214 Acarology 



Type. Acarus latens Mliller, 1776 (= Trombidium lapidum Hammer, 

 1804) 



19. Platytetninychus Oudemans, 1931 



Type. Tetranychus gibbosus Canestrini, 1890 



20. Pseiidobryobia McGregor, 1950 



Type. Pseiidobryobia bakeri McGregor, 1950 



21. Septcmychus McGregor, 1919 



Type. Tetranychus tiimidus Banks, 1900 



22. Schizotetranychus Tragardh, 1915 (= Stigmaeopsis Banks, 1917 = 



Divarinychiis McGregor, 1930) 

 Type. Tetranychus schizopus Zacher, 1913 



23. Simplinychus McGregor, 1950 



Type. Neotetranychus buxi Garman, 1935 



24. Tetranychina Banks, 1917 (= Tenuicrus Womersley, 1940) 

 Type. Tetrany china apicalis Banks, 1917 



25. Tetranycopsis Canestrini, 1890 



Type. Tetranychus horridus Canestrini and Fanzago, 1876 



Discussion: Metatetranychus idmi (Koch) [known in this country 

 as Paratetranychus pilosus (Canestrini and Fanzago)] can be used for 

 illustrating one type of spider mite biology. The mite passes the winter 

 as eggs, which are deposited on the branches and twigs, are bright red, 

 and may be so numerous as to give the branches a reddish appearance. 

 In the northwestern United States these eggs hatch in the spring, when 

 the new leaves are appearing. The egg, which is stalked but without 

 the guy wires found on legs of M. citri (McGregor), splits around its 

 equator for most of its circumference, a small portion being left as a 

 hinge. The upper half, or lid, is lifted by the six-legged larva, which 

 crawls out, the lid usually springing back to its original position. The 

 small, bright-red or orange larvae swarm to the young leaves and at 

 once begin feeding. After a period of feeding, during which the larva 

 moves about to some extent, it settles down, usually on the under side 

 of the leaf near a vein or midrib, and remains quiescent for a time 

 about equal to the feeding period. Afterward the skin becomes smooth 

 and glossy in appearance and finally turns pearly white, an indication 

 that the larva has loosened itself from the new skin underneath. Within 

 a few hours the skin splits transversally across the dorsum, between 

 . the second and third pair of legs, and the eight-legged protonymph 

 emerges. The molted skins remain adhering to the leaf, and if numer- 

 ous enough give the leaf a silvery appearance. The protonymphal stage 

 is shorter than the larval stage, and the feeding and quiescent stages 

 are repeated. The mite then molts and becomes a deutonymph, which 



