BIOLOGY OF ARIZONA WILD COTTON WEEVIL. 9 



in the sun produced none. Those immersed 30 minutes and placed 

 in a dry tumbler in the shade produced one weevil. 



These results indicate the importance of moisture in the emergence 

 of the weevils. Mere placing on moist sand caused some weevils 

 to emerge in 5 days, but the bolls moistened and then placed on 

 moist sand in the shade produced the maximum emergence. ' In 

 the various lots which were placed in the sun not a single weevil 

 emerged regardless of treatment. This was evidently due to the 

 extreme heat in the tumbler. All weevils were found dead in these 

 cells upon examination while many of those in the shade were still 

 alive in the cells. 



These experimental tests of the factors producing emergence are 

 far from conclusive, but by combining them with various observa- 

 tions made in the field a fairly definite idea of conditions under which 

 the weevils will emerge may be secured, and by studying the sea- 

 sonal climatology of the region inhabited by the weevils it is possible 

 to know when to expect the emergence. 



The emergence of the weevil shows a very decided relation to the 

 structure of the Thurberia boll and is the result of a gradual prepa- 

 ration of the boll which extends over a considerable period of time. 

 In the fall the weevil cell is surrounded by the compact seeds and these 

 in turn are inclosed in the covering of the boll. These soon dry and 

 harden so that emergence is impossible. Then follows a slow chang- 

 ing of the boll extending through the winter months. The seeds 

 around the cell ripen, harden, and separate slightly. The outer 

 covering of the boll cracks apart at the apex and gradually splits 

 toward the base. While this is largely a process of ripening and 

 dessication, it is undoubtedly aided by the occasional rains during 

 the winter and early spring. By spring the boll reaches a condition 

 such that it is easily opened and the seeds scattered by a light crushing, 

 but now the weevil cell itself holds the contents intact. In fact 

 most of the uninfested bolls have opened wide by this time and the 

 seeds have been blown and shaken out by the w^nd. 



At this period it seems usually necessary for the boll to be at least 

 slightly moistened to soften the cell before the weevil can emerge. 

 The tests of the amount of moisture required to accomplish this 

 show that it is variable and that very little is necessary in some cases. 



That moistening is not always necessary to allow emergence is 

 shown by the fact that the writer has observed weevils both in the 

 field and in the laboratory emerging from perfectly dry bolls which 

 had not been moistened for weeks. These cases seem to be due 

 to the imperfect formation of the cell, which is weak enough to 

 be broken by the drying of the boll and separation of the seeds. 



From these observations concerning the importance of moisture 

 in the emergence of the weevils, it seems quite probable that in the 

 14889°— Bull. 344—16 2 



