15 
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- 
cles that serve to prevent such excessive multiplication. The most 
conspicuous of these agencies are heat and insects that prey upon the 
weevil. 
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 this stage can not leave the square, as it has no means 
of locomotion whatever. Where the infested squares are subjected 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 have 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 pupz 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. A parasite instead of a boll weevil 
emerges from the injured fruit. Special studies on these parasites 
have led to many suggestions for practical control. Moreover, the 
parasites seem naturally to be increasing in numbers and effective- 
ness against the boll weevil. In one instance in 1907 the mortality 
due to parasites in a field near Robson, La., was 77 per cent. About 
the same time 61 per cent of the weevils in a certain field 
near Victoria, Tex., were killed by parasites. These enemies of 
the weevil have existed in the country for an indefinite time. Their 
natural habit has been to prey upon weevils more or less related to 
the boll weevil that have occurred in this country for many years. 
They never feed on vegetation. It is undoubtedly true that they are 
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