Oct. 15, 1925 
Chloropicrin as a Fumigant for Cereal Products 
747 
Ten insects were placed in each sack and the sacks were suspended 
in the jars. The stopper was then removed from the small vial 
containing the dose wiiich had previously been measured out, and 
the chloropicrin was carefully sprinkled over the bottom of the jar. 
The vial was then dropped to the bottom of the jar and the glass 
cover put in place. 
The insects were watched carefully and the first sack of insects 
was withdrawn as soon as all movement had ceased. The remaining 
sacks were withdrawn in accordance with a schedule which was 
arranged on the basis of the time required for the movement to stop. 
As soon as a sack was withdrawn it was placed in the open air and 
left for a period of 48 hours, at the end of which time the per cent of 
dead insects in each sack was noted. As a rule, at least some of the 
insects revived in the sack which was first removed from the jar. 
Each successive sack usually had fewer survivors, until finally there 
were none. The time of exposure of the first sack in which there 
were no survivors was taken as the time required for 100 per cent 
kill for the concentration used in the experiment. In general, the 
decrease in the number of survivors was much more regular in the 
successive sacks when a high concentration was used than with a low 
concentration. The controls were left in sacks in the laboratory 
and were counted with the beetles from the experiments. 
The variation found when using some of the lower concentrations 
was often very confusing, and this may help to explain some of 
the discrepancies met with in the practical application of chloro¬ 
picrin. In one experiment there was a difference of more than 15 
per cent between two different sacks in the time required to kill 
100 per cent. Since no such irregularities were observed in the con¬ 
trols, these differences may have been due to certain sacks becoming 
wet with the chloropicrin when the dose was introduced, or to some of 
the insects closing their spiracles for a time when first put into the jar. 
The granary weevil, Calendra granaria L., was used in the experi¬ 
ments reported in this paper. Bertrand (3) used the rice weevil 
Calendra oryza L., but this species was not available during the 
present work, so the granary weevil, being very closely related and 
therefore assumed'to be comparable in susceptibility to chloropicrin, 
was chosen. The results are plotted in Figure 1. Time is recorded 
in minutes, and concentration in grams per cubic meter. The crosses 
represent the records of Bertrand (< 3 ), and the dots the results of the 
present work. Bertrand {5) states that the temperature varied 
between 20° and 27° C. during his experiments, while that in this 
present work varied between 22° and 24° C. The results are in 
general accord when it is considered that Bertrand had a variation 
of 7° in the temperature under which he worked. The inverse 
relationship between time and concentration seems to hold from the 
lowest to the highest concentration. 
Figure 2 shows the relationship of the time and temperature 
factors at a concentration of 20 grams per cubic meter. Again the 
dots represent the results of the present experiments, and the crosses 
those of Bertrand (6). It is clear that time, temperature, and 
concentration are important factors. -4 low value for any one may 
be compensated for by giving a correspondingly high value to one 
or more of the others. No relationship was found to exist between 
relative humidity and toxicity. 
