THE RED SPIDER OX COTTOX. 



13 



XATl'RAL COXTRoLr.INC ACJEXCIES. 



In both the seasons of 1911 and 1912 red-spider occurrence was 

 most severe throughout July and early August. The last two weeks 

 of August in both cases, however, witnessed so great a reduction of 

 the pest that by the end of that month it was hardly noticeable, as 

 a rule. This phenomenon, indeed, happens suddenly, and the agen- 

 cies Avhich work to produce it are unquestionably of great economic 

 value. The ageing and toughening of the leaves at about this time 

 may cause many mites to desert the cotton for other plants, but 

 another factor of probably much greater importance is the increased 

 abundance of several species of insect enemies which seem to gain 

 dominance at just this time. 



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Fk;. '.I. — A severe example or red-spider work in a cotton field. .Nearly all i)lants in tlie 

 , forejrround are in the condition sliown in flaure S. The source in tliis case was certain 

 pokoweed stalks srowin*? in the weed border seen in the upper right-hand corner of 

 illustration. (Orisrinal.) 



CLIMATIC INFLUENCES. 



As before mentioned, climatic conditions exert a marked influence 

 upon the welfare of the pest. During times of little rainfall and 

 high temperature reproduction goes on by leaps and bounds; on 

 the other hand, long, heavy rains work havoc to the red-spider 

 population. In spite of the fact that the red spiders inliabit the 

 under.side of the leaves, many are washed off by rains and many more 

 are destroyed by the upward bombardment of sand particles, which 

 may always be seen coating the lower leaves after storms. In fact, 

 it appears true that a few heavy rains, especially if they continue 

 for some time, accomplish as much toward controlling the pest as 



