August, '14] MCGREGOR: RED SPIDER COXTROL 331 



ordinarily, about June 15, and the larva are active among cotton mite 

 colonies. During September a large series of Chrysopa cocoons were 

 bred in the laboratory, and it is interesting to note that at least seven 

 species of parasites occurred so plentifully that over 48 per cent of the 

 Chrj^opids were attacked. 



During the month of July a species of thrips was observed to be 

 actively predaceous upon the red spiders. This species has been 

 identified as Scolothi-ips sexmaculata by ]\Ir. Morgan. It was exceed- 

 ingly abundant on infested cotton at Leesville, S. C, on July 25, of the 

 present year, and practically controlled some belated occurrences of 

 the pest in several observed fields. 



In addition to these five principal predators, there might be men- 

 tioned a Syrphid larva, several species of lady-beetles, and one or two 

 other thrips species which have been seen occasionally in or about red 

 spider colonies. It has not yet been determined whether there are 

 any internal insect parasites of the cotton mite. 



An extremely interesting association of ''cause and effect" seems to 

 have been established governing the fundamental origin of the great 

 fluctuation in degree of infestation occurring from j^ear to year. The 

 winter of 1911-1912 was the severest in South Carolina for many 

 years. Hence it might be expected that the following season would be 

 a mild one, from the standpoint of injury by the red spider, through 

 the assumed heavy mortality of the pest during the winter. On the 

 contrary, as has been stated before, the 1912 occurrence was the 

 severest on record. The only possible explanation appears to embrace 

 two suppositions. One is that the adult red spider is little susceptible 

 to extreme cold. The other is that the insect enemies of the mites 

 succumb much more readily to minimum temperatures than do the 

 mites themselves. Both of these hypotheses are sustained by all of 

 our observations. Naturally, then, a severe -^dnter is precisely what 

 would most favor the subsequent increase of the red spider through 

 the destruction of its insect enemies. Conversely, an abnormally 

 mild A^dnter, free from decidedlj- low temperatures, would furnish 

 conditions most favorable for the survival of the repressive species, 

 and the infestation for the following season would be mild. Thus, if 

 this rule is unerring, it becomes obvious that the influence exerted 

 indirectly upon the red spiders by pre-seasonal conditions is poten- 

 tially greater than that of other factors operating during the active 

 season. 



Remedial ]\Ieasures 



Prevention 

 From the abundant experience of the last three years we have been 

 forced to the conclusion that the eradication of the red spider must be 



