26 



BULLETIX 416^ U. S. DEPAETMEIS^T OF AGEICULTUEE. 



A'p'proxhTnate date of reduction in numbers. — During each of the four 

 years of the red-spider investigation there has occurred at some time 

 of the season a sudden reduction in the numbers of the pest due to 

 the abundance of natural enemies. Unfortunately, this is not general 

 and simultaneous throughout the South. Furthermore, the mite 

 reduction occurs at different times from season to season. In 1911 it 

 did not take place in central South Carolina until about the 1st of 

 September, whereas in 1912 the pest was controlled as early as July 10. 

 In 1913, July 20 marked the approximate date of decimation, and in 

 1914 the phenomenon occurred about July 20. For the four seasons, 

 the average date of the reduction of the red spider by its insect ene- 

 mies is found to be about July 15. 



Following these seasonal decimations the mites are often reduced 

 almost to extinction, which naturally reacts against the predatory 

 species in due time, and in their absence a secondary impetus is 

 usually noted in the development of the red spider. These second- 



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Fig . S.— Cxirve representing the 4-year composite seasonal status of the red spider in central South Caro- 

 lina. The depression of the line in June represents the decimation arising through the activity of 

 predatory enemies. (Original.) 



ary occurrences seldom result in serious infestations, but have the 

 result of restoring somewhat the status of previous cases. This 

 numerical revival may be looked for usually between the middle and 

 last of August in South Carolina. (See fig. 8 for seasonal status curve.) 



FaU and early winter status. — In parts of the world where the red 

 spider hibernates the mites prepare to leave their host plants at the 

 approach of winter and seek shelter in the ground or under the bark 

 scales at the base of the trunk or stem of trees. In South Carolina, 

 the mature mites assume the characteristic orange-yeUow color with 

 the arrival of late faU. 



The mites which live through the winter are to be found usually 

 on the basal leaves of a few dooryard plants, such as English violet, 

 hollyhock, strawbeiTV, and mustard, and upon several native species 

 of weeds, etc., which offer green leaves. Every stage, from egg to 

 adult, of both sexes has been repeatedly encountered during winter. 

 The immature individuals produced in brief intervals of favorable 



