EFFECT OF HUMIDITY ON WHITE FLY. 33 
ture and relative humidity. The relative humidity as taken at 
8 a. m. throughout the period of high temperatures and low humidity 
between the middle of June and August 20 averaged 52 per cent. 
The temperature during the same period ranged between an average 
maximum of 106° F. and an average minimum of 84° F. The 
average mean temperature was 95° F. So great was the effect of 
this hot, dry weather on the pupae of the white fly that they remained 
in a practically dormant condition throughout this interval, and 
many were killed by the penetrating rays of the sun. 
Lahore is situated in the plains about 50 to 100 miles from the 
Himalaya Mountains. Heavy rains falling in the outer ranges 
during the latter part of August affected the humidity of the sur- 
rounding plains. By August 20 the effect of these rains began to 
be felt at Lahore and was marked by a high rise in humidity over 
that of the preceding weeks, while the dry atmosphere changed to one 
of muggy oppressiveness. This humidity was accompanied by a slight 
lowering of the temperature. This condition continued for several 
days and on August 25 heavy showers fell. A very thorough examina- 
tion of the infested plants on August 26 showed that a remarkable 
change had taken place within the past few days. All living Aleyrodes 
were active, as noticed by exudations of honeydew, a condition not 
seen during the preceding several weeks of dry weather. The pupae 
were also changing to adults. This humid weather, accompanied by 
occasional showers, continued and by August 31 the first adult white 
flies emerged. By September 2 they could be seen in great numbers. 
The issuance of adult white flies was at its greatest height about 
September 7 or 8, while by September 13 practically all adults had 
emerged and eggs had been deposited very freely. 
The foregoing observations show that when dealing with high 
temperatures, such as in the Indian plains, humidity is the great 
factor regulating emergence of adult Aleyrodes. Low humidity 
coupled with high temperatures between the middle of June and the 
middle of August kept the pupae in a dormant condition. The 
approach of a humid atmosphere on August 20 and continuing into 
September effected immediate development of the white fly and rapid 
emergence followed. 
The effect of humidity on other insects was equally apparent. 
Several species of scale insects (Coccidae) which had been in a dormant 
condition throughout the summer commenced development with the 
approach of the humid period during the last of August. The rapidity 
of this development in the case of some species was most striking. 
Trees which had contained a moderate infestation of inactive scales 
during the summer months now became severely infested within a 
fortnight following the first rain. 
