12 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



be checked by this temperature factor, and it was hoped that this 

 would occur before the northern limit of profitable cotton production 

 should be reached. Unfortunately, the insect has shown that it is 

 capable of a considerable amount of adaptation to this change in 

 temperature conditions, so that its northward range has been gradu- 

 ally extended until, in the season of 1906, it crossed the Red River 

 Valley and became established in the southern portion of Indian 

 Territory. Humidity has proved to be an important factor, affecting 

 more the abundance and injuriousness of the species than it does 

 its distribution. 



Considering some of the broader aspects of the effect of tempera- 

 ture and humidity in controlling the weevil, it appears that the most 

 marked instances of definite control have been occasioned by what 

 may be termed the unusual variations, either above or below the 

 usual range, in these factors. Thus it seems to be prolonged peri- 

 ods of extreme heat in summer and the exceptional depression in 

 temperature in winter which have produced the most clearly marked 

 results. When these exceptional conditions occur, they affect, as 

 a rule, rather extensive areas, so that the good results are general 

 instead of localized, as is likely to be the case with many of the factors 

 which will be considered in succeeding pages. The possible effect 

 of high summer temperatures has been the prime reason for recom- 

 mendations designed to secure a proper spacing of the plants, which 

 would leave weevil-infested squares most directly exposed to the 

 sunshine. It frequently happens that this factor is sufficiently 

 effective to so check severe weevil attack as to allow the cotton to 

 set and to mature a reasonably good crop. It is especially effective 

 if occurring early in the season during the period when the plant is 

 normally setting its crop of fruit. Its value may be completely 

 neutralized by other coincident or preceding conditions, such as a 

 very rank growth of the plants, or a too close planting, which may 

 cause the plants to shade a large proportion of the fallen forms. 3 



INFLUENCE OF SHORT DROUGHT IN SAME SEASON. 



A definite illustration of the control of the weevil, largely by pro- 

 longed and excessive heat, was found at Victoria, Tex., in 1906. 

 The plat of cotton under observation covered only one-half acre, so 

 that it was possible to make frequent and close observations upon 

 the conditions prevailing on the entire plat. Table I presents a 

 brief summary of temperature, rainfall, crop, and weevil conditions 

 for this area during a period of four months from the planting of 

 the seed. 



a The term "forms" is used for convenience to include all stages of the cotton fruit: 

 The bud or square, the bloom or flower, and the boll or seed pod. 



