NATURAL CONTROL. 121 



The most conspicuous illustration of the climatic control of the 

 weevil lies in the failure of the pest to establish itself in the drier 

 portions of Texas. For several years multitudes of weevils have 

 flown from the more humid portions of Texas to the west, where the 

 climate is drier. In fact, every year there has been a large inflow of 

 weevils into this region. Every season, however, the conditions have 

 practically immediately prevented the establishment of the weevil. 

 The most important factor has been dryness, but there are others that 

 must be considered. Among them is the fact that there is com- 

 paratively little winter protection for the insect. In addition, an 

 indirect result of small precipitations is the growth of cotton plants of 

 only small size. This results in a small amount of shade and thus 

 augments the direct effect of heat and dryness upon the infested 

 squares which fall to the ground. 



Frequently the effects of climate act upon the enemies of the boll 

 weevil. This is the case where heat destroys the weevils and their 

 parasites in squares that fall to the ground. In several cases, how- 

 ever, heat increases the effectiveness of the enemies of the weevil. 

 A striking example of tins was observed on September 2, 1911, by 

 Mr. J. D. Mitchell, of the Bureau of Entomology. A succession of 

 days in which the temperature was very high and the air exceedingly 

 dry caused the premature opening of many cotton bolls in the vicinity 

 of Victoria, Tex. Prior to this time the weevils had destroyed prac- 

 tically all of the squares, and many immature stages were to be found 

 in the bolls thus forced open. In such instances the exposed imma- 

 ture stages of the weevil were subjected to two important destructive 

 agencies. Heat killed many that became exposed to the air, and the 

 ants were able to reach not only those that were exposed, but others 

 inside of the partially opened bolls. If the bolls had not opened, 

 such weevils would have been beyond the reach of the ants. As it 

 was, the climatic conditions not only directly destroyed large num- 

 bers of weevils in a situation where climatic factors rarely affect them, 

 but also greatly increased the effectiveness of another unrelated factor 

 of control. 



CLIMATIC INFLUENCES ON VITALITY AND ACTIVITIES. 



In the preceding pages numerous effects of climate upon the devel- 

 opment and activities of the boll weevil have been pointed out, but 

 these must be summarized in order to show how intimately connected 

 the climate is with every phase of the weevil's life. It appears that 

 the movements of the weevil are sluggish or active in accordance with 

 the nature of the day, cloudy days or low temperatures always causing 

 them to be more sluggish. The number of feeding punctures per 

 square decreases with increases in temperature, and the time before 

 falling of a punctured square also decreases with higher temperatures. 

 In like manner the length of life of the weevil decreases. The age of 

 beginning copulation and the age of beginning oviposition are both 

 increased by decreases in temperature. The activity in oviposition, 

 which is found to begin at 75° F., is greatest in the hottest time of the 

 day, cloudy days causing the oviposition to be less active. The num- 

 ber of eggs per day increases with the temperature and varies for any 

 given temperature with the .humidity. The entire period of develop- 

 ment increases as the temperature and atmospheric humidity decrease. 



