THE MONTHLY BULLETIN. 59 



HABITS OF SOME COMMON PLANT LICK. 

 By C. P. Gillette, State Entomologist, Colorado. 



The Aphids, commonly spoken of as "plant lice," are among the 

 smallest, weakest and apparently the most .stupid of insects, with meager 

 powers of defense, or means of escape from their enemies. Yet, these 

 seemingly most unfit creatures of the insect kingdom are, for some 

 cause, remarkably "fit" from the standpoint of the evolutionist, for 

 they have been able to live and propagate their kind and become 

 extremely abundant, in spite of the many natural enemies that con- 

 tinually prey upon them. 



The lady-beetles, in both their larval and adult stages, feed vora- 

 ciously upon the plant lice, which they devour bodily much as a cat 

 eats a* mouse. They are one of the most efficient natural agencies for 

 the control of plant' lice. .Miss M. A. Palmer, who made a study of the 

 life histories and food habits of several of our most common species 

 of lady-beetles, took the pains to count the aphids she fed to them and 

 announced the approximate number required as a life ration for a 

 ile during the larval stage as varying from 264 to 621, depending 

 on the species. Adult beetles ate, or partially devoured, as many as 

 200 in one day. 



The Syrphus Hies, which, in Colorado at least, are the most efficient 

 natural enemies in the control of plant lice, and the aphis lions, which 

 are very destructive to some species, destroy their victims by merely 

 sucking their blood. Because of this habit of feeding upon the body 

 fluids only, these aphis destroyers require a much larger number of 

 insects for food than would be needed if they devoured their victims 

 bodily. 



Many species of aphis are destroyed in countless numbers by minute 

 Hymenopterous parasites that feed within the bodies of their hosts. 

 The Braconida .are especially destructive in this manner. Certain 

 call-forming species, such as Eriosoma americana of the elm and 

 E. lanigera of the apple, tire destroyed by Capsid marauders, which 

 should, according to our ideas of propriety, feed only upon the leaves 

 of plants. 



Many other enemies of lesser importance might be mentioned, but 

 those already given are sufficient to call attention to the severe struggle 

 for existence that the aphids have to carry on continually. In spite of 

 it all. nature has provided abundant ways by which these apparently 

 helpless creatures may live on from year to year and from generation to 

 generation. They positively thrive amidst the terrible carnage that 

 goes on continually wherever they establish their colonies. 



What are some of the reasons that these minute insects are able to 

 maintain their existence against what seem to be tremendous difficulties .' 

 First, and most important, is their wonderful power of reproduction. 

 .Many of the species exist as viviparous females, no males being known 

 at any stage of their development. Most of the species with which 

 fruit grower is familiar spend the winter in the egg stage, all the 

 individuals of the year dying off when cold weather comes. These eggs 

 are nearly always deposited about the buds of trees or shrubs, and 

 batch early in the spring. Hatching usually takes place a little before 



