62 THE SUGAR-BEET WIREWORM. 



wore bein<]j collocted. It was suggested also by the different states 

 of affairs noted in different fields where various systems of culture 

 had l)een })racticed. These observations were carefully made in 

 fields aggregating over 600 acres, and daily during a period covering 

 about two months. 



Two different methods are practiced by the growere in disposing 

 of the beet to})s winch remain in the field (see PI. XX) after the crop 

 has been harvested. Some growers leave them in the field to be 

 ])lowed under and act as a fertilizer, while others use them for stock 

 feed. In the latter method, which may be spoken of as clean culture, 

 the beet to})s are either disposed of by ])asture (PL XXI) or they are 

 hauled from the field (PI. XXII). The tops are removed best by 

 pasturing either vdilx cattle or sheep. 



The tops which are left for fertilizer are supposed to be plowed 

 under, but by the time the land has been harrowed several times, and 

 planted, not a few have reappeared on the surface. Then as the 

 beetles appear in the spring and enter their secondary hibernation 

 they find excellent shelter and feeding places (see PI. XIX, fig. 2), and 

 most of them remain in the field near the place where they emerged 

 and are able to pass this critical period of their lives safely. On the 

 other hand, where the tops and old beets have been cleared off, the 

 beetles find no place to hide, and consequently move to other fields 

 in search of shelter. Very few can hide under clods or in the soil on 

 account of intermittent rains. 



One iUustration of the effects resulting when beets are left in the 

 fields Nvill ])e sufficient, for this same state of affairs was found to 

 exist in all the fields examined. 



The beet fields .1, B, and C adjoined one another as shown in the 

 diagram (fig. 9). At the right of (7 was a field of alfalfa. In A the 

 beet tops had been left in the field to act as a fertihzer; in B and C 

 they liad ]>een cleared off. During the preceding year the field C 

 ha(i suffered from mreworm injury as much, if not more, than any 

 field in the Compton district. On this account there must have been 

 many mature wireworms there, and consequently many beetles 

 emerging, yet when the beetles were collected in these fields hardly 

 any were found in B and C, and they were taken in A literally by 

 thousands. As an experiment, a})Out oO old beets were scattered in 

 the field C, along the line c c. These beets were inspected daily from 

 this time on, and found to shelter large mmibers of adults, even though 

 none had been taken previously in C. Conditions in the other two 

 fields remained as before, no beetles, or very few, being found in B 

 while A "yielded its usual number. 



A simple conclusion can be drawn from these observations. The 

 beetles collected only where they could find shelter, and those which 

 emerged from perfectly clean fields had either to move to other fields 



