244 XEW YORK STATE MLSEL'M 



abundance and almost universal presence of plant lice is strikint,dy illus- 

 trated by the fact thai an entire subfamily, the A])hidiinae, of these small, 

 parasitic flies are dependent, so far as known to scientific men. rntireh' on 

 these little insects for sustenance. There is another exceedini,dy interest- 

 ini^r enemy of certain jilanl lici- wjiich deserves notice because of the 

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

 a small butterfly. F e n e s e c a I a r (] u i n i u s I'abr., which may be found 

 feedint.,'' on masses of the collony jilanl lice, P (,- m p h i l;' u s tessellata 

 I'itch. sometimes so abundant on alders, and l)ctter known as tiie ahler 

 blight. 



Honeydew and its value to plant lice. I he above outlines brieth' some 

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

 life. The)' arc, as ])reviousl\' stalctl. comparali\el\- helpless and fall ready 

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

 wh\' the entire group had not l)ccn exterminated long ago. The fact is 

 that ajjhids, or ])lant lice, are al)le to exist on account of no defensive 

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

 brielly a few of the factors which enaljle this interesting and extensive 

 group to hold its place in the world of naturi-. .Most, it not all, species 

 of plant lice excrete a sidjstanci- known as hone)'dew which uiidoubtedh' 

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

 by various species of ants which are ever reatly to alTord more or less 

 protection to thi! producers. Some ants are very energetic in defending 

 these little ])lant lice and \\hene\-er a leaf bearing them is approached by 

 an enemy, they will c-ndt-avor to ])rotect tin; little honeydew proilucers .so 

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

 is picked and their ])rotectors at once turn and undertake to gi\'e battle to 

 the venturesome lingers. There are a sptcies of ants which carr\- this pro- 

 tection even further and tenderly care for the eggs or the ])lant lice them- 

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

 plants in the spring, in ortler that later tliey may reap the desired harvest of 

 honeydew. 'This excretion not only attracts certain species which render a 



