144 



THE MEXICAN COTTON-BOLL WEEVIL. 



anil semicluster types, are distinguished by an elliptical mark which 

 encircles the pedicel, but extends down the stem for one-half to a 

 whole inch or more, and is usually incomplete at the lower end. 

 When such a square is injured, the corky layer is of course diagonal, 

 extending downward on the stem, but usually incomplete, so that 

 the injured member adheres by a thread of bark ancl dries on the 

 plant. A very extended series of observations has definitely proved 

 that the hanging dry infested square is the most favorable place for 

 parasitic control and that the total control of the weevil by all causes 

 increases in proportion to the number of these hanging dry infested 

 squares. A proper selection of varieties is, therefore, a practical 

 method of increasing control. 



On the other hand, it must be understood that insect control of the 

 stages in fallen squares is often very high. Certain parasites and all 

 of the ants and predatory beetles are more likely to find the immature 

 weevils in the soft moistened or dried fallen squares than in the diy 

 hanging squares. Thus the developing weevil has enemies wherever 

 it is. The parasite control on the ground will be obtained best by 

 the methods of cultivation to be mentioned hereafter. 



The adjustment of new species of parasites and predators in each 

 new region makes it apparent that the boll weevil will everywhere 

 be attacked by those species of insects most fitted to attack it under 

 the existing local conditions. This attack will be of greatest impor- 

 tance in regions where humidity tends to reduce the effectiveness of 

 other forms of control. 



By Table LXIII we show the final summary of the records of para- 

 sitism made for a period of years to illustrate the fact that this is a 

 factor of great importance. 



Table LXIII. — Parasite control of the boll weevil, by years. 



Table LXIII is based upon collections of squares and bolls made 

 throughout the infested territory under a great diversity of conditions. 



The average monthly parasitic and predatory control for the years 

 1906 to 1909, inclusive, has been arranged below (Table LXIV) to 

 show that insects are a factor of importance throughout the year. It 

 should be noted especially that in the months of August and Septem- 

 ber, when the boll weevils are most numerous, from 27 to 30 per cent 

 of the immature stages are killed by insect enemies. The average 

 for the year of 25 per cent offers great encouragement. 



