36 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



of the four classes given in Tahl(^ 111. It is proposed to show for each 

 locahty tlie ])r()portion of the total mortality due to each of the three 

 factors, a comparison of the mortality in each stage of the weevil — 

 larva, pupa, and adult— and the general climatic conditions ])revail- 

 ing during the period covered by the examinations. In this way it 

 may be possible to show whether any particular combination of cli- 

 matic conditions ])revailed in coincidence with the liighest })ercentages 

 of mortality found, or whether the ])ercentages may vary widely 

 under similar climatic conditions so tliat the real explanation for the 

 variation must be due to other causes than climatic differences. In 

 this table, as in Table III, the percentage of mortality in lan^al, pupal, 

 and arlult si acres is based upon the total numbers of those stages which 

 were' found alive or which had died from the effects of heat or drying. 

 It seemed impracticable to attempt the determination of the stage of 

 the weevil destroyed b}^ ants and parasites, though in many cases 

 it would have been possible. The "total of weevil stages found" 

 includes those found alive, those killed by heat or drying, and those 

 which had died but probably from some other cause than heat, and 

 each weevil cell emptied by ants as well as each instance of parasite 

 occurrence. 



In the column showing "total mortality from three causes'' it 

 ma}^ be seen that the range is from to 84 per cent, with the average 

 at 52 per cent. Eleven localities show a mortality above the average 

 and seventeen below it. For the eleven the average mortality is 

 63.2 per cent, while for the seventeen the average is but 34.2 per cent. 

 It is noticeable that nearly all of those showing the higher percentages 

 are located below or south of the center of cotton culture in Texas. 

 The figures in Table A^I show the conditions for mortality by these 

 three factors, and also give in each locahty and in a general way the 

 climatic conditions prevailing during the period of examination and 

 for ten or fifteen days previously. In cases where no records are 

 available, those are used for a near-by locality having weather con- 

 ditions probably similar to those of the locality in which the examina- 

 tions were made. The totals in this table show the general facts 

 concerning mortality under average conditions in the twenty-eight 

 localities representing in a general way the infested area. Besides 

 the comparison as to mortality by each of the three factors repre- 

 sented there is a general record showing the mortality found in each 

 stage of the weevil from heat or drying. The records of the four 

 principal classes of forms examined are combined in this table. 



It is shown that the mortality from heat in the larval stage amounts 

 to 52.6 per cent, in the pupal stage to IS per cent, and in the adult 

 stage to 6.3 per cent. Nearly 70 per cent of all the mortality caused 

 by heat or drying occurs, therefore, during the larval stage. An 

 early shedding of infested forms is plainly very desirable. 



