CLIMATIC CONSIDERATIONS. 33 



great wave of boll- weevil emergence. A glance at the accompanying 

 diagrams (figs. 4, 5) will show that in Louisiana tlie monthly mean 

 temperature was from 3° Fahrcnlieit (November) to 10° (January) 

 higher than the normal, and in Texas it varied from normal 

 (November) to 10° above normal (Marcli) during the entire winter. 

 On the other hand, the accumulated moisture fi'om November 1, 

 1906, to March 1, 1907, in Louisiana was 5 inches below normal and 

 in Texas 1 inch below normal. 



Cotton was planted in March and April (1907) and normally would 

 have squared in May and June, but it was retarded a month by the 

 low temperature in Ai)ril and May, during which months the monthly 

 mean temperature was 2° to 3° below normal in Louisiana and 

 3° to 6° below normal in Texas. In addition to the cold of the 

 spring, the precipitation in Louisiana from March 1 to July 1 

 was 7 inches above the normal and in Texas 2 inches above. This 

 cold and the presence of volunteer cotton tided the boll weevil over 

 until the planted cotton was up. The parasites were obliged to seek 

 cohosts from March 15 until late in May or in June. The cold, damp 

 weather undoubtedly retarded their development so that the first 

 generation was ready to attack such boll weevils as were breeding 

 late in May and earl}^ in June. As only a few fields held tliis advan- 

 tage to the parasites, these fields naturally became much better 

 stocked vnth parasites, as has been pointed out in another paragraph. 



The summer and early fall months showed a sUglit deficiency in 

 rainfall and a slightly higher mean temperature — to such an extent, 

 however, that the season was considered dry, for the cotton did not 

 put on a very luxuriant foliage, and thus gave the sun plenty of play 

 on the fallen squares. The result is evidenced by the high percentage 

 of mortality from heat shown in the mortality tables. The increase 

 in parasitism may be ascribed to the same cause. 



The mean temperature of October, 1907, was normal in Texas, but 

 10° above normal in Louisiana. This warm season was followed by 

 a very sudden drop in temperature on November 11, the '^ norther" 

 lasting until the 15th. This caused the November mean in both 

 States to be 3° below normal (Texas 53° F., Louisiana 56° F.). In 

 both States during this one month the precipitation was 3 inches 

 above the normal. In northern Texas about 30 per cent of the adult 

 weevils were killed by cold. The temperature at Dallas ^ reached 

 14° on November 13, which was 11° colder than was experienced in 

 1906 and 21° lower than at any time in November, 1905. The boll 

 weevils were not prepared for tliis cold, as they were still in great 



1 The record was made both by the minimum thormomoter and the self-registoring thermograph at the 

 laboratory in East Dallas, and is a few degrees lower than the oflicial record at Oak Clifl, about 5 miles 

 to the west and across the Trinity River. 



16844°— Bull. 100—12 3 



