19 



corwergem Guer.,and Coccindla 9-notata Ilbst.. both of which, in the 

 adult as well as in the larval state, feed ravenously on the lice, though 

 the larvae are frequently suspected by grain growers of being the 

 parents of the liee, especially if found to be numerous in infested fields; 

 and larvae of various Syrphid flies and Chrysopids or lacewing flies, 

 which are even more voracious than those of the Coccinellids. 



Many of the lice are also killed by the larvae of a small and slender 

 black internal parasite, hysijphMms tritici Ashm., which preys upon 

 various species of plant-lice, frequently killing within a short time 

 huge colonies. The larva of this does not leave its host, but trans- 

 forms within the puffed up and empty shells of the aphides, many 

 of which may readily be observed adhering tightly to the stems or 

 blades of the grain. The little parasite, when ready to leave its host, 

 cuts out a neat circular piece, generally near the end of the body, and 

 through the opening it escapes. 



METHODS OF CONTROL. 



Owing to the practical impossibility of applying kerosene emulsion 

 or similar washes so as to destroy- insects which develop on standing 

 grain, particularly such as feed by suction, we must look to other 

 methods for the successful treatment of this plant-louse. Three or 

 four other forms of plant-lice usually occur in more abundance than 

 the species under discussion, and it has been found by experience that 

 these, as well as the present species, are very largely controlled by 

 natural conditions, sudden changes in the atmosphere, and such para- 

 sitic and other natural enemies as have just been considered. Lady- 

 birds and fungus diseases are the most important factors in reducing 

 the numbers of this pest. The year 1901 was particularly favorable 

 for the multiplication of this plant-louse in Texas, but. as usually 

 happens, the cool, moist weather of early spring, which favored the 

 increase of the pest, was followed later in the season by a sufficient 

 period of dry and sunny weather to enable the natural enemies, nearly 

 all of which are most active in such weather, to gain the ascendency, 

 and this they did, practically exterminating the lice in the region 

 affected. It should only be necessary to add that most other species 

 of plant-lice are controlled in precisely the same manner, and it is sel- 

 dom that they are destructive for more than one or two seasons in 

 succession. Examples are to be found in the cabbage louse, melon 

 louse, and the destructive green pea louse, which was such an enemy 

 to the pea industry throughout the more northern portion of our coun- 

 try during the years L899 and L900, from the Atlantic' coast to Wis- 

 consin. This last insect practically disappeared as a pest during L901, 

 and up to the date of writing has only appeared in numbers in a few 

 isolated localities, so far as we know, in the District of Columbia and 

 immediate vicinity. 



