HIBERNATION. 95 



The long absence of the weevils from the cotton fields has led super- 

 ficial observers to believe that the weevils pass the egg stage in the 

 cotton seed. Such persons point out the fact that the weevils are 

 found in seed houses and appear most abundantly in the fields near 

 these buildings, and also that they have found insect larvse in the 

 seed. As a matter of fact, the insects found in the cotton seed are not 

 boll weevils, but other species which feed upon dried seeds and 

 similar vegetable matter. The appearance of the early weevils in the 

 vicinity of seed houses is due entirely to the fact that the protection 

 offered there attracts many in the fall. Careful observations through- 

 out the winter have shown that the boll weevil remains inactive except 

 for very slight movements during very warm periods and that it does 

 not breed in or feed upon cotton seed. 



As explained in another portion of the bulletin, the hibernation 

 period is defined by the continuance of mean temperatures within 

 what we define as the zone of hibernation. This zone has as its upper 

 limit the mean temperature above which, if continued for any con- 

 siderable period, the life activities must be resumed, and has for its 

 lower limit the absolute temperature below which no weevil can live 

 for even a short time. For all practical purposes the hibernation zone 

 lies between 56° and 12° F. 



METHODS OF STUDY OF HIBERNATION. 



In studying several features of the hibernation of the boll weevil 

 the practice has been to utilize large cages covered with wire screen 

 which were placed in the cotton fields. (See PI. X, b.) No cotton 

 was grown in these cages, but at different dates in the fall large num- 

 bers of weevils collected in the adjoining cotton were placed in the 

 cages. It has been considered that the rate of survival of weevils in 

 these cages installed chronologically is an index to the number of 

 weevils that actually survive under natural conditions. It has thus 

 been considered that with 1,000 weevils in a cage installed October 1, 

 which showed a survival of 10 per cent, and a cage containing 1,000 

 weevils installed on September 15, which showed a survival of 5 

 per cent, twice as many weevils would have survived the destruction 

 of the plants on October 1 as on September 15. Although there is no 

 doubt that this method gives a fairly accurate index, there is one 

 objection that can be made to it. This objection is that the number 

 of weevils leaving the field to go into hibernation as the season 

 progresses, the number dying in the fields, and the number maturing 

 there are not taken into consideration as the calculations have been 

 made. On September 15 none of the weevils in the field would have 

 entered into hibernation. By the 1st of October, however, a certain 

 number would have left the field, and such weevils would not be 

 represented in the collections made for the cage installed on October 1 . 

 It is not known whether the weevils which remain in the fields late 

 are more or less hardy than those which leave early to find hibernating 

 quarters. The indications, however, are that the stronger and more 

 active wee vils — that is, those more likely to survive the winter — are the 

 ones which do not go into hibernation at an early date. Nevertheless 

 the number that may have gone into hibernation between the dates 

 of the installation of the various cages, the number that died from 

 natural causes, and the number that matured in the fields during that 



