THE BOLL WEEVIL PROBLEM. 15 
become high enough to cause weevils to begin to emerge. Naturally, 
the individuals under the heaviest protection are affected latest by 
the temperature. The consequence is that emergence from hibernat- 
ing is a prolonged operation. During one season (1906) it extended 
from the middle of March to the 28th of June; during another season 
(1907) from the middle of February to about the first of July. 
During each of these periods there was a comparatively short time 
about 10 days—of rapid emergence, preceded by an initiatory move- 
ment and followed by a period during which the number emerging 
day by day decreased with rapidity. 
HOW NATURE ASSISTS IN DESTROYING THE BOLL WEEVIL. 
In the preceding paragraph attention was called to the possible 
production of 12,755,100 offspring in a single season by one pair of 
weevils. As a matter of fact, nature has provided a number of agen- 
cies that serve to prevent such excessive multiplication. The most 
conspicuous of these agencies are heat and insects that prey upon the 
weevil. E 
Effects of heat—When infested squares fall to the ground they 
may become so heated that the larvee are killed in a very few minutes. 
The insect in the larval stage can not leave the square, as it has no 
means of locomotion whatever. Where the infested squares are sub- 
jected to the unobstructed rays of the sun the mortality is very high. 
This explains the well-known fact that dry seasons are unfavorable to 
the weevil, and indicates great difficulty in controlling the insects in 
regions where the precipitation is heavy. The more rankly the plants 
grow and the more the ground is shaded, the less effect in weevil con- 
trol can be expected from heat. Nevertheless, in many cases in Texas 
the enormous total of 40 per cent of all the immature weevils in cot- 
ton fields inspected has been found to be destroyed through this 
agency. It was also found, from examinations in many quarters, that 
the extent of destruction held a direct relation to the amount of shade. 
When there was no shade practically all of the larve and pupx were 
killed outright. Some of the important means of control, to be de- 
scribed later, are based upon this consideration. 
Insect parasites.—The second of the important agencies provided by 
nature for the control of the weevil is a large number of predaceous 
insect enemies. These consist of a variety of forms which prey upon 
the boll weevil. Forty-five species of these enemies are known. Of 
these, 23 are parasites, which by means of their ovipositors place eggs 
on the immature stages of the weevil within the square or boll. The 
young of the parasite develops by feeding upon the immature boll 
weevil, which it ultimately kills. Thus a parasite instead of a boll 
weevil emerges from the injured fruit. Special studies on these para- 
512 
