PSC EE. 
THE RELATION OF SEX TO HELIOTROPISM IN THE BROWN-TAIL 
MOTH.' 
BY WILLIAM REIFF, HARVARD UNIVERSITY. 
For the purpose of obtaining statistical data concerning the attractive power of 
electric light for the various orders of insects, during the spring of 1909 we had built 
upon the grounds of the Bussey Institution a light trap of large dimensions. A more 
detailed description of this trap will be given later after I have been able to gather 
together for publication the data concerning the various material collected, but for 
the present it will suffice to state that the source of light was an arc light consuming 
a current of seven and a half amperes. The light was burned regularly each evening 
from sunset until two hours before sunrise. : 
In connection with the amount of brown-tail moth material obtained it should 
be mentioned that all nests in the neighborhood of the Institution had been carefully 
removed during the spring so that the moths could not be present in abundance. 
The daily weather conditions were noted shortly after sunset. The results are in- 
dicated in the table on p. 116. 
We can see from the table that during the first twelve days, only a single female 
flew to the light. During this time we had either moonlight nights, or when it was 
cloudy, an abnormally low temperature for this time of the year; then as the moon- 
light decreased and the temperature rose, a few females were attracted. ‘The un- 
usually warm 13th of June brought large numbers of both sexes on a night of feeble 
moonlight. While males of the brown-tail moth had appeared more or less regularly 
on all other days during the flying time, no females came when the temperature sank 
below 19° C. The proportionate numbérs of the two sexes on the same days were 
extremely variable. An unusually warm night undoubtedly has the greatest influence 
in attracting both sexes to the electric light, but if there should be at the same time 
a very noticeable moonlight the number of females will remain far below that of 
1Contributions from the Entomological Laboratory of the Bussey Institution, Harvard University, 
No. 10. 
115 
