BIOLOGY OF THE MEXICAN COTTON BOLL WEEVIL. 31 



TEMPERATURES FATAL TO THE IMMATURE STAGES OF THE BOLL WEEVIL 



Owing to the lack of proper soil thermometers, it was impossible 

 to determine accurately the fatal temperatures for the immature 

 stages of the weevil. The thermometers in use frequently recorded 

 maximums of 115 to 125° F., and under these maximum soil tem- 

 peratures it seems safe to assume that not more than 10 per cent of 

 the immature weevils will survive on Norfolk sandy soils such as 

 occur at Madison, Fla. 



THE EFFECT OF TEMPERATURE ON THE LENGTH OF THE DEVELOPMENTAL 

 PERIOD OF THE IMMATURE STAGES OF THE BOLL WEEVIL. 



Mean temperature and humidity either shorten or prolong the de- 

 velopmental period of the immature weevil. The exact amount of 

 humidity required for development under optimum conditions has 

 never been determined. A mean temperature of 84° F. has been de- 

 termined as the optimum temperature for development of the im- 

 mature weevil stages. Were it possible for the immature weevil to 

 have the exact amount of humidity and a mean temperature of 84°. 

 the developmental period of the immature stages would be approxi- 

 mately 8 days. Temperature and humidity, however, are never just 

 in the right proportion and so the period of development varies under 

 different conditions. 



THE EFFECT OF TEMPERATURE ON THE LENGTH OF THE DEVELOPMENTAL 

 PERIOD UNDER INSECTARY CONDITIONS. 



Under insectary conditions the development of the weevil has been 

 shown to be approximately 14.3 days from egg to adult. This period 

 of development is much shorter than the period under field condi- 

 tions owing to the smaller variation in extremes of temperature. 

 The mean temperature at Madison, Fla., under insectary conditions 

 during the months of June, July, and August approximates 81° F. 

 according to the United States Weather Bureau records. The aver- 

 age mean temperature is lower by 3° than is required for the optimum 

 developmental conditions. Therefore it is to be expected that the 

 developmental period would be approximately 14 days under in- 

 sectary conditions. 



THE EFFECT OF TEMPERATURE ON THE DEVELOPMENT OF THE IMMATURE 

 STAGES OF THE WEEVIL UNDER FIELD CONDITIONS. 



Under field conditions the development of the immature weevil is 

 considerably retarded and prolonged. It has been shown that the 

 infested squares remain on the plants for approximately 11 days 

 after egg puncture. For fully 8 days after egg puncture the sap 

 continues to flow to the injured squares and keeps the temperature 

 lower than is required for proper weevil development. At night the 



