THE CoNFUSED FLoUR BEETLE 79 
In consideration of the first proposition, various flours were 
placed in cylindrical jars with removable partitions, which divided the 
jars into five equal sectors. [qual amounts of the five cereals to be 
used in the experiment were placed in the various sectors of the jar 
and the partitions were removed. The surface was then made as 
smooth as possible without packing the cereal and a small depression 
was formed in the center. The jars used were 10.5 cm. in diameter 
and the cereal was about three cm. in depth, except in Series 3 as 
recorded below. The beetles were placed in the depression in the 
center of the jar and, being thus surrounded by equal parts of the five 
different cereals, they were free to express their choice. 
The experiments were carried out in the dark in order to eliminate 
light as a factor. The duration of the experiments varied from a few 
hours to several days, the length of time making little difference after 
the first few hours when the insects were exploring about. When the 
time between examinations extended into weeks another factor entered 
in, as will be shown later. Observations were made by replacing the 
partitions and removing the different foods to count the number of 
insects contained in them. When one hundred insects were used, the 
number found in any one flour would be the percentage of relative sus- 
ceptibility of that flour as compared with the other flours used in the 
experiment. In making the counts, beetles which remained in the center 
and expressed no choice were disregarded. Consequently the figures 
given for the counts do not always total one hundred. In all cases 
where the average percentage is given the actual percentage of the 
beetles which did express a choice has been computed. 
The relative susceptibility of five grades of wheat flour was 
studied in this way. [Fach series of experiments was performed with 
a different lot of beetles. The following results are the averages for 
each of the five series. 
EXPERIMENTS WitH ApuLt Tribolium Confusum 
Series 1 Series 2 Series 38 Series 4 Series 5 
Average of Average of Average of Average of Average of 
Flour Scounts 5counts 6counts 3 counts 3 counts 
per cent per cent percent percent per cent 
Binst muddilings i... . 12.092 17.504 ese 11.734 112733 
Irie GANGS ss oce0case 12.092 10.914 6.52 14.064 14.063 
First low grade .:..... 17.812 9.804 1.92 13.734 15.20 
IDES TAMbIMES sis soc coe 20.672 14.204 1.92 17.064 16.330 
Biraiiipe se teebay seis oem 37.332 47.514 82.320 43.404 43.730 
These flours vary in refinement from the fine middlings to the 
bran. In Series 3 the materials were only 1 cm. in depth, which may 
account for the difference of percentages. 
