CHAPTER VI 
GALLS INDUCED BY PLANT-LICE (HOMOPTERA) 
HE order Hemiptera comprises insects provided with 
X a mouth specially adapted for piercing the tissues and 
sucking the sap from the plants on which they feed. It 
contains two suborders, Heteroptera and Homoptera. In 
the insects classed under the former the anterior wings are 
of unequal consistency, and the front of the head does not 
touch the coxae ; in those of the latter the anterior wings 
are homogeneous, and the front of the head and the coxae 
are in contact. With the Heteroptera we are not concerned; 
two representatives of the family Tingidae —viz., Copium 
clavicorne Linn, and C. tcucrii Host.—deform the flowers of 
Teucrium chamaedrys and T. montanum on the Continent, but 
I am not aware of their occurrence in Britain. Three 
families of the Homoptera contain gall-causing insects—the 
Aphid ae , or “ green-fly” ; the Psyllidae (springing plant-lice 
or leaf-fleas); and the Coccidac (scale insects and mealy¬ 
bugs). 
The majority of homopterous gall-causers are Aphidae. 
Most people are acquainted with them under the names of 
“blight” and “green-fly.” These insects are remarkable 
for the enormous production of young by parthenogenetic 
females, and the rapidity with which the young themselves 
attain the same function ; within a summer the progeny of 
a single individual is almost innumerable. Huxley calcu¬ 
lated that the produce of a single Aphis would, if all the 
individuals survived, in the course of only ten generations 
“contain more ponderable substance than five hundred 
77 
