70 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
tically all adults at this season emerge between 4 and 7 a. m. This is 
true both in the laboratory and in the grove. Of 233 white flies 
emerging separately in vials in the laboratory during August, 1907, 
212 emerged between 3.30 and 8 a. m., and the remaining 21, with 
one exception, emerged between 8 and 9.30 a. m. In the grove over 
95 per cent of the white flies emerge before 7 a. m. At this time of 
day the temperature ranges between 70° F. and 85° F. During the 
early spring, when the daily maximum temperature does not usually 
exceed 85°, emergence is not restricted to the early morning as during 
the heat of summer, but occurs at all times of the day. It may also 
be added that like conditions exist in October and November, but 
because of difference in seasonal history, they affect chiefly the spotted- 
wing white fly. 
EFFECT OF HUMIDITY ON EMERGENCE. 
Under normal Florida conditions at Orlando, at any season of the 
year, the relative humidity rises to nearly or quite 100 per cent by 
from 6 to 10 p. m., and there remains until about 6 a. m., when it 
normally drops rapidly, sometimes to as low as 19 per cent, though 
more often to from 35 to 60 per cent. It has already been stated that 
over 95 per cent of the white flies will have emerged before 7 a. m. or 
before the humidity has fallen far from the saturation point. That 
temperature and not humidity is the more important factor governing 
emergence in Florida, can be inferred by a comparison of the humidity 
and temperature records of Table XIII. It so happened that the 
cold wave of March 21, 1908, was accompanied by a higher average 
humidity, but the temperature and not the humidity prevented 
adults from emerging. Again, during the spring, when the daily 
maximum temperature is seldom above 85° — usually less — emergence 
goes on even at midday when the humidity has dropped to as low as 
33°. In this connection attention should be called to the fact that the 
humidity in the corked vials mentioned under the preceding heading 
remained at about 100 per cent throughout the greater part of the 
experiment. 
There are, however, times of abnormal weather conditions when 
lack of humidity seems to play an important part in preventing 
emergence. During the month of March there sometimes occur dry 
winds of several days' duration, accompanied by more or less heat, 
which seriously check emergence, and, as far as can be determined, 
cause many pupae from winch adults are about to emerge to die. 
Two such periods occurred during March, 1909, from the 3d to the 
6th, and from the 25th to the 27th, respectively. During these 
periods the relative humidity was extremely low, on one day dropping 
to 19 per cent. For 42 hours during the latter period the humidity 
ranged below 50 per cent and for 36 hours above 50 per cent. During 
