GREENHOUSE RED SPIDER. 155 



FOOD PLANTS. 



Tetranychus bimaculatus is very cosmopolitan in its feeding habits, 

 having been listed by McGregor as feeding on 183 species of plants, 

 55 per cent, of which were cultivated, in the southeastern part of the 

 United States. Much confusion has arisen because of the large number 

 of host plants and the variability in color of mites feeding on these different 

 plants. New species have been described based upon these color varia- 

 tions, but they have been discarded by later workers as synonymous. 



Under New England conditions of climate the red spider as a rule does 

 not seriously damage plants except those which are usually grown in 

 greenhouses. A few exceptions to this statement may occur near badly 

 infested greenhouses or during very dry seasons. As this paper has to 

 deal with greenhouse control, only those plants found most often infested 

 in, and in the vicinity of, greenhouses will be enumerated. 



The greenhouse vegetables most subject to attack are (1) cucumbers, 



(2) egg plants and (3) tomatoes. 



Cucumbers grown under glass in the market-garden district of Boston 

 are rarely exempt from the attacks of red spiders. These plants are first 

 attacked when only two leaves have unfolded, and injury continues until 

 the death of the plant, which in the majority of cases is due primarily to 

 the removal of chlorophyll from its leaves by the mites. Egg plants, 

 although very susceptible to attack, are not generally grown in the vicinity 

 of Boston. Greenhouse tomatoes appear to be practically immune from 

 red spider injury except when very young. Several times the writer has 

 seen a greenhouse containing approximately 1,500 full-grown cucumber 

 plants, with a row of tomatoes planted at each end of the house. The 

 cucumber plants were rapidly dying from the injuries caused by millions 

 of .red spiders, while the tomatoes remained unaffected. This was an 

 extremely severe infestation, and shows to what extent greenhouse to- 

 matoes are immune. Almost all weeds found in infested greenhouses 

 harbor mites, and if not destroyed are liable to infect a following crop. 



The greenhouse flowers subject to attack are (1) roses, (2) violets, 



(3) sweet peas, (4) carnations, (5) chrysanthemums and (6) many others 

 of minor importance. 



In floriculture perhaps the most important infestations occur on roses 

 and violets, with sweet peas, carnations and chrysanthemums next in 

 order. Usually a very large number of widely differing plants are grown 

 in a florist's greenhouse, and many of these will become more or less 

 seriously infested by the migration of mites from one or more of the above- 

 mentioned plants. However, these infestations are usually not of great 

 importance. 



The plants in the vicinity of greenhouses subject to attack are (1) 

 beans, (2) egg plants, (3) celery, (4) tomatoes, (5) strawberries, (6) clover, 

 (7) grasses and (8) weeds. 



Plants subject to attack which are found near greenhouses may serve 



