135 



for the normal activities and development of the weevil. Affecting 

 one in the same direction as the other, the pest is, therefore, enabled 

 to very closely keep pace with its food supply under all kinds of 

 natural conditions. 



The most favorable conditions for the weevil are a high temperature 

 and abundant moisture throughout a long season. These conditions 

 favor the growth of the plant and produce a very large number of 

 squares, which supply abundant opportunity for the rapid multiplica- 

 tion of the weevils. Severe drought checks together the growth of 

 the plant and the development of the weevils. It has not yet been 

 determined whether the death of larvae in fallen squares exposed 

 directly to the rays of the sun is due principally to the heat produced 

 or to the complete drying of the food supply. It is certain, however, 

 that one or both of these factors produce a considerable mortality 

 among the larvae and pupae so exposed during long-continued hot and 

 diy weather occurring before the plants have become large enough to 

 shade most of the ground. After that the shade produced prevents 

 most of the good work of the sun in destroying weevils. 



TEMPERATURE ENDURED BY WEEVIL LARV.E IN SQUARES EXPOSED TO 



SUNSHINE. 



During the middle of August, 1901, at which time it was expected 

 that the maximum temperature for the summer would be obtained, 

 over 500 squares were spread upon bare ground where fully exposed 

 to direct sunshine. During part of these tests the thermometric read- 

 ings were furnished by a maximum thermometer so wrapped with 

 leaves as to give the mercury about the same protection from the 

 sun as was had by larvae in squares. In another part of the test a 

 thermograph was properly adjusted and so placed as to record the 

 temperature prevailing at the surface of the ground. The results of 

 these tests appear in the following table: 



Table XXXVII. — Temperature endured by young stages in squares. 



Lot No. 



Number 



of 

 squares 

 tested. 



Maximum 

 degree 

 of heat. 



Number 



of 

 weevils 

 devel- 

 oped. 



Percentage 

 of total 

 squares 



developing 

 weevils. 



Percentage 



of total 



squares 



showing 



mortality. 



Percentage 

 of squares 

 showing 

 weevil de- 

 velopment 

 becoming 

 adult. 



Percentage 

 of squares 

 showing 

 weevil de- 

 velopment 

 found 

 dead. 



1 



25 

 25 

 25 

 25 

 25 

 100 

 100 

 100 

 100 



°F. 

 117 

 120 

 117 

 120 

 117 

 119 

 119 

 118 

 118 



7 



10 

 11 



5 



5 

 20 



43 



28 

 40 

 44 

 20 

 20 

 20 

 43 





 8 

 

 

 

 3 

 1 

 6 

 2 



100 

 83 

 100 

 100 

 100 

 87 

 98 

 91 

 97 







2 



17 



3 







4 







5 







6 „ 



13 





2 



8 



61 61 



59 | 59 



9 



9 



3 







Total 



525 





221 







1 



Average 



118 







43 



3 



94 6 













