97 



percentage of larvae and pupae killed was much larger than in the 

 native. In native cotton about 20 per cent of the larvae were found 

 to be dead, while in the King 41.2 per cent were dead. In all proba- 

 bility the more rapid flow of sap in the early developing King cotton 

 was largely responsible for the changes which led to the death of the 

 larvae. 



CLIMATIC CONTROL. 



INFLUENCE OF CLIMATIC CONDITIONS UPON WEEVIL MULTIPLICATION 



AND INJURY. 



Three principal factors affect the development, spread, and destruc- 

 tiveness of the boll weevil — temperature, precipitation, and food sup- 

 ply. So perfectly has the weevil become adapted to its single food 

 plant that it is a very noticeable fact that the climatic conditions which 

 are most favorable to the growth of the plant are most favorable also 

 for the normal activities and development of the weevil. Affecting 

 one in the same direction as the other, the pest is, therefore, enabled to 

 very closely keep pace with its food supply under all kinds of natural 

 conditions. 



The most favorable conditions for the weevil are a high tempera- 

 ture and abundant moisture throughout a long season. These con- 

 ditions favor the growth of the plant and produce a very large 

 number of squares, which supply abundant opportunity for the rapid 

 multiplication of the weevils. Severe drought checks together the 

 growth of the plant and the development of the weevils. It has not 

 yet been determined whether the death of larvae in fallen squares 

 exposed directly to the rays of the sun is due principally to the heat 

 jDroduced or to the complete drying of the food supply. It is certain, 

 however, that one or both of these factors produce a large mortality 

 among the larvae and pupae so exposed during long-continued hot and 

 dry weather occurring before the plants have become large enough 

 to shade most of the ground. After that the shade produced pre- 

 vents most of the good work of the sun in destroying weevils. 



It is often said by cotton growers that "rain brings the weevils." 

 The principal reasons for this idea are that rains, in squaring time 

 especially, produce conditions greatly favoring the immediate devel- 

 opment and subsequent injury of weevils, while at the same time 

 they make more apparent the amount of injury already done. An 

 abundance of rain following a long dry period naturally causes great 

 numbers of squares to fall from purely physiological causes, while at 

 the same time it knocks to the ground such previously infested 

 squares as have become weakened in their connection with the plant 

 and which would fall naturally within a few days. The large number 

 of squares to be found on the ground immediately after a storm would 

 seem to account for the prevalence of the opinion mentioned. A 

 large degree of moisture in fallen squares seems to favor directly the 

 21739— No. 45—04 7 



