INFLUENCE OF CLIMATIC CONDITIONS KSPKCIALLV. 48 



that in (iroiip A aiul a total rainfall for each moiilh a\ crauniiL'' ■>.7') 

 inches, which is 1.9:2 a])ov(' the normal, there is a total nuntalitN fiom 

 all three causes av(M-aii:iHiij: hut 19.1 ])er cent . while that from licat aloiic 

 averages hut 7.1 per cent. A comj)aiison of the moj"talit\- from aiit 

 work })et\veen (Iroups A and C shows in (' a dccicasc which is vcrv 

 nearly ])roportional to that found for heat, while th(> reduction in 

 parasite work is comj)aratively sliulit. 



These facts sccmu to point to tlu^ conclusion that other factors than 

 clin^r.tic conditions nuist explain tlu* variations in mortality which 

 are sliown in this table. ITndoubtedly extnnic variations in tempera- 

 ture and rainfall are exceechni^ly important; hut it is obvious that the 

 airragc variation in tli(vse factors does not produce* a correspondinir 

 variation in the mortality figures, such as niiii;ht l)e ex|)ecte(l. \\\'i- 

 dently there are other factors modifying or ncMitrali/ing the cMeet of 

 climatic variations, which if acting alone miglit ])r()(luce more consist- 

 ent results. 



INFLUENCE OF CULTURAL CONDITIONS. 



High teni})erature can affect the weevil stages only after the forms 

 have fallen or been so cut off from vital connection with the plant 

 that the sap flow is stopped and a clrying of the form results. 'i1i(» 

 efl'ect upon the weevil stage will. then depend upon the conditions of 

 exposure to the heat. If the square or boll remains hanging or dries 

 upon the plant, the temperature in it will not rise as high as if those 

 fonns were exposed directly to sunshine upon the surface of the 

 ground. If the square or boll falls to the ground, its position in 

 regard to the shade of the plant will determine largely the degree of 

 exposure to the heat of the sun and, consequently, the probability as to 

 the survival or destruction of an inclosed weevil stage. The direction 

 in which the rows run, and more especially the open distance between 

 plants, will aflect the exposure of the fallen forms to the direct action 

 of the sun. The dryness of the surface soil is another factor wliicli 

 will largely affect the drv^ng of the forms and the mortality resulting 

 from heat. The work of the living larva3 naturall}^ produces a larger 

 degree of moisture in the infested forms than wdll be found in those 

 which contain no weevil stage. If the conditions are such as to 

 insure a very rapid and complete drying of the form within a. few days 

 after it falls to the ground, there is a strong probability that the 

 weevil stages affected will be destroyed by heat or drying. If climatic 

 or environmental conditions favor the weevil's development until the 

 pupal stage is reached, the condition of the f()rm is then much mor(* 

 favorable for the entrance and attack of the ants. The ants seem 

 to be able to recognize the presence of a living weevil stage within 

 a form and rarely, if ever, enter forms in which the stages ]ia\e j)re- 

 viously been destroyed by heat. If ants destroyed both parasite and 

 weevil stages no evidence of the parasitism might remain. It is 



