8 



BULLETIN 1035, U. S. DEPARTMENT OF AGRICULTURE. 



occurring- during the red spider season also interfere with the regu- 

 larity of the generations. Activity of the red spider usually com- 

 mences during the latter part of August and ceases the first part of 

 April, giving an active season of about 240 days. The average dura- 

 tion of. the life cycle is 14.2 dsijs, which would give 17 generations. 

 This would be true where no interruptions due to climatic conditions 

 occurred, and when no other factors interfered with the normal activi- 

 ties of the mites in the field. 



Shedding of the foliage. — During the winter months the foliage 

 may be termed " dormant," no new growth being present on the trees. 

 Usually during the latter part of March and April the avocado com- 

 mences to bloom and the older leaves, which have served their purpose 

 to the trees, commence to fall. With the shed leaves many mites are 

 lost and do not regain positions on the trees. During the latter part 



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Fig. 4. — Curves showing 2-year composite seasonal status of the avocado red spider iu 

 southern Florida. The decimations arising through the amount of precipitation are 

 the most important controlling factor in the activities of the species. 



of April very little old foliage is present and a remarkable reduction 

 of red spiders is apparent. A few old leaves, however, always re- 

 main on the trees until the newer growth has hardened and thu- 

 enable the red spiders to remain continuously on the trees and to in- 

 fest the newer growth when it hardens. 



Climatic control. — Climatic conditions existing in Florida influence 

 the development and activity of the red spider to a marked degree. 

 This particular species, as has already been stated, confines its depre- 

 dations to the upper surface of the foliage. The species so working 

 is exposed to the weather conditions. Hence during the period of 

 the life cycle or seasonal cycle there is a series of fluctuations in 

 numbers. In April, as the rainy season approaches, the red spider 

 barely maintains existence. (Fig. 4.) During the months of June. 

 July, and August no pronounced gain is made, but toward the latter 

 part of October the avocado ceases to produce new growth, the red 

 spiders commence to make their appearance in greater numbers, and 

 increase, during November and December. They usually reach the 

 maximum number during January and February, and decrease 

 again toward March. Precipitation is the one climatic factor im- 

 portant in reducing the red spiders during the spring and summer. 



