Naphthalene is chiefly repellent in action; its odor keeps out pests, but, if they are already in the specimen boxes, naphthalene will usually not kill these pests, and some other substance must be used.
Paradichlorobenzene, called PDB, is a good fumigant to use on pests in the collection. It should be used in a nearly airtight container, such as a tight trunk, bin, or case, at the rate of 1 pound of PDB to 25 cubic feet of space. The boxes of specimens, with lids open or removed, should be placed in the container, the fumigant scattered or spread on a piece of cloth or paper above them, and the container sealed for about a week.
Fig. 17.—A naphthalene mothball mounted on a common pin. It serves as a repellent to keep away from the collection live insects that might cause damage. To insert the pin, stick the point in a cork, heat the head in a flame, and then push the head into a mothball. The pin will melt its way into the naphthalene, which will cool and harden again almost immediately.
THE INSECT WORLD
When the insects have been collected, mounted or preserved, and labeled, the next step is to identify or name them. This is no easy task, because there are so many different kinds of insects. In the whole world there are well over 1 million different kinds and in Illinois alone probably 20,000 different kinds.
The identification of insects is simplified somewhat by the fact that many species are closely related and can be classified into a number of major groups. Insects as a whole constitute what is called a class of animals, the Insecta. The crabs, shrimps, and their allies constitute a class called the Crustacea; the snakes, turtles, lizards, and their allies constitute another class called the Reptilia; and so on. The entire insect class is divided into orders, such as the Coleoptera, or beetles, the Diptera, or flies, and the Siphonaptera, or fleas. Each of these orders may contain several dozen to 25,000 different kinds of insects in North America alone. These orders are divided into families, each of which may contain one species to many thousands of species. The family names always end in -idae, as in Pentatomidae, the name for the stink bugs. The families are divided into genera (the plural for genus), and the various species (the word is the same for both singular and plural) or kinds are placed in the genera.
The house fly bears the name Musca domestica Linnaeus; this means that the species name is domestica, that the name was first applied to the species by Carolus Linnaeus (known as the describer of the insect or the author of the name), and that the species domestica is in the genus Musca. The genus Musca belongs to the family Muscidae, which, in turn, belongs to the order Diptera of the class Insecta.
Scientists may decide that a certain species belongs in another genus. When the species is transferred from the genus in which it was originally described to another genus, the name of the author is placed in parentheses. For example, the chinch bug was originally described by Thomas Say in the genus Lygaeus and had the name Lygaeus leucopterus Say. Later the species leucopterus was transferred to the genus Blissus, and Say’s name was placed in parentheses, thus: Blissus leucopterus (Say).
In the process of growth, insects go through a series of interesting stages. When the immature insect reaches a certain size, its outside skin covering or cuticle will not stretch further and the insect then acquires a larger cuticle by a process called molting.