1 68 AN INTRODUCTION TO ENTOMOLOGY. 



and devote the ground to some other use. Some other species of 

 tree can be safely planted in the same place, but not an apple. 

 Great care should be taken in putting out trees from a nursery to see 

 that they are free from this pest. If there is any doubt, the trees 

 should be washed, roots and all, in a strong solution of soap. It is 

 well also to put in the fork of the trees a piece of hard soap, which 

 will be dissolved and washed down by the rains. This will serve to 

 prevent certain other pests as well as the woolly aphis from getting 

 a foothold. In case it is desired to rid an infested tree of this pest, 

 the trunk form should be washed off with a strong solution of soap 

 applied with a sponge, taking care to destroy all eggs ; and the 

 ground should be treated with carbon bisulphide, as for the grape 

 Phylloxera. 



Sub-Family IV. 



The sub-family Aphidinae includes those genera in which the third 

 discoidal vein of the front wings is twice forked ; the hind wings have 

 two discoidal veins ; and the honey-tubes are usually well' developed, 

 sometimes tuberculiform or obsolete. The number of species belong- 

 ing to this group is very great ; it being the largest of the sub-families 

 of the Aphididae. Most of the species live above ground, on the 

 surface of leaves or twigs of woody plants or upon the leaves 

 and stems of the more succulent species. I do not know of any 

 species that produce galls. 



Ldchnus. The largest of our species of Aphididae belong to the 

 genus Lachnus. L. cdryce is found on the pig-nut 

 hickory, clustered on the under side of the limbs 

 in summer; it is interesting from being perhaps 

 our largest plant-louse, measuring to the tip of the 

 FIG. i 3 8. Lachnus. abdomen 6 mm. (0.24 inch), and more than 10 mm. 



(0.4 inch) to the tip of the wings. 



Aphis. To the genus Aphis, in its restricted sense, belong a con- 

 siderable number of the important species of this sub-family. The 

 species that occurs in such immense numbers on cabbage is Aphis 

 brassicce. It is the mpst common, and, perhaps, the most injurious 

 species that occurs in the vegetable gardens of this country. The 

 Corn Plant-louse is Aphis maidis. This species, according to the 

 observations of Forbes, winters in the wingless, agamic form in the 

 earth of fields previously infested. In the spring it appears to be 

 strictly dependent upon a species of ant, Lasius alienus, which mines 

 along the principal roots of the corn, collects the plant-lice, and 



