136 THE MEXICAN COTTON-BOLL WEEVIL. 



The weevil has frequently been observed to experience considerable 

 difficulty in reaching the cotton square through the involucral bracts. 

 If these bracts are united at the Dase, or very closely appressed, or 

 have their edges provided with strong hairs, the natural difficulty the 

 weevil experiences will be increased. 



Dr. Cook has pointed out that certain Central American strains of 

 cotton have bolls provided with thick interior walls, which in some 

 cases the weevil is unable to penetrate. 



As has been pointed out in another section, the insect enemies of the 

 boll weevil find the infested squares which remain on the plants more 

 suitable for attack, and are able to raise the average control above 

 that in fallen squares in most sections. Consequently it is of advan- 

 tage to the planter to have a variety with a well-marked tendency to 

 retain the infested fruit. The ability to retain the infested squares 

 is explained under the heading of parasite attack (p. 144). 



Several other peculiarities of the cotton plant which Dr. Cook has 

 interpreted as weevil-resisting adaptations are described in Bulletin 

 88 of the Bureau of Plant Industry of this department. 



DISEASES. 



Little attention has been given to the study of diseases of the boll 

 weevil because the observations upon the mortality of the insect have 

 not indicated any great amount of death due to causes which could 

 not be well explained under the headings of climatic, plant, parasitic, 

 and predatory control. There is no doubt that bacterial and fungous 

 diseases sometimes attack the weevils, especially those hibernating 

 in moist places. Only two definite records are at hand of death by 

 fungus, and these have been recorded in former bulletins. One was 

 a case of a new species of Aspergillus and the other of a species of 

 Cordyceps. 



PARASITIC AND PREDATORY INSECT ENEMIES. 



Recent work has added very greatly to our knowledge of the insect 

 enemies of the boll weevil. Much remains to be done, however, 

 since it has been found that the boll weevil is accumulating species 

 after species of parasites as it advances farther into the United States. 

 A recent publication of this bureau (Bulletin No. 100) has dealt 

 rather extensively with the insect enemies of the boll weevil. In the 

 present publication, therefore, only a few of the more important facts 

 learned will be considered. 



A BRIEF SUMMARY OF THE INSECT SPECIES ATTACKING THE BOLL 



WEEVIL. 



At the present time the boll weevil is known to be the host of 29 

 species of parasites, of which 4 are mites, 21 belong to the order 

 Hymenoptera, and 5 are parasitic flies. In addition to these true 

 parasites, there are 6 predators which kill the adult boll weevils and 

 22 predators which attack the immature stages. These include a 

 mantis, a predatory bug, 8 beetles, a leaf-feeding caterpillar, and 17 

 species of ants. In all, the boll weevil is known to have 58 species 



