There are different ways of killing insects. Each one has its advantages and disadvantages, but the following are the best options available.
This is a simple and efficient method that does not require any chemicals. In fact it is the best one to use whenever possible. Just put the specimen in the freezer for at least three days. Ideally, you should use one container for each insect. Include your collection notes, and place a piece of paper towel in the container to prevent condensation.
It is better to keep insects in the freezer longer than to get an unpleasant surprise if the insect you are pinning starts moving. This is especially important for bumble bees and wasps caught in the spring; they have spent the winter as adults and can better tolerate the cold.
Of all the products available, ethyl acetate is the best. It is a colourless liquid poison that is considered quite safe for humans, provided it is used properly.
It takes about 30 minutes to asphyxiate most small arthropods, and about an hour for larger ones. To use ethyl acetate, prepare a killing jar: a tightly sealed container (a jar or tube) containing material to absorb the poison, of the proper size for the insect to be killed.
If you opt for a tube instead, fill it halfway with hardwood sawdust. It will absorb the poison, while protecting the insect from damage. Before you go out insect hunting, place a few droplets of ethyl acetate on the sawdust. The insect will sink into the sawdust and die. You can place more than one insect in a tube, especially if they are small.
If you are using a glass or sturdy plastic jar, place some absorbent material in the bottom of the container (cotton batting, sawdust or felt). Prepare the jar before you go out collecting, by adding a few drops of poison.
Make sure you label the bottle of ethyl acetate and all your killing jars with “POISON: ETHYL ACETATE.” Store them in a safe place.
Insects that will be displayed in alcohol may also be killed with alcohol. Larvae, soft-bodied adults and tiny beetles should be placed directly in 70% or 75% isopropyl alcohol (rubbing alcohol), available from drug stores.