10 



BULLETIN 1332, U. S. DEPARTMENT OF AGRICULTURE 



present, it is confined to small amounts which can not be shaken out 

 or otherwise removed before treatment. The presence of this small 

 quantity of soil simply slows down the action of the wormseed-oil 

 emulsion dip and necessitates a longer period of dipping to secure 

 mortality of the larvae under these conditions than is the case when 

 the latter are entirely free from soil. 



Table 7. — Results obtained in dipping Popillia larvae (in soil balls) in wormseed-oil 



emulsion dip J 



Dosage (ascaridole per 6 liters of water) 



Percentage of larvae killed by immersion 

 in dip for hours specified 





6 



12 



15 



18 



24 





50 

 75 



100 

 100 



100 

 100 



100 

 100 



100 





100 







1 The larvae were immersed for the specified time at a temperature of 70° F. (21° C), and the percentage 

 of those killed is tabulated. A total of about 250 larva? were used in the tests on which this table is based. 



The results of dipping soil containing larvse are presented in Table 

 7. The method adopted in this phase of the work was as follows : 9 

 Fifty iris plants were thoroughly shaken and the soil thus removed 

 discarded. The plants were then cut to pieces and every vestige of 

 soil removed and saved. This was measured by volume and averaged 

 7 cubic centimeters per plant. Ten cubic centimeters of soil con- 

 taining a Popillia larva was wrapped in a small bag of muslin and the 

 bag tied at the throat with twine. A sufficient number of such bags, 

 each containing one larva, were used for the dipping tests the results 

 of which are presented in Table 7. It will be noted that the 1 cubic 

 centimeter ascaridole dosage was completely effective in 12 hours, 

 while twice this concentration did not decrease the period of dipping 

 necessary to secure a complete mortality. On the other hand, only 

 six hours of dipping are required for killing the larvse when no soil is 

 present. This difference of six hours in the period of submergence 

 necessary to kill the larvse when soil is present is due to the partial 

 soil absorption and consequent slowing up of the action of the toxic 

 material. Were large quantities of soil present not all the larvse 

 could be killed even with long-sustained dipping. In practice, there- 

 fore, the large clumps of iris are broken up into several smaller ones 

 and the greater bulk of the soil removed by thorough shaking. 



During much of the fall and spring shipping seasons for iris, phlox, 

 etc., the ground is cold. The question arose as to whether larvse in 

 this cold soil, when dipped, would be resistant to the insecticide. As 

 a result of a series of experiments on this point, it was found that no 

 difference in anything but the rapidity of killing resulted, whether the 

 soil and larvse were warm or cold before or after being dipped, pro- 

 vided the temperature of the dip itself was not lowered while the 

 larvse were submerged. However, the immersion of large quantities 

 of cold soil or plants in the- dip appreciably lowers its temperature 

 and thereby reduces its toxicity. For this reason it is advisable to 



8 The infestation of iris, phlox, sedum, etc., by Popillia japonica in the infested area at the present time is 

 light, not more than 5 to 10 per cent of the plants being infested. Further, these plants are expensive. 

 These two facts render it almost impossible to obtain the preliminary data by natural means, since the pro- 

 cedure would involve the use and destruction (by cutting) of thousands of plants. The method here 

 described was therefore adopted and the results checked and confirmed by the dipping of several thousand 

 plants and their examination to determine the effect of the toxic material upon the larvae present. 



