242 Journal of Agricultural Research voi. iv. no. 3 



Sugar-beet plants 3 inches in height were transplanted singly into 

 8-inch pots. After they had started to make a new growth, the earth was 

 pushed away from a portion of the taproot and eight small lice in the 

 first instar and two adults were placed upon each plant. Thirty plants 

 were infested in this manner. 



They were divided into three lots and watered as follows: Lot i, sub- 

 irrigated every other day from June 15 to August 15; lot 2, subirrigated 

 every day from June 15 to August 15; lot 3, watered from above every 

 day from June 15 to August 15. So far as practicable, the water applied 

 any one day was the same in amount for all plants, but, because of the 

 unequal moisture-retaining capacity of the soil in different pots, this 

 was not always advisable. In general, no plants were kept wet enough 

 to seriously retard their growth, and none were allowed to suffer for lack 

 of moisture. All of the pots were set in large saucers, and, where the 

 plants were subirrigated, the water was poured into the saucer and taken 

 up by the plant as needed. On August 15 the soil in each pot was 

 minutely examined, and all root lice that could be recovered were counted. 



The data obtained are shown in Table I. 



Table I. — Record of sugar-beet root-louse increase under different soil-moisture conditions. 



First insectary experiment 



Upon plants subirrigated every day 100 root lice increased to 1,760 in 

 two months. Upon plants receiving the same amount of water from 

 above 100 root lice increased to only 214 in the same length of time. 

 This decided difference was probably due to the fact that in the subirri- 

 gated pots the soil was comparatively dry to a depth of several inches 

 below the surface. It was from this drier soil that most of the root lice 

 were recovered. Where the water was added from above, the soil was 

 soaked throughout each day, apparently bringing about conditions 

 very unfavorable to root -louse increase. 



Upon plants subirrigated every other day 100 root lice increased to 

 4,554 in two months. By far the greatest number of lice was produced 

 upon the sugar beets grown under the driest conditions. 



In January, 1912, practically the same experiment was repeated, the 

 only difference being that instead of applying a certain amount of water 

 on certain days water was applied whenever necessary to maintain the 

 soil conditions desired. Thirty plants, infested as before, were divided 



