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



THE RELATION OF TEMPERATURE TO THE BIOLOGY OF THE 



BOLL WEEVIL. 



The relationship of temperature to the biology of the weevil has 

 been thoroughly studied for the adult weevil. Little information is 

 available, however, showing the effect of temperature on the imma- 

 ture stages of the weevil. For years the Bureau of Entomology has 

 made so-called status examinations in different parts of the weevil- 

 infested area of the cotton belt to determine the percentage of mor- 

 tality caused by the heat and dry weather in the immature stages 

 of the weevil. From an examination of 91,082 immature weevil 

 stages Hunter and Pierce 10 found 23.8 per cent killed by heat and 

 dr} r ness. This examination extended over the different months of the 

 growing season from May to October. The relatively small per- 

 centage of mortality among the immature weevil stages recorded in 

 this examination is misleading, because the life of the immature 

 weevils was not followed through until the weevil became adult. 

 From the writer's observations at Madison, Fla., the critical period 

 of the immature weevil caused by intense heat seems to extend to 

 the teneral adult stage. Hundreds of teneral adult weevils were 

 observed in squares in the field hatchery that were killed by the 

 heat before they could make an emergence hole in the square. There- 

 fore an examination made to determine the percentage of mortality 

 caused by heat and dryness on any given date is misleading for the 

 simple reason that, although the percentage of immature stages 

 dead may not run very high at the time of examination, yet if it 

 were possible to follow these stages through to emergence of the adult 

 weevil the figures might be trebled. As a concrete illustration, 

 on June 25, 1919, Dr. Pierce examined 451 weevil stages in fallen 

 brown squares taken from plants on which tagged squares were 

 hanging or had fallen. Of the 451 stages examined 134, or a per- 

 centage of 38.95, had been killed from climatic causes. At the time 

 this examination was made the writer had 1,378 fallen punctured 

 squares that were tagged on the day of egg-puncture under observa- 

 tion for breeding records. Dr. Pierce's examination indicated that 

 38.95 per cent of the 1,378 fallen punctured squares would not hatch 

 weevils, since the punctured squares used in his examination were 

 taken from underneath the plants where tagged squares belonging 

 to the writer were lying. However, of the 1,378 squares that were 

 tagged, only 134, or 9.7 per cent, produced adult weevils. It is evident 

 that a field examination is misleading in so far as the percentage of 

 control of the immature weevil stages by heat and dryness is con- 

 cerned unless these stages can be followed through to the emergence 

 of the adult weevil. 



"Hunter, W. D., and Pierce, \V. D., op. cit 



