RELATIONSHIP OF FACTORS OF CONTROL. 28 



but it is possible that they will gradually acquire an increasing 

 importance the longer the weevil remains abundant. 



There are other factors which are, or may become, of relatively 

 great importance in the fight against the weevil. Some of these have 

 been but slightly investigated. It is safe to assume that the factors 

 which have been mentioned include those which have thus far proved 

 to be of greatest importance in holding the weevil in check to some 

 extent. 



The relative value of these factors is certain to change suddenly, 

 and when one assumes a position of predominant influence the others 

 must undergo a readjustment of relative position. It is certain that 

 the efficiency of predaceous enemies and of parasites is gradually 

 increasing, while it is probable that the gradual adaptation of the 

 weevil to its new environment is rendering it more resistant, espe- 

 cially to the effects of the adverse climatic factors. Additional 

 observations of the effects of these opposing tendencies should bring 

 to light facts which will be of general significance in connection with 

 the study of many other pests besides the boll weevil. 



The area infested b}^ the boll weevil in the United States now 

 reaches a total of between 175,000 and 200,000 square miles. Of 

 course but a small percentage of this enormous acreage is actually 

 devoted to cotton culture, but the range in geological conditions is 

 naturally great. Thus in Texas cotton is cultivated extensively on 

 five or six very distinct geological areas each furnishing more or less 

 distinctive conditions of environment affecting faunal, floral, and 

 shelter conditions which may at any time prove to have an impor- 

 tant significance in the weevil status. 



INVESTIGATIONS SHOWING CONTROL BY HEAT, ANTS, AND 



PARASITES. 



Observations of the effect of various natural factors in controlling 

 the weevil have been accumulating since the beginning of the boll 

 weevil investigation. The earlier records, however, were not made 

 to include the simultaneous effect of several factors, and the records 

 presented in this connection are therefore confined to the observa- 

 tions made during 1906. 



Heat and drying are considered together, as their effects upon the 

 immature weevil stages are coincident and inseparable. The effi- 

 ciency of this factor naturally follows seasonal variations, but it is 

 largely affected by the distance between rows, the size of the plants 

 and density of their foliage, the season of occurrence in relation to 

 the state of the cotton crop, and by cultural conditions. 



Whenever ants are referred to in succeeding pages it should be 

 understood that no reference is intended to the Guatemalan "kelep" 

 (Ectatomma tuberculatum Oliv.), which has failed to maintain itself in 

 Texas. 



