EFFECT OF HUMIDITY ON WHITE FLY. 33 



ture and relative humidity. The relative humidity as taken at 

 8 a. m. throughout tlie 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 plams. 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, wliiie 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 pupse 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 

 emiergence foUowed. 



The effect of humidity on other insects was equally apparent. 

 Several species of scale insects (Coccidse) 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. 



