No. 115] 119 



noted for their injuries upon almost every known plant. There is 

 scarcely a vegetable growth that is free from their attack and many 

 of the long list of species known confine themselves to a single 

 species or genus of plant. They belong to the order of hemipterous 

 insects which take their food through a beak or proboscis which 

 they insert into the tissues and feed upon the sap. They are exceed- 

 ingly prolific, multiplying with marvelous rapidity, so that, as has 

 been computed, from a single egg, 729,000,000 may be produced in 

 seven generations, and some of the species have twenty generations 

 in a year. It is difficult to compute such multiplication — and 

 impossible to comprehend it. It will be readily seen that a multi- 

 plication even approaching the above would inevitably be fatal to 

 the vegetation upon which it depends for subsistence, entirely con- 

 suming all the sap of the young and first developing leaves. But 

 fortunately the young plant-lice are quite delicate and very suscept- 

 ible to certain meteorological conditions. Cold is destructive to 

 them, frost is fatal, as are also severe and continued rains. 



The myriads of the apple-tree aphis now upon the trees are from 

 the young which were hatched three or four weeks ago (the middle 

 of April) from small, shining black eggs which were deposited last 

 autumn in the crevices of the bark. When first hatched they resort 

 to the opening buds, which they frequently injure to an extent that 

 prevents their unfolding. Later they may be found distributed 

 over all the leaves, the under surface of which they puncture, causing 

 them to twist and curl and shrivel in the manner characteristic of 

 an aphis attack. At this season of the year all the aphides are 

 females and destitute of wings. They mature very rapidly and in 

 ten or twelve days are capable of producing young, which are 

 brought forth alive, about two daily, it is stated, for the period 

 of two or three weeks, when the female d?es. Her progeny con- 

 tinues to multiply with even greater prolificacy and rapidity as 

 with the advancing season the temperature increases. All this 

 occurs without the interposition of the male sex. It is not until 

 the approach of cold weather in the autumn that the males are pro- 

 duced, when, uniting with the females, the eggs above noticed are 

 deposited for the spring brood. 



During the month of July winged females will be found 

 associated with the wingless ones, both of which produce living 

 young. The winged females have the head, antennae (horns), 



