22 BULLETIN" 344, IT. S. DEPARTMENT OF AGRICULTURE. 



The fact that while 154 bolls showed signs of weevil injury, only 

 30 (19.4 per cent) contained live adults on January 2, indicates a 

 very high larval mortality. Most of the injured bolls containing no 

 stages showed only one or two seeds eaten out by larvae, though in 

 some the injury was more extensive. Whether or not this high 

 larval mortality is found in nature is open to doubt, but the cage 

 conditions veiy closely approximated those under which the lower 

 plants and weevils exist. This larval mortality may explain one 

 puzzling point in connection with the interrelation of the Thurberia 

 plant and weevil — that is, why the weevil does not multiply entirely 

 out of proportion to the abundance of its very restricted host plant 

 when the females are evidently so extremely prolific in egg deposition. 



ON COTTON PLANTS. 



In the same manner that these weevils were tested upon growing 

 Thurberia plants, others were tested on growing cotton plants. 

 Five cages, three large and two small, were placed over rows of 

 plants about 16 inches tall. These plants were all bearing squares, 

 blooms, and bolls. A general view of these cages is shown in Plate II, 

 figure 2. All weevils were collected feeding on Thurberia in the Santa 

 Rita Mountains September 25 and kept without food for four days. 



The weevils were introduced into the various cages September 29. 

 The small cages (Nos. 8 and 9) each received two males and two 

 females while the large cages (Nos. 3,6, and 7) each received four of 

 each sex. Following the introduction of these weevils the cages were 

 examined frequently until October 31. The following is a summary 

 of the injured forms which fell from the plants during this period: 



Cage No. 8, 11 small bolls. 



Cage No. 9, 14 small bolls, 2 squares. 



Cage No. 3, 22 small bolls, 2 squares, and 1 bloom. 



Cage No. 6, 13 small bolls, 3 squares, and 1 bloom. 



Cage No. 7, 18 small bolls, 1 square. 



It is interesting to note that all the egg deposition was in the bolls. 

 In fact there was only a comparatively small amount of feeding on 

 the squares and little more on the blooms. For egg deposition the 

 female seems to prefer bolls from about one-fourth to one-third 

 grown. Some of the smallest of these drop from the plant when the 

 larval injury becomes severe but nearly all remain hanging. 



On October 31 a final examination of all cages was made. At this 

 time the leaves and other trash piled in the cage was examined for 

 hibernating adults and the plants were examined for active ones. 

 One weevil was found active on the wall of a cage, one was feeding 

 on a bloom, and one was dead inside the bracts of a boll. One male 

 and one female, both dead, were found at the bottom of a pile of 

 trash. 



