208 APPLIED ENTOMOLOGY 



Certain fungi live on the white flies, however, and are of assistance in their 

 control, but as they need certain weather conditions for their best growth during 

 about 3 months, they can rarely accomplish more than a third of the amount 

 of control necessary. 



Spraying with paraffin-oil emulsion prepared according to special directions 

 has proved to be a successful method of control for citrus white flies, and miscible 

 oil has also given good results. In either case the material as applied should 

 contain about 1 per cent of oil. 



Family Coccidae (Scale Insects). These are remarkable insects 

 having been much modified and changed in appearance from the more 

 ordinary forms. Without attempting an accurate classification, they 

 may be grouped under three heads: the armored scales, the soft scales, 

 and the mealy bugs. 



The mealy bugs are the least degenerate of the three groups. In 

 them the females preserve their body segments, eyes, antenna? and legs, 

 and can move about. They secrete a waxy material, usually as long 

 cottony threads or plates, more or less covering their bodies and some- 

 times forming a large egg sac at the hinder end. In the female soft 

 scales the antennaB and legs are not lost but they become reduced to 

 such an extent that though the adult can move about somewhat, it 

 seldom does so. Wax when secreted, is usually to form a sac at the hinder 

 end of the body enclosing the eggs, and the skeleton on the back of the 

 insect becomes very much thickened, forming a scale, often very convex, 

 strong and protective, though seemingly softer than in the armored 

 scales. In this last-named group the female loses antennae, eyes, and 

 legs, and secretes a waxy scale, with which the molted skins from the 

 body are felted together, forming generally a rather flat and very tough 

 scale. The metamorphosis in the females of all three groups is incom- 

 plete. In some cases the females are fertilized before they have attained 

 full size and grow considerably afterwards. 



The males develop much as do the females, at first, though not losing 

 any of their parts by degeneration. After reaching full size, however, 

 they pupate and emerge from the pupa as very tiny insects with only one 

 pair of wings and no mouth parts. Thus in the scale insects we have the 

 remarkable fact that while in the males there is a complete metamorpho- 

 sis, in the females it is incomplete. Whether the former was the original 

 condition in the group, and the females through the degeneration con- 

 nected with their mode of life have changed to an incomplete meta- 

 morphosis, or whether this was the primitive condition and complete 

 metamorphosis has been developed in the males, is unknown, though the 

 other Homoptera all have an incomplete metamorphosis. 



About 2,000 species of scale insects are known, attacking nearly all 

 kinds of trees and shrubs, and sometimes other plants as well. Many 

 have an almost incredible rapidity of increase, and when under favorable 



