6 THE COCCIDAE 



appearance of different individuals of the same species due to 

 their being crowded into crevices and depressions upon the host- 

 plant and also to the close crowding together of the different 

 individuals. While there is considerable variation in the form and 

 structure of the body, these differences are always so minute that 

 they can not be seen without the aid of a miscroscope and many 

 of them are difficult to interpret even by the use of a microscope 

 of considerable magnification. In the classification of coccids the 

 early systematists used the superficial characters, those based on 

 the shape and consistency of the wax. Comstock demonstrated 

 not only the validity of the structural characters of the pygidium, 

 but used them in differentiating species of Diaspidinae so that it 

 is now possible with a considerable degree of accuracy to identify 

 species of this subfamily. The genera and species of the other 

 subfamilies are still based to a large extent upon superficial 

 characters. 



The greatest development in number of genera and species is 

 found in tropical and subtropical regions, but many genera and 

 species extend into and are peculiar to temperate regions. The 

 number of peculiar or ' bizarre species that have been described 

 from Australia and the islands connecting this continent with the 

 Asiatic mainland is large. While certain species of coccids are 

 found only upon certain plants and frequently only upon certain 

 parts of the plant, other species whether limited to a particular 

 part of the plant or not may occur on all the species of plants of 

 a genus, of a family, or all the families of an order. Some species 

 are found apparently indiscriminately upon almost any plant, 

 regardless of its taxanomic association and upon any part of the 

 plant but the roots. Only a few coccids feed upon the roots of 

 plants. They are peculiar to this situation and belong as a rule 

 to particular coccid genera. 



The individual insects are usually small and inconspicuous 

 and easily overlooked. While this is true of most coccids, some 

 of the species of the generalized subfamilies attain a size of one 

 inch or more. Many of the large or medium sized species are 

 conspicuous in the adult stage because of the mass of white wax 

 which surrounds their body or its attachment to it. This is partic- 

 ularly true of colonies of Pulvinaria which are usually overlooked 

 until they begin to form their ovisacs. The amount of wax 

 excreted by the female before and during the deposition of her 

 eggs varies with the subfamily and to a certain extent with the 

 species. Some females excrete a long ribbon of doughy wax five 



