EFFECT OF HUMIDITY ON WHITE FLY. 31 



If large leaves grew in this part of the tree their examination was 

 usually certain to reveal living insects provided the latter were to be 

 found on the tree. In fact, after extended experience in the examina- 

 tion of citrus trees in India, examination of the larger leaves near the 

 trunk of a tree was found to be such a conclusive key to infestation 

 that the wTiter was able in most uistances to "size up" the infested 

 leaves before starting the inspection. 



The statements previously made show the destructive action of 

 very high temperatures on the citrus white fly. The prolonged hot, 

 dry summer weather of the plains of northern India checks the 

 development of almost all terrestrial forms of insect life. During the 

 months of July and August, 1911, not only was the development of 

 the white fly at a standstill, but this condition was also noticeable 

 with other species of Aleyrodidge as well as with all Coccidse observed. 

 Insects on the wing were seldom seen. In fact, this extremely hot, 

 dry period appeared equally effective in checking the activity of 

 insect Hfe as does a prolonged cold period, such as occurs durmg the 

 winter in central Florida or in the orange-growing parts of southern 

 California. 



That vast numbers of insects are destroyed m these regions of 

 greatest heat is at once apparent to the entomologist who has spent 

 a summer in India. In summing up the writer's experiences and 

 observations he is led to the belief that this hot, dry climate of the 

 Indian plains exerts a greater influence m holding the v/hite fly in 

 commercial control than all oth^r factors combined. 



The Effect of Humidity on White-fly Development. 



It has been stated by Morrill and Back ^ that "while a normal 

 amount of humidity is necessary for emergence of the white fly 

 to occur, it is not so controlling a factor as temperature during 

 ordinary Florida weather." We have found that the above state- 

 ment will have to be modified if applied to the Punjab of India, and 

 this is not surprising when it is considered that the normal humidity 

 and temperature of these two countries are so essentially different. 



Under normal conditions at Orlando, Fla., the relative humidity at 

 any season of the year rises to nearly or quite 100 per cent by 6 to 10 

 p. m., and remains at this degree of humidity until the following 

 morning. Rain falls throughout the year, but is lightest during the 

 winter months. 



In the Punjab it was found that the humidity is comparatively 

 low throughout the year. With the exception of a few light falls of 

 rain m the winter the rainfall during a normal year is confined to the 

 so-called ''monsoon period," occurring in June, July, and August 



I Bui. 92, Bur. Ent., U. S. Dept. Agr., 1911. 



