32 BULLETIN 926, U. S. DEPARTMENT OF AGRICULTURE. 



transpiration of the plant further lowers the temperature surround- 

 ing the developing weevil, and for 12 of the 24 hours of the day the 

 minimum temperatures below 84° F. are retarding and prolonging the 

 developmental period. After the infested square drops off the plant 

 it is exposed to the high soil temperatures which range well above 

 100° F. from 10 a. m. to 5 p. m. The immature weevil is again re- 

 tarded and all temperatures above 84° F. as well as below 84° F. 

 act as retarding factors. 



THE DEVELOPMENTAL PERIOD OF THE BOLL WEEVIL ON DIF- 

 FERENT TYPES OF SOIL. 



Although the field biology of the boll weevil has not been studied 

 for the different types of soil, the results secured at Madison, Fla., 

 indicate certain generalizations which will probably hold good for 

 the majority of cases. 



In addition to heat and dryness soil drainage must be considered. 

 Poorly drained soils such as are found in the Mississippi Delta and 

 the swamps and river bottoms will probably show an average period 

 of development from egg to adult to be a few days shorter than it 

 would be were these soils well drained. On the other hand sandy, well- 

 drained soils, such as the Gulf Coastal Plains, the oak, .hickory, and 

 pine uplands, and the rocky hillside types, will probably show a longer 

 period of development than any other generalized type of soil. The 

 semiarid region of Texas should show the longest period of weevil 

 development under field conditions. The range in the develop- 

 mental period at Madison, Fla., was from 16 to 38 days for weevils 

 developing in squares and it appears probable that the maximum 

 period would be much greater in the dry regions of Texas. 



THE EFFECT OF THE DETERMINATE GROWTH OF THE COTTON 

 PLANT ON THE BIOLOGY OF THE BOLL WEEVIL. 



Perhaps no single factor contributes so much to the control of the 

 weevil as the determinate growth of the cotton plant. On the Gulf 

 Coastal Plains type of soil at Madison, Fla., the upland cotton 

 usually sets its crop by the 20th of July and the cotton is practically 

 all open by the 20th of August. In addition, the cotton plants are 

 usually attacked by several species of rusts and wilts, which result 

 in the plant becoming decadent, shedding off the leaves, squares, and 

 immature bolls. This leaves the weevil with few breeding places. 

 At this particular time also the weevils are so numerous in the cotton 

 fields that the few squares growing on the plants are subjected to an 

 overwhelming attack for both food and breeding purposes, which 

 results disastrously to the fall generations of the boll weevil. The 

 adult weevils in the field rapidly die off, and as few weevils are 



