THE CITRUS WHITE FLY: LIFE HISTORY AND HABITS. 71 
these periods emergence was noted to be seriously checked and at the 
end of the latter upward of 30 per cent of the pupse were dead, appar- 
ently from no other cause. 
EFFECT OF LIGHT ON EMEEGENCE. 
During the summer months light seems to have an influence on 
emergence. At this season emergence in the laboratory and grove 
begins at about daybreak. Observations made at hourly intervals 
on the emergence of 233 adults, from 3.30 and 4 a. m. show that white 
flies rarely emerge before this time. In one instance only about one- 
third as many white flies emerged from pupae kept in the dark as from 
those kept in the open, and their emergence was noticeably delayed. 
During the cooler months the low morning temperatures prevent the 
white flies from responding to this apparent stimulation due to light, 
and they emerge at various times after the temperature has risen 
sufficiently high. 
DURATION OF LIFE. 
Without food. — In none of the experiments conducted to determine 
the length of adult life without food have white flies lived longer than 
30 hours, and a very large percentage has died before the end of 24 
hours. When confined on leaves of plants other than those recognized 
as food plants, life is usually longer than this, but never approaches 
the normal length. White flies confined on crape myrtle in July died 
as soon as those kept in empty cages, but flies caged on oak, in March, 
lived as long as 4 days ; those on fig, in August, 3 days ; and on banana 
shrub, in July, 2 to 3 days. In all these tests flies were placed only 
on the tenderest growth. 
With food. — Adult life under normal outdoor conditions averages 
about 10 days, although individual white flies kept in cages have been 
known to live as long as 27 days. Adults are so fragile and so easily 
killed by winds and heavy showers and by numerous species of spiders 
and ants that their duration of life is at most very uncertain. Cage 
experiments during March, April, July, August, and September show 
that, in the cages at least, there is little difference in the length of 
life at various times of the year. 
The courtship of the citrus white fly has been observed to begin 
within 2 hours after emergence, and in one instance even before the 
wings of either male or female had become whitened. There is no 
time in the day when the males can not be seen courting the females. 
The male appears unable to locate the female at a distance much 
greater than one-fourth of an inch, according to Prof. H. A. Gossard. 
Observations made during the present investigations show that when 
males and females are placed in separate receptacles and separated 
