SUMMER MEETING. 137 



by the slower method of the lajiog and hatching of eggs, as is the 

 rale iu the developmeut of insects, accounts for their appearance in 

 such vast numbers, and, insignificant as they are individually, places 

 them in the rank of the most formidable enemies of vegetation. 



The life history of the various species, though subject to much 

 variation, may be summarized as follows: 



Very early iu the spring single aphids hatch here and there on the 

 swelling buds of the plants subject to them. Bach of these becomes 

 what is called a "stem mother," and is capable of a certain kind of repro- 

 duction without mating. In about a week, if the season is favorable, 

 this insect, of which the average size is about that of a mustard seed, 

 begins to produce living and fully formed young by a process similar 

 to budding in plants. From six to ten are often brought forth in 

 twenty-four hours. The first act of each of the young is to plunge its 

 invisibly fine beak into the tissues of the leaf on which it finds itself 

 and begin extracting the sap. In from four to six days it also begins 

 to reproduce in the same manner and quite as rapidly as the stem 

 mother, which, in the meantime, has gone at the same rate, adding to 

 her colony. In this way the crowded groups, so often noticed, are 

 easily accounted for. 



Later in the season when the leaves and young shoots are not so 

 full of sap the individuals scatter more, and on the worst infested 

 plants where the foliage has begun to dry, a large proportion suddenly 

 acquire wings and are thus enabled to migrate to new food plants. 

 Indeed, this migrant form develops, after a time, in every colony, even 

 when tht^re is no lack of nourishment. In the autumn, in most species, 

 winged males and true wingless females appear and, after pairing, the 

 latter seek the tips of the new shoots or scatter over the bark of trees 

 and lay the eggs from which the stem mothers are produced the fol- 

 lowing spring. These winter eggs, usually black, shining atoms with 

 very hard shells, are difficult to destroy, but a thorough drenching 

 with rather strong kerosene emulsion, or whale oil soap suds, which 

 may be used with safety on a tree or shrub in its leafless state, will 

 prevent hatching and thus nip the whole plant-louse plague in the bud. 



Those who suffered so severely from these pests this spring should 

 bear this fact in mind and treat their trees according to directions dur- 

 ing mild spells in winter or very early in the spring. 



It is almost exasperating to see what provision nature has made 

 against the extinction of these, to us, so objectionable forms of life. 

 The species that are destructive to annual or herbaceous vegetation, 

 in the autumn instinctively migrate to shrubs and trees or to the roots 

 of grasses or other perennials on which, in the spring, the stetn moth- 



