Systematic Position of Aleyrodes. 



The two genera, Aleyrodes Latreille and Alenrodicus Douglas, 

 constitute the family of Homoptera* called Aleyrodidae. The latter 

 genus is distinguished from the former by the presence of a distal 

 and a basal branch to the median vein in both pairs of wings. The 

 insects of this family were for a long time classed with the Coccidae, 

 or scale insects, on account of the resemblances between the imma- 

 ture stages. The differences between the two groups of insects in 

 their metamorphosis and the form of the adults have been used as 

 the chief characters to distinguish the family Aleyrodidae from the 

 Coccidae, and the former is now given a systematic position between 

 the latter family and the Aphidae, or plant lice. The larval and 

 pupal stages of the Aleyrodidae are distinguished from those of the 

 Coccidae by an opening on the dorsum of the last abdominal seg- 

 ment known as the " vasiform orifice." The insects undergo a com- 

 plete metamorphosis, thus differing in a marked degree from all other 

 Homopterous insects, except the Coccidae, where the male alone un- 

 dergoes a complete metamorphosis. In both these families the 

 metamorphosis, though complete, is of a peculiar nature, and differs 

 in some respects from that of the true Metabola, or such insects with 

 complete metamorphosis as Lepidoptera (butterflies and moths), 

 Diptera (flies), and Coleoptera (beetles). Both males and females 

 of the Aleyrodidae have in the adult condition two pairs of well- 

 developed wings, while in the adult male Coccidae the hinder pair of 

 wings is represented by minute appendages called halteres. There 

 is much evidence to show that incomplete metamorphosis is the an- 

 cestral condition of insects, and therefore in general, insects with 

 complete metamorphosis represent a higher degree of specialization 

 and are younger than those which have retained the former condi- 



* For the benefit of those who are not familiar with the classification of insects, it is 

 here explained that the Homoptera and Heteroptera are two sub-orders of the Hemiptera. 

 The former is distinguished from the latter by the form of the wings, which are of the same 

 thickness throughout and usually sloping at the sides of the body, and by the position of 

 the origin of the beak, which is at the hinder part of the lower side of the head. The Hom- 

 optera include such insects as plant lice, scale insects, cicadas and leaf hoppers. To the 

 Heteroptera belong the true bugs, such as the squash bug and chinch bug. 



