OP WASHINGTON, VOLUME XIII, 1911. HI 



The fourth paper on the program was by Mr. Pierce, en- 

 titled: 



4 



SOME FACTORS INFLUENCING THE DEVELOPMENT OF THE 



BOLL WEEVIL. 



BY W. DWIGHT PIERCE. 



For several years I have been endeavoring to find the law 

 of effective temperature which governs the development of 

 the boll weevil. Soon after beginning studies of the develop- 

 ment of the insect, it was found that the use of 43 degrees as 

 the zero of effective temperature was erroneous, but it has 

 been a very difficult matter to find the correct substitute for 

 this point. It has been more or less the fashion in entomo- 

 logical life-history studies to consider 43 degrees as the zero of 

 effective temperature for all insects. The first authors that I 

 can find who threw some doubt upon the validity of this law 

 were Messrs, Ouaintance and Brues, in their bulletin on the 

 cotton bollworm. In this bulletin they stated that it appeared 

 to them that between 58 and 60 degrees Fahrenheit was more 

 nearly correct for the bollworm than 43 degrees. Later, Pro- 

 fessor Sanderson, in a series of papers, pointed out the gen- 

 eral fallacy of assuming that 43 degrees is the zero for all 

 insects. He stated that it was his opinion that each insect 

 was governed by its own climatic laws and that it would 

 probably be found that a different zero of effective tempera- 

 ture held for each species of insect. 



The usual method of obtaining the zero of effective temper- 

 ature is by using the daily mean temperatures during the 

 period of observations and the total length of the develop- 

 mental period with a sufficient number of observations given 

 under quite a range of temperatures. It is possible by means 

 of frequent testings to ascertain the point above which an ac- 

 cumulation of daily units of temperature will give the least 

 variation. This point is considered the zero and the total 

 effective temperature is the product of the average daily mean 

 temperature above the zero multiplied by the average number 

 of days. In this manner it has been found that 56 degrees 

 more nearly approximates the zero of effective temperature 

 for the boll weevil than 43 degrees. The studies showed, 

 however, that there was considerable variation in total effec- 

 tive temperature which must be due to some other cause, and 

 it was also apparent that it would be necessary to ascertain a 

 different zero of effective temperature for each locality unless 

 it was possible that some other factor held a controlling in- 

 fluence in the development. In this manner the question 



