INFLUENCE OF SOIL MOISTURE UPON THE RATE OF 

 INCREASE IN SUGAR-BEET ROOT-LOUSE COLONIES 



By J. R. Parker, 

 Assistant Entomologist, Montana Agricultural Experiment Station 



INTRODUCTION 



In a study of the sugar-beet root louse {Pemphigus hetae Doane) carried 

 on by the Montana Agricultural Experiment Station as an Adams project 

 since 1909, it was early recognized that soil moisture was an important 

 factor in controlling the rate of increase in root-louse colonies. By 

 means of general field observations, insectary experiments, and field 

 tests a considerable mass of data concerning this point has been col- 

 lected; and, because of their bearing on methods of control, they are now 

 published. 



GENERAL FIELD OBSERVATIONS 



Outside of the sugar-beet {Beta vulgaris) fields the subterranean form 

 of the root louse is most commonly found upon lamb's-quarters {Cheno- 

 podium album L.) growing in dry situations. The largest and most flour- 

 ishing colonies are to be found where this weed has pushed its way 

 through a ground covering of dry barnyard manure, pine needles, or 

 other material which provides a comparatively dry medium for the rami- 

 fication of the smaller rootlets. Lamb's-quarters growing in continuously 

 damp situations makes a larger and more succulent growth, but is rarely 

 heavily infested. 



In the sugar-beet fields it has been noted many times that root lice 

 are most abundant and that root-louse injury first appears where the 

 soil is the driest. A striking illustration of this was noticed in a large 

 sugar-beet field that was cut diagonally by a depression in which the 

 ground remained moist without irrigation the entire summer. When the 

 field was visited in October, there was a sharp line of demarcation be- 

 tween the moist soil of the depression and that of the general level of 

 the beet field, which at that time was quite dry. Sugar beets were 

 making a fine growth in the moist soil and not a root louse could be 

 found upon them, while in the drier soil around the borders of the depres- 

 sion nearly every sugar beet was very heavily infested. 



INSECTARY EXPERIMENTS 



In June, 191 1, insectary experiments were begun for the purpose of 

 determining the influence of moisture upon the rate of increase in sugar- 

 beet root-louse colonies. 



Journal of Agricultural Research, Vol. IV, No. 3 



Dept. of Agriculture, Washington, D. C. June 15, 1915 



Mont. — I 

 (241) 



