268 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



and varieties which produce little shade is therefore apparent, and 

 it is evident that injury will be much less on dry upland soil, and 

 much more severe in bottoms where the cotton grows rank and 

 thick. 



Over a score of parasites* prey upon the immature stages 

 within the squares or bolls, and they seem to be increasing in num- 

 bers and effectiveness as they become adapted to living upon the 

 weevil, as they are all native insects which prey upon nearly 



FIG. 198. Chain cultivator for use in drawing weevil infested squares to center 

 of row. (After Hunter, U. S. Dept. Agr.) 



related species of weevils and other insects. Ac many as two-thirds 

 of the immature stages have been destroyed by them in certain 

 fields, though ordinarily not over 5 per cent of the total are para- 

 sitized. Several species of ants also feed on the immature stages, 

 20 to 30 per cent of those in fallen squares and bolls often being 

 destroyed by them. The ants destroy many more in the fallen 

 squares than in those hanging on the plants, so that the dropping 

 of the squares aids their good w r ork as w^ell as exposes the squares 

 to the heat of the sun. 



Usually about 70 per cent of the infested squares drop, and in 

 these 70 to 80 per cent of the immature stages are destroyed by 

 natural causes.f 



* See W. D. Pierce, Studies of Parasites on the Cotton Boll Weevil, 

 Bulletin 73, Bureau of Entomology, U. S. Dept. Agr. 



t See W. E. Hinds, Some Factors in the Natural Control of the Mexican 

 Cotton Boll Weevil, Bulletin 74, Bureau of Entomology, U. S. Dept. Agr. 



