful when other substances cannot be obtained. It stuns and kills quickly but has the disadvantage of stiffening specimens.

Ethyl Alcohol (ethanol or ETOH) is widely used to kill small Coleoptera adults, small Hymenoptera, and many immature insects and soft-bodied insects. It is most commonly used at 70-80% concentration and many workers add 5% glacial acetic acid ("acetic alcohol") which helps penetration of the alcohol into the specimen and leaves specimens more relaxed. Isopropyl alcohol (rubbing alcohol) may also be used, and may be easier to find and purchase than Ethanol. However, Ethanol is preferred for most applications. Ethanol is used commonly in Berlese funnels and similar traps

Liquid ammonia is irritating to humans, and in general is not a particularly effective killing agent for most insects. However, it is highly recommended for use in small vials for dispatching microlepidoptera, and it has been used with variable success in blacklight traps, again for Lepidoptera. Specimens killed in ammonia tend to stay in a relaxed condition much longer than those killed by cyanide, allowing greater ease of spreading. Ammonia is readily available from many sources. Ammonium carbonate, a solid but volatile substance, also can be used.


References:

M. E. SCHAUFF. COLLECTING AND PRESERVING INSECTS AND MITES: TECHNIQUES AND TOOLS. Systematic Entomology Laboratory, USDA.

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