ISO TRANSACTIONS OF THE ILLINOIS 



bands and spots of black ; the abdomen is flattened, and usually marked 

 with bands or partial bands of black. They are known in some sections 

 as "corn-flies," as they are often seen in great abundance, about the time 

 the corn is in bloom, hovering around the stalks, poised in the air appar- 

 ently almost motionless. Sometimes they are called "sweat-flies," from 

 the fact that on hot, sultry days they are must numerous. They drop 

 their eggs, one in a place, upon the leaves and twigs which are infested 

 with plant-lice, led by instinct to know that these will form appropriate 

 food for their young, although they, as perfect insects, feed on the sweets 

 of flowers and other similar food. The larvse which hatch from these are 

 maggots without any distinct head, not even possessed of eyes, but com- 

 pelled to seek their food by blindly exploring the surface of the leaf on 

 which they are placed. They are somewhat of an elongate wedge-shape, 

 blunt and broadest behind, and tapering forward to the front. When one 

 is feeding it elongates the front part of its body, and, feeling around until 

 it finds an Aphis, fastens upon it by its mouth, raises it in the air, and pro- 

 ceeds to suck the fluids from its body until nothing but the shell remains. 



These worms or maggots are usually of a transparent greenish or 

 whitish color, sometimes more or less clouded or spotted with other 

 colors. 



Quite a number of species belonging to the genus are found in 

 Illinois, but as these have not been identified, and I am not at present 

 su])plied with specimens, I am unable to give descriptions. 



Certain minute mites, belonging probably to the genus Trombidiutn, 

 have also been found preying upon plant-lice, and, as I suspect, also upon 

 their eggs. Some birds also assist in diminishing their numbers. 



This array of enemies, which might be greatly increased, will show 

 that nature has been careful to provide means for keeping in check these 

 prolific vegetable parasites, without whose aid plants would necessarily 

 soon be destroyed. 



ARTIFICIAL MEANS OF DESTRUCTION. 



The external envelope of the plant-lice is so delicate, and their hold 

 on life, so far as the individual is concerned, so easily broken, that they 

 are usually quite easily destroyed by the application of any acrid sub- 

 stance to their bodies. As they live out their entire lives on a very 

 limited portion of the plant they occupy, it follows that they must be 

 attacked directly, and while on the plants they infest. It is true that 

 there is usually one brood or generation that passes the winter in the tgg 

 state ; but so far the closest scrutiny has been enabled to follow but few 

 through tnis period, and the eggs are not only so minute as to render 

 their discovery difficult, but they are more tenacious of life than the adult 

 apterous individuals of the summer broods. It is apparent, therefore, 

 that the most accessible point and vulnerable period is during the sum- 

 mer, while they are at work upon the plants; and the remedy must be 

 one which will destroy the lice without injuring the life or value of the 

 plant. As they are too minute to be picked off by hand, even from the 

 most valuable plant, if at all numerous, and cling by their inserted beaks 



