30 



BULLETIISr 416;, U. S. DEPARTMENT OF AGEICULTURE. 



Table V. — List of important spring weed hosts of the red spider, Batesburg, S. C. 



Stachys arvensis. 

 Chenopodium botrys. 

 Sida rhombifolia. 

 Geranium carolinianum. 

 Trifolium repens. 

 Sonchus as per. 

 Vicia sativa. 

 Taraxacum officinale. 

 Gnaphalium spathulatum. 

 Rumex obtusifolius. 

 Oenothera laciniata. 

 Oxalis stricta. 

 Panicum scoparium. 

 Helianthus annuus. 

 Convolvulus sp. 

 Plantago lanceolata. 

 Croton texensis. 



Rumex crispus. 

 Stellaria sp. 

 Solanum carolinense. 

 Solanum nigrum. 

 Ipomoea purpurea. 

 Passiflora incarnata. 

 Lechea villosa. 

 Brassica campestris. 

 Wild grass. 

 Rubus sp. 



Phytolacca americana. 

 Ambrosia artemisiae folia. 

 Amaranthus hybridus. 

 Datura stramonium. 

 Erigeron sp. 

 Xanthium americanum. 



WATER DISPERSAL. 



For a long time investigators of the red spider found it difficult to 

 explain why isolated infestations existed in fields comparatively 

 remote from the source of dispersion. It has been known for years 

 that heavy rains dislodge many red spiders, and it has been taken 

 for granted that these mites were destroyed. We have estabhshed 

 the fact, however, that 9 hours' submergence in water is necessary to 

 cause the death of red spiders. Beaten to the ground by the heavy 

 downpour of rains, countless thousands of mites are carried along in 

 the surface water and may even find their way into the smaller 

 creeks. Provided the red spiders are not iajured, they may revive 

 and become estabhshed many rods, perhaps, from the scene of 

 detachment. Table VI presents the data on submergence of mites 

 and the resulting mortahty. 



Table VI. — Submergence and red spider mortality , Batesburg, S. C, 1914- 



Experi- 

 ment 

 No. 



Ex- 

 posure. 



Inter- 

 val 



before 

 exami- 

 nation. 



Mor- 

 tality. 



Condition of in- 

 dividuals not 

 recovering. 



Experi- 

 ment 

 No. 



Ex- 

 posure. 



Inter- 

 val 

 before 

 exami- 

 nation. 



Mor- 

 tality. 



Condition of in- 

 dividuals not 

 recovering. 



1 



Hours. 

 24 

 24 

 24 

 24 

 12 



7 



2.5 

 17.5 



8 

 10 



Hours. 



12 



12 



3 



3 



2 



15 



Per 

 cent. 



100 M n.r>firatp.d . 



11 



12 



13 



14 



15 



16 



17 



18 



19 



Hours. 

 12 



9 



10 

 11.5 



6 



8.25 

 10.25 



9 



7 



Hours. 

 4 

 3 

 6 

 6 

 10 

 4 

 6 

 4 

 8 



Per 

 cent. 

 100 

 100 

 100 

 100 



50 



83 

 195.3 

 100 



95 





2. 



100 

 100 

 100 

 100 



1 7(1 



Do. 



Shrunken. 



Do. 



Do. 



Macerated. 



Shrunken. 

 Shriveled. 

 Shrunken. 



Do. 



3 





4. 



Do. 



5 



Do. 



6. 







4 n 





8 



5 

 6 

 6 



100 

 50 

 100 





9 





10 





1 A minute air bubble, about which were some of the mites, remained in the vial. 



