SOME FACTORS IN THE NATURAL CONTROL OF THE 

 MEXICAN COTTON ROLL WEEVIL. 



INTRODUCTION. 



The natural control of the cotton boll weevil is so broad a subject, 

 comprising the effects of so many factors, some of which are imper- 

 fectly known and understood, that anything like a comprehensive 

 treatment of the subject is at present impossible. Doubtless many 

 factors of some importance have not yet been studied. Of the fact 

 that some factors do accomplish the destruction observed in indi- 

 vidual cases we have no doubt. From extensive series of such obser- 

 vations we may be able to reason safely as to the general tendency 

 of those factors, and we may possibly be able to assign to them a 

 relative value in their tendency to control under the conditions then 

 prevailing, but we must recognize the fact that all these factors, 

 however many there may be, are so interrelated and their influences 

 under varying conditions may so essentially differ that a study of 

 them becomes an exceedingly difficult problem. 



CONDITIONS REQUIRING CONSIDERATION. 



The magnitude of the work involved is directly increased by the 

 extent of the area affected and by the variations in climatic, geo- 

 logical, and cultural conditions which are encountered within the 

 weevil-infested area. While some factors may be studied through 

 multiplied observations as to their effect in individual cases, others 

 must be considered from the broader standpoints of the general 

 movement of the species, crop production, etc. 



Temperature and moisture conditions are undoubtedly the princi- 

 pal climatic factors which govern in a general way the distribution 

 of every species. Of these two factors, temperature is unques- 

 tionably the more important. The effect of this factor upon the 

 continued spread of the boll weevil has been a subject of interest 

 to entomologists ever since the weevil became a factor in the cultiva- 

 tion of cotton in Texas. It has been supposed that the weevil, 

 coining originally from a habitat much farther south, would finally 



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