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NEW YORK STATE MUSEUM 



abundance and almost universal presence of plant lice is strikingly illus- 

 trated by the fact that an entire subfamily, the Aphidiinae, of these small, 

 parasitic flies are dependent, so far as known to scientific men, entirely on 

 these little insects for sustenance. There is another exceedingly interest- 

 ing enemy of certain plant lice which deserves notice because of the 

 remarkable divergence in food habits from its allies. It is the caterpillar of 

 a small butterfly, Feneseca tarquinius Fabr., which maybe found 

 feeding on masses of the cottony plant lice, Pemphigus t e s s e 1 1 a t a 

 Fitch, sometimes so abundant on alders, and better known as the alder 

 blight. 



Honeydew and its value to plant lice. The aliove outlines briefly some 

 of the factors with which aphids or plant lice must contend in the battle for 

 life. They are, as previously stated, comparativeh' helpless and fall ready 

 victims to all of these agents, and one unfamiliar with nature might wonder 

 why the entire group had not been e.xterminated long ago. The fact is 

 that aphids, or plant lice, are able to e.xist on account of no defensive 

 powers of their own, but must rely on other means. We will discuss 

 briefly a few of the factors which enable this interesting and extensive 

 group to hold its place in the world of nature. Most, if not all,, species 

 of plant lice excrete a substance known as honeydew which undoubtedl)' 

 serves indirectly as a method of protection, since it is eagerly sought after 

 by various species of ants which are ever ready to afford more or less 

 protection to the producers. Some ants are very energetic in defending 

 these little plant lice and whenever a leaf bearing them is approached by 

 an enemy, they will endeavor to protect the little honeydew producers so 

 far as possible. This is apparent when a leaf bearing a few of the aphids 

 is picked and their protectors at once turn and undertake to give battle to 

 the venturesome fingers. There are a species of ants which carry this pro- 

 tection even further and tenderly care for the eggs or the plant lice them- 

 selves during the long winter and establish them on the roots of proper food 

 plants in the spring, in order that later they may reap the. desired harvest of 

 honeydew. This excretion hot only attracts certain species which render a 



