119 



EFFECT OF MAXIMUM INFESTATION UPON WEEVIL MULTIPLICATION. 



As may be seen b}^ reference to Tables XXIX, XXX, XXXI, 

 XXXII, and XXXIII, maximum infestation is usually reached some 

 time between August 1 and 20. It is probable that at that time the 

 majority of the third-generation weevils are becoming adult. As 

 shown on page 97, a conservative estimate would place the possible 

 number of third-generation weevils at about 250,000 individuals. 

 This number is practically all that can be produced upon each acre of 

 ground. As soon as they become adult, therefore, and begin to 

 attack squares, the field, within a few days, becomes overstocked with 

 weevils. 



A decrease in square production accompanies the maturity of the 

 bulk of the crop, owing to the fact that the assimilative power of the 

 plant is largely consumed in maturing seed. Dry weather normally 

 occurring at this period also causes a decrease in the number of weevils 

 present. Not only are there less squares to become infested, but each 

 square is also subjected to greater injury, and many which would other- 

 wise have produced weevils are unfitted as food for the larvae by the 

 decay which follows the numerous punctures. Several eggs may be 

 deposited in one square, but as a rule only one weevil will result. 



By this time the number of weevils has become so great that the 

 supply of squares is insufficient to meet their need for both feeding 

 and oviposition. Selection of squares, so that these two portions of 

 their attack m&y be kept separate, can no longer be exercised. Female 

 weevils are forced to deposit their eggs in squares which have either 

 received other eggs or been largely fed upon, and a much larger pro- 

 portion of squares at this time show that feeding punctures are made 

 in squares having eggs or larvae. By these two factors the mortality 

 among young larvae especially is greatly increased. Since the growth 

 of the plant practically ceases during the period when the majority of 

 bolls are opening, new squares are not formed, and consequently the 

 number of weevils produced through September becomes compara- 

 tively small at that time; also many of the older weevils, especially 

 those of the first generation, die normally. Comparatively few of the 

 weevils developed in large bolls will emerge before October. In con- 

 sequence of all these factors the actual multiplication of the weevil is 

 not only checked but very greatly reduced within a few weeks after a 

 condition of maximum infestation has been attained. While the actual 

 number of weevils begins to decrease within a short time after the 

 period of maximum infestation is reached, the apparent numbers may 

 possibly be greater. The decreased number of squares serves to con- 

 centrate the weevils upon those remaining, and therefore the number 

 of weevils found in airy square will be so much the greater. 



