300 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



usually employed, there seems reason to believe that the use of 

 arsenate of lead at heavier doses than commonly recommended will 

 kill from 50 to 60 per cent of the beetles. Other stomach poisons 

 are under investigation, -especially metallic cyanids, such as nickel 

 and copper. Attention is also being given to organic chemicals in 

 the hope that a substitute for arsenical insecticides may l)e found. 

 Contact insecticides against the achdts have been experimented with 

 for several seasons, and it has been found that a contact insecticide 

 of sodium-soy bean soap will kill approximately 90 per cent of the 

 beetles. Fortunately this soa}) can be used on practically all types 

 of foliage attacked without injurious results. 



Additional studies have been made of possible methods of destroy- 

 ing the Japanese beetle grubs in the soil. Paradichlorobenzene 

 probably gave the best results against the larvae in sod. When used 

 at the rate of 300 pounds per acre at a depth of approximately 1 

 inch, with the drills 4 inches apart, it killed approximately 75 per 

 cent of the grubs. Tlie cost of such treatment is high, and addi- 

 tional studies are being made. Greenhouse soil has been the sub- 

 ject of special investigation, in view of the necessity of grub-free 

 soil for iDotting purposes in order to avoid danger of dissemination 

 of the grubs in the shipment of potted plants. It was found that 

 carbon disulpliid is a cheap and efficient material for fumigating 

 potting soil. For best results not less than 1 pound to a cubic yard 

 of soil must be used, with an exposure of 48 hours at a temperature 

 above 50° F. Soil up to almost any quantity may be treated by this 

 method with assurance that the grubs will be killed. Thorough- 

 going experiments to determine the possibility of vacuum and pres- 

 sure for the destruction of the grubs in the soil have not shown 

 favorable results. Tests of various arsenicals as soil insecticides are 

 under way. Arsenate of lead has proved to be the best and will 

 kill the grubs. Plants vary in their resistance to this treatment 

 and further studies are necessary. 



A paper giving detailed information on the feeding habits of the 

 beetle has been prepared for publication, as well as a paper on the 

 feeding habits of the larva. It appears that the insect is changing 

 its habits somewhat from season to season in its new environment. 

 This is especially true of the adult beetle. During the season of 

 1922 the beetles were excessively abundant in the territory infested 

 3 and 4 years ago, attacking peaches, apples, grapes, and many other 

 plants, including certain shade trees. There is nothing to indicate 

 that the insect has reached its limit of capabilities in this respect. 



Studies are in progress to determine the possibilities of destroy- 

 ing the grubs in the soil by cultural practices as carried out in farm- 

 ing and trucking operations. 



Suitable equipment has been obtained for making a detailed study 

 of the effect of the removal of the soil from " balled earth " nursery 

 stock, such as conifers. Unless satisfactory methods can be found 

 to kill the grubs under these conditions, nursery interests will suf- 

 fer, as it would not be safe to ship balled-earth plants. 



The search for parasites of the Japanese beetle in Japan has been 

 vigorously prosecuted. 



Some 125,000 Japanese beetles infested with a tachinid parasite 

 have been collected in Japan and forwarded to the Riverton, N. J., 



