328 JOURNAL OF ECONOMIC ENTOMOLOGY [V'ol. 7 



of mites as nearly as could be determined. The time required for 

 the development of a generation varies with the prevailing tempera- 

 ture, etc., but ten days is the usual period necessary under summer 

 conditions. It is true that adult females continue to deposit eggs 

 intermittently throughout the winter, and many of these eggs, even, 

 may hatch during the occurrence of mild periods of winter weather, 

 but practically no instar development takes places after the middle 

 of October until the advent of vernal conditions. The extent of the 

 mortality arising from adverse winter conditions is largely conjectural. 

 It is very probable that most individuals of the immature stages are 

 killed during the winter, but a very high percentage of the mature 

 mites doubtless survive. 



Before becoming established on cotton, one or more preliminary 

 migrations usually occur. In the case of mites overwintering on cul- 

 tivated violets, they usually become so densely abundant on this 

 host that they cause the plants to wither and die to the ground by 

 early May. This forces a migration which carries the adult females 

 to a large variety of nearby plants — both wild and cultivated. These 

 secondary hosts in turn become overrun by mites and further migra- 

 tions become necessary. It is these later movements which, as a rule, 

 result in the discovery of cotton by the red spiders, and which most 

 frequently occur during the latter half of May. 



The appearance of red spider work on cotton is doubtless familiar 

 to most entomologists of the South, as it also is to many cotton planters. 

 The presence of the pest on cotton is first revealed by the appearance 

 on the upper surface of the leaf of a blood-red spot. As leaves become 

 badly infested they redden over the entire surface, become distorted, 

 and drop. The lower leaves usually are first attacked, but infestation 

 spreads upward until often only the bare stalk and one or two terminal 

 leaves remain. Such plants almost invariably die, but at any event 

 always fail to mature fruit. 



It may be said that large fields are probably never completely 

 damaged by this pest, but smaller fields frequently become wholly 

 affected. A thorough examination of all fields within one mile of the 

 center of Leesville, S. C, w^as made with a view of determining the 

 exact status of red spider infestation at one specific locality. In all, 

 ninety-nine fields were examined as carefully as possible, and about 

 74 per cent of the fields w-ere found to be infested to some degree. This 

 occurrence was perhaps more severe and more general than is usually 

 the case. Probably the most severe case in this locality (and typical 

 of a very heavy infestation) was one which had its origin in a large 

 clump of badly infested pokeweed stalks which grew at the edge of a 

 barnyard. The pest spread fan-like until it reached in one direction 



