95 



the average total effective temperature required for development in 

 bolls was therefore 1,933.7° F., or nearly two and one-half times as 

 much as in squares. Several larvae often develop within a single boll 

 (PI. XVI, hg. 71). They appear to remain in the larval stage until the 

 boll becomes sufficiently mature or so severely injured as to begin to 

 dry and crack open. When this condition of the boll is reached, 

 pupation takes place, and by the time the spreading of the carpels is 

 sufficient to permit the escape of the weevils they have become adult. 



BROODS OR GENERATIONS. 



The term ''brood" can hardl}' be applied in its usual sense to the 

 generations of the weevil, as was pointed out by Doctor Howard in the 

 first circulars of the Bureau dealing with the problem. For several 

 reasons no line of distinction can be drawn between the generations in 

 the field at any season of the year, not even between hibernated wee- 

 vils and the adults of the first generation. As has been shown, the 

 period of oviposition among hibernated females is in some cases fully 

 3 months, while it averages 48 days. The average period of the full 

 life cycle for the first generation, as shown in Table XXII, is 25 days, 

 and as the time for the second generation would be slightly less, it is 

 evident that the first eggs for the third generation may be deposited at 

 the same time as those for the middle of the second generation, and 

 also with the very last of the eggs deposited by hibernated females 

 for the first generation. The great overlapping of generations thus 

 produced prohibits the application of any of the common methods of 

 ascertaining their limits. The complexity indicated for the first three 

 generations becomes still further increased as the season advances, so 

 that in October, for example, a weevil taken in the field might possibly 

 belong to any one of five or six generations. Duration of life and the 

 period of reproductive activity are important factors in determining 

 the average number of generations. Periods of greatest abundance 

 can not be regarded as giving any reliable information upon this point, 

 since the number of weevils developed soon comes to depend largely 

 upon the supply of squares. 



In the case of the boll weevil, therefore, the information upon the 

 number of generations must be drawn mainly from laboratory sources, 

 but the results are supported by observations made in the field. Many 

 of the hibernated weevils continue to deposit eggs until the middle of 

 July, and some are active for fully a month longer. In 1903 the last 

 eggs from hibernated weevils were deposited on August 27. In the 

 course of breeding experiments made in 1902 it was found that many 

 weevils which had become adult about the 1st of August would con- 

 tinue to deposit eggs until the latter part of November. Considering 

 the longest-lived weevils and their last-laid eggs, therefore, it is easily 



