CHAPTER XIII. 
INSECT PESTS :—Their prevention and destruction. 
GREEN FLY OR ROSE APHIS.—(Sifhonophora rose). 
Most of the female aphis bring forth their young alive, 
two young having been produced in half-an-hour. Some 
broods of female aphis always produce their young alive, 
others always lay eggs. The young which are born alive 
begin to produce young in four to eight days. 
One female being once impregnated, her progeny bring 
forth young without further impregnation for many generations, 
and the progeny of one aphis after the end of one hundred 
days is said to possibly amount to 3,200,000 ! 
About the middle of September the last generation are 
produced, male and female; they pair and eggs are deposited 
in due course. These eggs hatch in spring, when all that are 
hatched are wingless females, which produce their young 
alive in a few days. After several changes of skin they 
become perfect insects either with or without wings; winged 
ones fly to fresh plants and found new colonies. Some 
females hybernate during the winter. 
The species of aphis just mentioned attacks many kinds 
of plants, but there are other species which seem to be confined 
to special kinds of trees; for example :—Aphis cerasi exists 
mainly upon the young shoots of the cherry ; aphis persicee, 
upon the peach and nectarine; aphis pruni, upon the plum 
and damson. 
Under glass all kinds of aphis may be kept in subjection 
by timely fumigation, but plants out of doors cannot 
conveniently be fumigated, and they must be kept clean by 
spraying and syringing. 
