THE TOBACCO BEETLE. iD) 
PHOTOTROPISM. 
Adults of the tobacco beetle are accustomed to darkness or semi- 
darkness. Up to a certain degree of intensity they respond positively 
toward light, but they are negatively phototropic if the ight is too 
intense. Observations made in tobacco warehouses and on beetles in 
specially constructed cages at the laboratory showed that they avoid 
intense sunlight, but. toward sunset, or when the light intensity is 
lowered, they move toward the source of light. 
REACTION TOWARD COLORED LIGHT. 
Laboratory experiments made with apparatus which transmitted 
light through color screens or ray filters which made it practically 
monochromatic showed conclusively that the tobacco beetle, in com- 
mon with other insects, reacts most strongly to colors of shortest 
wave length. The movement toward blue or blue-violet is most pro- 
nounced, and the movement toward red least of all. When a series 
of traps was operated with the light transmitted through color screens 
placed in regular order from red to violet the number of beetles at- 
tracted, in the majority of instances, increased in fairly regular order 
from red to violet. Experiments made with ele¢tric hghts showed 
that the beetles were attracted toward a bulb of clear glass transmit- 
ting light rich in rays of short wave length, and scarcely at all toward 
a bulb of red glass, which transmitted rays of long wave lene giving 
hight at the lower or red end of the spectrum. 
The adults, in common with other insects’ reacting negatively 
toward intense sunlight, are only slightly sensitive to light at the 
lower end of the spectrum, and rays of longer wave length, limited 
to red and orange, seem to act on them in much the same manner as 
darkness. Adults exposed to bright sunlight under color screens of 
red and blue were observed to collect under the red screen almost as 
readily as they did when an opaque screen was used in place of the 
red, although the apparent intensity of light under the two screens 
was the same. This shows a reaction directly opposite to that ob- 
served when the beetles, in darkness, are exposed to lights on low 
intensity. 
EFFECT OF TEMPERATURE ON ACTIVITY OF ADULTS. 
A series of laboratory experiments was conducted to ascertain the 
effect of ascending and descending temperatures on the activity of 
adults. Beetles were confined in the lower part of a long glass tube 
20 millimeters in diameter. A thermometer was passed through an 
opening in the cork and the tube lowered into an inverted bell jar filled 
with water. A support was arranged in.such a manner that the bell 
jar could be lowered into melting ice, or into a basin of water which 
