16 FARMERS BULLETIN 848. 



times crushes the immature weevOs, and determinate growth, 

 which may prevent the development of the fall broods of the 

 weevil. Attention is also called to the agency of birds in the 

 destruction of the boll weevil, which has been given full attention in 

 the pubUcations of the Biological Survey of this department. 



DISSEMINATION. 



The boll weevil moves from place to place by fhght. Although it 

 is a weak flyer compared with many insects, it has been kno%\'ii to 

 cover a distance of more than 40 miles in a very short time. Its 

 flight can not be prolonged, but successive short flights, especially 

 in connection with favorable winds, often carry the insect to consid- 

 erable distances. This is the case, however, only during the so-called 

 dispersion period, which extends from about the middle of August 

 to the end of the season. During the rest of the year the weevil is 

 little inclined to fly. There is always a movement from fields in all 

 directions in search of hibernating quarters in the fall and a corre- 

 sponding movement from such quarters to the cotton fields in the 

 spring. Nevertheless, when the insects reach cotton fields in the 

 spring there is Httle further movement until the general dispersion 

 begins. Ordinarily between the middle of August and the first of 

 September the weevil seems to be seized with the instinct to migrate. 

 It was thought at one time that this movement was forced by exces- 

 sive reproduction and took place only when all squares and bolls, or 

 the majority of them, became infested. Investigations have sIio-vnti, 

 however, that the dispersion takes place frequently when the fields 

 are only sUghtly infested. In other words, the insect has a weU- 

 developed instinct for extending its range into new territory. It is 

 this instinct that has caused the extension of the infested area in the 

 United States year by year. The weevil does not fly in any particular 

 direction except as governed by the wind. If there is no wind, or 

 only a light one, a weevil is as hkely to fly in one direction as in 

 another. Tlie individuals carrying the infestation into new regions 

 are those that happen to radiate in the direction of previously unin- 

 fested territory. 



The fact that the weevil moves about very httle except at one 

 season is of great benefit to the planter. As the movement referred 

 to does not begin until after the time when a crop normally is made, 

 it amounts to little after a region has become infested. On the 

 other hand, the Umited movement at other times of the year makes 

 it possible for any individual farmer to obtain the best results from 

 his own efforts in fighting the pest. The danger that his efforts will be 

 thwarted by the arrival of weevils from fields where no precautions 

 have been taken is not so important as it is sometimes considered. 

 In fact, it is not important enough to warrant any farmer in deferring 

 action on account of the indifference of liis neighbors. 



