August, '22] smith: Japanese beetle, larval food habits 305 



of doubtful value in this connection, because these materials them- 

 selves are mixtures of soaps and other materials, of which the soap alone 

 is toxic. 



Factors Influencing the Treatment 



The experimental results indicate that temperature is the limiting 

 factor in the use of this treatment. The best results are secured by 

 spraying when the insects are exposed to the sun during the heat of 

 the day. Under these conditions a consistent kill of 90% of the bee- 

 tles was obtained whereas simultaneous spraying of beetles in the 

 s.hade never resulted in more than 50% mortality. 



In applying the material the best results are secured by using a coarse 

 nozzle and sufficient pressure to thoroughly wet the foliage. 



The sodium and potassium soja-bean soaps are now selling at 8 to 9 

 cents per pound and at the present price of these materials it costs from 80 

 to 90 cents for 50 gallons of spray. 



The experimental work with these materials has been confined en- 

 tirely to field tests and observations and under the circumstances no 

 explanation can be offered at this time regarding the physiological 

 action of the material upon the insect. 



LARVAL FOOD HABITS OF THE JAPANESE BEETLE {POPILLIA 

 JAPONIC A NEWM.)i 



By LoREN B. Smith, Riverton, New Jersey 



For several years it was believed that the larvae of the Japanese 

 beetle fed largely on decaying vegetable matter in the soil.- 



Observations made during the present season indicate that while 

 a certain amount of humus and mineral matter passes through the 

 digestive tract, the larvae feed principally upon the living roots of 

 various plants. 



Field Observations 



During April and May, 1921, the writer observed the larvae actively 

 feeding on the roots of rye, clover, and several of the pasture grasses. 

 Further observations made in fields of rye disclosed the fact that in 

 nearly all cases the larvae were congregated about the roots of the 

 rye stools. The larvae have also been found feeding on the large 

 tap-roots of clover, some of which were nearly eaten through between 



^Published by permission of the Secretary of Agriculture of the U. S. Dept. of 

 Agriculture and New Jersey Dept. of Agriculture. 



^Davis, J. J. Green Japanese beetle. New Jersey State Department of Agri- 

 culture. Circular No. 30. p. 14. 1920. 



