THE MONTHLY BULLETIN. 



293 



The weevils also deposit their eggs in cotton bolls, even full-grown bolls, but owing 

 to the cooler interior of the boll and the less nutritive substance, development takes 

 place very much more slowly. The hard carpel linings often prevent placing the 

 egg on the surface of the fiber and frequently the larva hatches and never gets into 

 the liber and seeds. The seed furnishes the principal food for the larva. Often a 

 boll will contain several larva', but a single one can ruin one or two locks. 



The adults have a habit of dropping when disturbed, and feigning death. They 

 are most active during the daytime. They are strong fliers, capable apparently of 

 long-sustained flight, but usually fly only from plant to plant, or field to field. 



In the fall of each year the number of weevils becomes so great that the fields are 

 overstocked. The lack of food causes multitudes to rise in flight and to disperse in 

 all directions. In this way the annual fall dispersion takes place, which has carried 

 the species from 20 to 200 miles a year toward the east, and less rapidly north- 

 ward. Storms have also been instrumental in spreading them into new territory. 



The distanc f the annual movement depends on the number of weevils seeking 



food and the amount of food available; hence areas of great abundance of cotton 

 serve to retard spread, and areas of cotton sparsity force extensive spread. 



The fall dispersion is checked by killing frosts and the weevils seek the best shelter 

 to be found. Along the Gulf coast the presence of Spanish moss furnishes ideal 



Fig. 92. A Mexican cotton boll weevil (Anthonomus grandis Boh.) and the 

 cotton square from which it emerged. (Photo by L. A. Whitney.) 



shelter for multitudes of weevils. Many find satisfactory quarters in the woods. 

 old Stumps, fence rows and even underground on cloddy fields. Corn stalks and 

 weeds also provide shelter for many. 



Usually less than 10 per cent of these entering hibernation survive to attack the 

 next year's crop, but with from four to eight generations and an average offspring 

 of 300, of which half are males, the survival of a single fertilized female is sufficient 

 to stock a field. 



Fortunately the natural control averages over 50 per cent and often runs above 

 98 per cent in a given locality, hut the annual dispersion usually fills up the weak 

 spots. Extreme cold weather in which a minimum of 10 degrees is reached before 

 the weevils enter hibernation is very fatal. Likewise very hot dry weather is fatal. 

 A combination of these factors caused the weevil to lose for several years the 

 northern part of the black prairie of Texas, but changing climate in subsequent 

 years enabled the species to regain all lost territory. Actual exposure to 10 d 

 or 123 degrees for a short time is fatal. The normal soil temperature on a hot 

 summer day is higher than 123 degrees, therefore, if the infested squares fall on 

 heated ground exposed to the sun for several hours the larvae will die. For this 

 reason the rows should be planted in such a direction as to give the longest period 

 of sun-heat to the middles. 



