80 ENTOMOLOGY. 



Family Aleyrodidae. — Wings rounded, rather broad and white; larvae 

 scale-like and fixed to leaves; beak 2-jointed. Aleyrodes eorni Hald. 



Family Aphidse. — The Aphides or plant-lice abound to an enormous 

 extent; nearly every plant has one or more species peculiar to it, and 

 the individuals are often to be numbered bj T millions; while a thousand 

 species are already known. The males and females are usually 

 winged; in rare cases are the males wingless, but the females are not 

 seldom without wings, while the asexual individuals are wingless. 

 They are all small insects, both sexes with a 3- jointed beak; the wings 

 have few veins; the body is flask-shaped, and in the species of Aphis 

 and Lachnus near the end of the abdomen are two tubes for the exit 

 of a sweet fluid called " honey dew," which is lapped up by the ants 

 seen frequenting a colony of these insects. Aphides are usually 

 green, with a soft powdery bloom on the skin. 



The Aphides or plant-lice abound by reason of their wonderful 

 fertility, the young being brought forth alive. There are as many as 



Fig. 66.— Apple Aphis. Natural size and enlarged. 



nine or ten generations; a single Aphis becoming the parent in one 

 summer of millions of children and grandchildren. Though they are 

 devoured in enormous numbers by other insects and by birds, still 

 hosts are left to prey on our fruit-trees, succulent vegetables, and 

 household plants. Thus, these weak, defenceless creatures owe their 

 success in life to their unusual powers of reproduction, the young 

 budding forth within the parent, as the polyp sends forth bud after 

 bud which eventually become jelly-fish. The last brood of Aphides 

 lay eggs in the autumn and then die. 



Sexual forms (at time of birth already mature, wingless, and with- 

 out a proboscis) sometimes occur in the spring, as in the European 

 Pemphigus terebintM (Peilus). Chermes and Phylloxera eive birth 

 in place of viviparous generations to a special egg-laying female, 

 which also produces eggs, from which arise individuals which repro- 

 duce parthenogeiietically. In Phylloxera guercus, besides the two 

 generations, there is another general ion which appears in autumn, and 

 consists of very small males and females i without a suctorial proboscis 

 or alimentary canal). These animals arise from two kinds of eggs 

 which are laid in the roots. The female after pairing lays only a 

 single egg. It is the same with the Phylloxera of the vine (Claus). 

 Of the latter there are two forms, one living in galls on the leaves, and 

 the other forming small swellings on the roots. The root-form is 

 either wingless or winged, the latter very rare. The leaf-form is said 

 to be always wingless. 



