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 writer was able in most instances 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 Aleyrodidse as well as with all Coccidae observed. 
Insects on the wing were seldom seen. In fact, this extremely hot, 
dry period appeared equally effective in checking the activity of 
insect life as does a prolonged cold period, such as occurs during the 
winter in central Florida or in the orange-growing parts of southern 
California. 
That vast numbers of insects are destroyed in 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 in holding the white fly in 
commercial control than all other factors combined. 
The Effect of Humidity on White-fly Development. 
It has been stated by Morrill and IjSack x 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 in the winter the rainfall during a normal year is confined to the 
so-called "monsoon period," occurring in June, July, and August 
iBul. 92, Bur. Ent., U. S. Dept. Agr., 1911. 
