26 THE SUGAR-BEET WIREWORM. 



ACTIVITY OF THE WIREWORMS. 



During the spring, when the soil is kept wet by the rains and loose 

 by cultivation., it is probable that tlie wire worms are able to travel 

 from one beet plant to another. Under laboratoiy conditions they 

 have been noted to travel several inches daily, in the root cages, and 

 the soil then is very apt to be compacted by wetting. This point 

 was tested by placing several wire worms in a root cage without food 

 in order to compel them to move. The soil, which was quite damp 

 at first, was allowed to become pretty thoroughly dry, and then the 

 cage was watered. The water followed the channels of the wire- 

 worms, and in this way the wireworms could be easily traced by the 

 wet streaks through the soil. These cages were 18 by 24 inches, yet 

 m the week or 10 days the soil was drying out the wu-eworms had 

 been able to channel all through the soil. Late in the summer, when 

 the soil is more dry and compact, they move about much more 

 slowly and are less anxious to feed, but as they do all their damage 

 in the spring their actions at the latter time are of the utmost impor- 

 tance. From all the observations on their activity it seems not only 

 possible but even probable that one wireworm can destroy several 

 young beet plants in a season. The sugar-beet plants are from 6 to 

 8 inches apart in the rows. 



WIREWORM INJURY TO BEETS. 



During the latter part of February and in March and April the 

 ravages of the wdreworms in the beet fields are very noticeable, 

 especially so when the insects are present in numbers. In a year 

 such as 1912, when their work was well scattered, injury can be 

 noted, but it is possible to overlook it. 



When the young beet plants are attacked they wilt, and upon 

 examination the root is found to be either badly scarred or entirely 

 severed. (PI. IX.) This injury generally takes place between 1 and 

 4 inches below the surface. There are two general types of injury; 

 in one the taproot is cut off clean, and the beet wilts and dies (see 

 PI. X); in the other the wireworm, after eating into the root, turns 

 and descends, eating off a side of the root as it goes down (see 

 PI. IX). This, of course, scars the root badly, and if the beet is 

 quite young and tender it is apt to die. If, however, the beet is 

 quite strong and the root is swollen a little, so that the injury does 

 not cut off the sap sup{)ly, it will recover, though always remaining 

 distorted and undersized. (See PI. XI.) 



In years when the wireworms appear in numbers they are likely 

 to be concentrated in certain spots. When this occurs they kill 

 off all the beet plants in these areas, causing the characteristic 

 "bald si)ots." (Pis. XII-XV.) Wlien once they have collected in 



