ENTRANCE INTO HIBEENATION. 17 



From this record it appears that at the time of entering hiberna- 

 tion male weevils largely predominate, being in the proportion 

 approximately of 3 males to 2 females. 



NUMBER OF ADULT WEEVILS ENTERING HIBERNATION. 



It is evident that determinations bearing upon the number of 

 adult weevils entering hibernation must in all cases be largely in 

 the form of estimates because of the physical impossibility of making 

 a thorough examination of more than a comparatively small fraction 

 of an acre. In our own determinations upon this point we have fol- 

 lowed the general plan of selecting average crops of plants in four 

 or five different portions of the field, representing, so far as ma^^ be 

 possible, different conditions in the growth of the plants which may 

 influence the number of weevils to be found. The number of plants 

 per acre is ultimately the basis upon which the estimate as to the 

 number of weevils per acre is based. It is evident that the number 

 of plants will vary widely in different localities. For example, in 

 the river valleys, where the growth of the plants is rank, the average 

 number may be about 5,000; whereas upon poorer land, where plants 

 never become large, the number per acre may be as great as 10,000.' 

 From estimates made upon several hundred fields during the past 

 two years it appears that the average number of plants per acre is 

 not far from 7,000. We beheve that this method of estimating 

 the number of weevils per acre is more desirable and reliable than an 

 estimation of the number of weevils per plant in which the fractions 

 found in an average must be disregarded. 



In the fall of 1903 Prof. E. D. Sanderson found from his own obser- 

 vations and from reports of correspondents an average of from one 

 to two weevils per plant. In the fall of 1904 an examination of 

 four fields at Terrell, Tex., showed a variation of between 762 and 

 over 29,000 weevils per acre. This wide variation was due primarily 

 to the effect of defoliation by the cotton leaf-caterpillar in one field, 

 that having the exceptionally large number of weevils not having been 

 defoliated. These points are mentioned particularly to show the 

 wide variation which may occur within very short distances and also 

 to emphasize the effect of the work of the leaf-worm in accomplish- 

 ing what is practically a more or less complete destruction of the 

 stalks. 



90317— Bull. 77—09 2 



