HEMIPTERA. 



155 



Owing to their small size and similarity in color, it is difficult to 

 distinguish the different species of Aleyrodes in the adult state. 

 But the immature scale-like forms present considerable differences. 

 The most common form that I have met is very flat, nearly 'circular 

 in outline, and furnished with a beautiful white fringe (Fig. 131); 

 this fringe is composed of parallel fibres, which radiate from the 

 margin of the body ; and its white color contrasts strongly with the 

 dark color of the insect. The segmentation of the body is often 

 represented by prominent wrinkles, which give the insect a minia- 

 ture resemblance to the fossils known to geologists as Trilobites. 

 Sometimes the fringe of excretion is 

 wanting; and in a common species on 

 maple, the excretion from the margin of 

 the body, instead of extending laterally 

 and forming a fringe, is directed towards 

 the leaf upon which the insect rests, 

 and thus the body is lifted away from FlG - *& Aleyrodes on maple, 

 the leaf, and perched upon an exquisite palisade of white wax 

 (Fig. 132). 



The American species of this family have not been studied. In 

 case any of them become destructive to vegetation, they can proba- 

 bly be destroyed by strong alkaline solutions, as are Coccids. 



Family IV. APHIDID.E.* 

 (Plant-lice^ 



The plant-lice are well-known insects ; they infest nearly all 

 kinds of vegetation in all parts of the country. Our most common 

 examples are minute, soft-bodied, green insects, with long legs and 

 antennae, which appear on various plants in the house and in the 

 field. Among our common species are both winged and wingless 

 forms. There are a great number of species, nearly all of which 

 are of small size. The bodies of our largest species measure only 6 

 or 7 mm. (0.24 or 0.25 inch) in length. 



The body is usually more or less pear shaped. The winged 

 forms have two pairs of delicate, transparent wings. These are fur- 

 nished with a few simple veins ; but the venation is more extended 



* Aphldidze, Aphis: perhaps from aphysso (dfivcro-w), to drink up liquids. 



