THE KED SPIDER ON COTTON. 33 



CLIMATIC CONTROL. 



Although, chmatic influences exert an immediate reducing effect 

 over hmited areas from time to time, the hardiness and the wide- 

 spread occurrence of the species insure the survival of sufficient num- 

 bers to reinfest locahties that may have been thus partially freed. 

 Owing to the fact that there is such a continuous succession of over- 

 lapping broods and that every stage from egg to adult occurs simul- 

 taneously, it is obvious that the most extreme weather factors can 

 not be expected completely to eradicate the pest. 



Climatic conditions do, however, influence the development of the 

 red spider to a marked extent, and this influence may be either detri- 

 mental or beneficial. In the occurrence of the seasonal cycle the 

 status of the red spider invariably undergoes a series of fluctuations. 

 Beginning in January (see fig. 8, p. 26) we find the pest maintaining itself. 

 In February no pronounced gain is ever made, although the develop- 

 ment of the species may undergo some slight advance or setback due 

 to weather. During March there is a gradual trend toward an opti- 

 mum, but the pest usually suffers one or more retarding checks from 

 adverse weather conditions. Through April and May the progress 

 of infestation is usually most rapid, so that by the 1st of June develop- 

 ment has nearly reached its maximum. Usually some time in June 

 or early July a sudden decimation occurs which reduces the status to 

 normal or below. This reduction is followed by a reaction, so that 

 some time between the middle of July and the last of August infesta- 

 tion again increases. From that time until October, usually, develop- 

 ment is subject to fluctuations varying considerably in extent, but 

 the autumn period is characterized by a rather abrupt diminution 

 until, by the end of November as a rule, the minimum again is reached. 



Rainfall. — During times of little rainfall and high temperature 

 reproduction goes on very rapidly; on the other hand, long, heavy 

 rains work havoc. In spite of the fact that the mites inhabit the 

 underside of the leaves, many are washed off by rains and others are 

 destroyed by the upward bombardment of sand particles. In fact, 

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

 some time, reduce, temporarily at least, the degree of infestation, 

 ^ythough a temporary reduction of the pest is occasioned by heavy 

 rains, many of the washed-off adults may be carried considerable 

 distances in the surface water at these times, only to revive upon 

 stranding, and to estabhsh new colonies remote from the scene of 

 their rearing, Tlius rain has the effect of greatly decreasing the per- 

 centage of infestation, while at the same time considerably extending 

 distribution. In one instanrxj a violet leaf, heavily coated with soil, 

 was (;xamin(;d and there remained, out of a re(;ent large colony, only 

 one female, one prim ary nymph, and numerous eggs. Of eight females 



