METHODS IN BOLL- WEEVIL INVESTIGATIONS. 113 



added improvement to this box as described, for some purposes, has 

 been made by Mr. Wihnon Newell, secretary of the Louisiana crop 

 pest commission, who has been cooperating with the Bureau of Ento- 

 mology in the fight against the boll weevil. It consists of a plate of 

 glass fitting smoothly upon a narrow projecting ledge formed by a 

 wooden strip tacked around the box on the inner side and near the top. 

 This allows the removal of the cover and facilitates inspection with- 

 out the danger of allowing the escajje of insects which have not 

 entered the tubes. 



Since its first advent into Texas there has been more or less specula- 

 tion as to how far north the weevil might be expected to spread. The 

 probable influence of the lower average temperatures encountered in 

 more northern latitudes also became a question of much importance. 

 To obtain a safe basis for forming conclusions upon many impor- 

 tant questions of this kind, it became necessary to secure much data 

 relative to temperature effects under conditions which could be kept 

 uniform and under the absolute control of the investigator. For 

 observations at temperatures ranging above the normal, a small-size 

 incubator has been found to answer well; such questions as those of 

 ventilation, humidity, etc., being carefully guarded. For tempera- 

 tures ranging below the normal ready-made apparatus can not be so 

 easily secured. Ordinary refrigerators may give temperatures as 

 low as 40° F., but their construction is not such as to allow of 

 approximate control of the temperatures intermediate between that 

 of the ice box and that of the outside atmosphere. To meet this 

 need it was found that a box must be built to order, and one was 

 designed having three compartments below the ice box in wdiich the 

 temperature could be varied at will in each compartment without" 

 affecting the others. Two compartments were dark, while the third 

 was lighted through double glass windows. When desired a ther- 

 mograph could be placed in any one of the compartments and an 

 accurate record obtained of the temperature prevailing for any- 

 desired period. The temperature above all compartments was kept 

 uniform by the retention of the water from the melting ice. With 

 the incubator and this ice box the development of the weevil could 

 be tested for any temperature, and from the periods found the total 

 effective temperature required to allow complete development at 

 any mean temperature could be quite accurately determined. This 

 w^ork led to the prediction that around Dallas, Tex., there would be 

 one less generation of the weevil than at Victoria, and such has since 

 been found to be the case. One of the most important results of this 

 work has been the demonstration that the number of generations, the 

 period in each developmental stage, and, in a general way, the destruc- 

 tiveness of an insect, can be thus determined for any new locality 

 31024— No. 60—06 m 8 



