THE EUROPEAN CORN BORER AND ITS CONTROL. 21 



soon fall to the ground. This forms a mass of intertwined plants very 

 difficult to remove or destroy during ciean-up operations. 



The chief economic signihcance of barnyard grass as a food plant of 

 the European corn borer lies in the fact that it serves as a common host 

 of the insect, and aids in its multiplication and distribution in areas where 

 corn is absent. 



Pigweed, or redroot, is commonly found growing among cultivated 

 crops, or closely adjacent thereto. It generally serves as a sort of over- 

 flow host plant to accommodate the larger larvae of the corn borer which 

 have left their original host plant and are seeking other food. 



In rare instances newly hatched larvae are found feeding upon the 

 green seed heads of this plant. This is generally caused by the dislodg- 

 roent of these larvae from their original host. 



More commonly the plant is attacked by good-sized larvae which have 

 partly completed their development in other food plants. The stalk is 

 entered at any point along its surface, and the larva tunnels upward or 

 downward in the same manner and with the same results as have been 

 mentioned for other food plants. 



Pigweed is not generally infested by the European corn borer with the 

 same degree of severity as are dock and barnyard grass, although it is 

 important economically as an intermediate host of the insect, and may 

 act as a host in the absence of more favored food plants. 



Ragweed and Lamb's-quarters. 

 Ragweed, or hogweed, and lamb's-quarters serve as food plants for the 

 European corn borer in the same manner and extent as has been described 

 for pigweed. The larvae attack the green seed head and stalk of each 

 of these plants. Lamb's-quarters sometimes grows to a height of 4 or 

 5 feet, and develops a tough, woodj- stalk an inch or more in diameter. 

 It is perhaps the hardest and toughest stalk in which the larvae of the 

 European corn borer have been found. 



. Both ragweed and lamb's-quarters are found widely distributed through- 

 out the infested area, although the number of plants found in a given 

 space is generally small. 



Dahlias. 

 Larvae of the European corn borer tunnel through the main stalk and 

 flower stems of dahlias during the late summer and fall. The percentage 

 of dahlias in a given area, infested by the larvae, is generally very high. 

 In Arlington, and other towns adjacent to Boston, almost every group of 

 dahlia plants was found to be infested by P. nubilalis during the past 

 summer. Small larvae are rarely found in dahlias, most of the damage 

 being done by those which have hatched and fed for a time on other 

 plants in the vicinity, and are about half grown when they enter the 

 dahlia plants. Entrance may be effected at almost any place along the 



