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 larvx (in soil balls) in wormseed-oil 
emulsion dip l 
Dosage (ascaridole per 6 liters of water) 
Percentage of larvae killed by immersion 
in dip for hours specified 
G 
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 larvae 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 larvae when no soil is 
present. This difference of six hours in the period of submergence 
necessary to kill the larvae 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 larvae 
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 larvae 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 larvae were warm or cold before or after being dipped, pro- 
vided the temperature of the dip itself was not lowered while the 
larvae were submerged. However, the immersion of la^ge 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 
» The Infestation of ins, phlox, sedum, etc., by Popillia japonic 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. 
I bese I wo 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. 
