August, '22] smith: Japanese beetle, larval food habits 309 



From the figures given it will be seen that from twenty-five larvae 

 approximately 84.0% by volume of the material eaten was vegetable 

 matter, and 64.3 per cent, of the total amount of material consumed 

 was from the roots of living plants. 



In an experiment started May 2, 1921, 200 three-ounce tin boxes 

 were filled with the following materials and one larva placed in each 

 tin. The object was to note the effect on the larvae, as shown by the 

 mortality, of the presence or absence of living plant roots in the soil. 

 Fifty tins were filled with rich sifted garden soil. Fifty tins were 

 filled with sifted subsoil taken at a depth of four feet, containing 1.45 

 per cent of organic matter. Fifty tins were filled with subsoil to which 

 was added pieces of partly decayed grass roots from which the soil 

 had been washed. Three weeks after the experiment was started the 

 tins were examined and the number of live and dead larvae were 

 noted. Replicate series were conducted in the autumn using young 

 larvae. The results obtained were similar. The following tabulated 

 data gives the results obtained. 



50 larvae placed in garden soil 



50 larvae placed in subsoil 



50 larvae placed in subsoil and decayed roots 



50 larvae placed in garden soil and fresh sod 



The data presented indicate that while the larvae may survive in 

 the soil for a certain length of time without living roots upon which 

 to feed, their presence is extrem.eh^ important to the development of 

 the grubs. This fact applies particularly to the sum^mer, early autumn 

 and spring, during w.hich periods most of the feeding is done. This 

 has also been borne out in our rearing cages where entire series have 

 died for no apparent reason other than starvation when sod was not 

 added to the soil. 



Summary 



In the past it was generally believed that the larvae of PopilUa 

 japonica fed largely on decaying organic matter in the soil. Observa- 

 tions made during the season of 1921 indicate that during the spring 

 and autumn, when most of the feeding is done, live plant tissues con- 

 stitute between 60 and 70 per cent of the food of the grubs. 



Injury has been noted to grass sod in pastures, golf courses, espe- 

 cially on the putting greens. In some places the grass was killed in 

 patches. It is probable that the most serious injury to grass land will 

 occur through the destruction of the finer rooted species, particularly 

 blue grass and red top. 



