188 INSECTS AFFECTING VEGETATION 



developing kernel. In about a week the eggs hatch, and the larvae 

 find their way at once to the kernel or germ. 



The life of the larva is about three weeks. The full-grown 

 larva is fairly robust, oval in shape, and has a length, when in a 

 quiescent state, of about eight-hundredths of an inch. When in mo- 

 tion, it extends somewhat and tapers markedly toward the anterior 

 extremity. It now abandons the wheat head and descends to the 

 ground. Many of the larvae are still in the wheat heads when it is 

 harvested and are carried away from the field when the wheat is 

 stacked. Their vitality under these circumstances is something ex- 

 traordinary, as they are able to survive for months without moisture 

 or food. Those that enter the ground in the fall form minute 

 cocoons not larger than a mustard seed, and when covered with dirt, 

 as they usually are, are almost impossible of discovery. It is be- 

 lieved that they remain unchanged in the ground until the following 

 spring, or probably until shortly before the appearance of the adult 

 insect again in the wheat fields in June. 



This insect is another one of the grain pests the ravages of 

 which are not subject to immediate remedy in the field. The only 

 steps of importance are in the line of prevention of future injury. 

 A practical preventive suggested by the hibernating habit of the in- 

 sect is in the deep plowing of the old wheat fields to bury the larvae 

 so deeply in the ground that they can not escape the following year. 

 As a further preventive, the chaff and screenings from the thrashings 

 of wheat from an infested field should be promptly burned. The 

 practice of rotation of crops is also applicable to this species and will 

 be of value in proportion to the isolation of the fields or to the gen- 

 erality of its adoption. 



The Wheat Plant-Louse. This plant-louse is not one of the 

 principal insect enemies of the wheat crop, but in some years, fortu- 

 nately widely separated, it multiplies in enormous numbers and over 

 wide regions, and becomes almost as destructive and occasions almost 

 as much loss as does the Hessian fly or the chinch bug. Local dam- 

 age is of more frequent occurrence, and the species, in fact, occurs 

 every year more or less, and often arouses fears which, for reasons 

 to be subsequently explained, are not realized. 



The wheat plant-louse appears on winter wheat in September in 

 the form of wingless females, which rapidly reproduce themselves, 

 going through several generations. It occurs about the base of the 

 wheat and on the roots, remaining in evidence as late as September 

 30. During the fall this louse does little damage to wheat growing 

 in good, fertile soil, and after the lice leave, the plants, as a rule, soon 

 recover. On poor soil, however, wheat may be seriously injured at 

 this season. The method of over-wintering has never been discov- 

 ered, but it seems probable that it hibernates on the wheat in the 

 egg stage. At any rate, the wingless female lice reappear on the 

 wheat early in April and remain in evidence, passing again through 

 many generations, until harvest. Throughout the spring and early 

 summer it works on the stems and leaves above ground. Later it 

 moves to the wheat heads, and very frequently these are simply filled 



