86 INSECT ENEMIES OP THE BOLL WEEVIL. 



The figures show that parasitism becomes very high under favor- 

 able conchtions and also that agriculture mocUfies the insect control. 

 Obviously therefore those agricultural methods which will favor the 

 highest insect control must be sought. These methods, as now 

 known, will be dealt with more fully in a following section. 



It was feared for a long time that the parasites of the weevil would 

 be held in control by the warm climatic conditions which affect the 

 boll weevil. This is not so. We have found abundant proofs of the 

 fact that a temperature which will kill the boll-weevil larva will not 

 kill the egg or small parasite larva in the same cell, and that the 

 parasites can develop to maturity on the cMed remains of the weevil. 

 The temperature fatal to the boll weevil is 123° F., a temperature 

 frequently reached on a hot burning soil. We have found in several 

 years that a low temperature which will kill the boll-weevil larva is 

 also not fatal to the parasites, for in November, 1907, when 97 per 

 cent of all the boll-weevil stages were frozen, no evidence whatever 

 could be found of mortality among the parasites. The minimum 

 fatal temperature of the boll weevil is 12° F. 



3^. INTERPRETATION OF THE BIOLOGICAL COMPLEX. 



The complicated biological factors which have been noted in Part II 

 have been summarized briefly in section 16 of that part (p. 82). 

 The interpretation of these facts has been suggested in a number of 

 places throughout the second part. Hence only a few words are 

 necessary at this point. 



The fact that surrounding each cotton field there are numerous 

 plants harbormg weevils and their parasites is of extreme importance 

 in this problem. These parasites are generally capable of attacldng 

 the boll weevil under conditions of necessity or alternative choice. 

 The aim is therefore to find all the methods by which these parasites 

 may be forced to leave their native hosts and attack the boll weevil. 

 In fact, the entire second part has been devoted to giving these facts 

 in order to bring out this single point. 



4. now TO PROFIT BY EXISTING CONDITIONS. 



COLLECTION OF COTTON SQUARES IN SCREENED CAGES. 



As has just been pointed out, there are conditions around the cotton 

 fields which are potential of a considerable increase in the parasitic 

 control of the boll wee%'il. Probably no other method will yield 

 better results than the gathering of the cotton squares wliicli are 

 infested and placing them in wire-screen cages of 16 or 18 mesh to 

 the inch and placing these cages in selected parts of the cotton 

 fields. This method is not new in entomological practice. It has 



