14 FARMERS' BULLETIN 848. 



weevils 11.5 per cent survived. As in the preceding case, these 

 weevils were placed under diverse conditions in different cages. These 

 conditions ranged from the most favorable to the least favorable; 

 that is, from an abundance of protection to practically none. The 

 sui'vival obtained was undoubtedl}^ very close to that occurring under 

 diverse natural conditions of that winter. It must be emphasized 

 that the winter of 1906-7 was abnormally warm. The average sur- 

 vival in experiments performed in Texas and Louisiana from 1906 to 

 1911 was 6 per cent, which must represent the average survival 

 occurring in nature. The enormous importance of still further reduc- 

 ing this percentage must be evident. 



Emergence from hibernation depends primarily upon temperatures 

 in the spring, although there are other minor factors concerned. 

 Generally, from the first to the middle of March the temperature has 

 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 hiberna- 

 tion is a prolonged process. 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 1st of July. 

 During each of these periods there was a comparatively short time — • 

 about 10 days, generally in May — of rapid emergence, preceded by 

 an initiatory movement and followed by a period during which the 

 number emerging day by day decreased with rapidit3^ 



HOW NATURE ASSISTS IN DESTROYING THE BOLL WEEVIL. 



Although the possible production of offspring in a single season by 

 one pair of weevils has been estimated at 12,755,100, as a matter of 

 fact natm-e has provided a number of agencies that serve to prevent 

 such excessive multiplication. The most conspicuous of these agen- 

 cies are heat and insects that prey upon the weevil. 



Effects ofli^at. — When infested squares faU to the ground they may 

 l)ecome so heated that the larvae are killed in a few minutes. The 

 insect in the larva stage can not leave the square, as it has no means 

 of locomotion whatever. Where the infested sc{uares are subjected 

 to the unobstructed rays of the sun the mortahty is very high. This 

 explains the M'ell-known fact that dry seasons are unfavorable to the 

 weevil, and indicates great difficulty in controlling the insects in 

 regions where precipitation is heavy. In Louisiana as many as 

 90 per cent of the immature weevils in cotton fields inspected have 

 been found to be destroyed tln-ough this agency. In Texas the 

 mortality from this cause is sometimes even higher. It was found, 

 from examinations in many quarters, that the extent of destruction 

 held a direct relation to the amount of shade. Wlien there was no 

 shade practically all of the larvje and pupae were killed outright. 



