16 



CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



their leaves, any foliage injury will reduce the vitality of the tree, and 

 consequently the size of the fruit, even if it does not cause the leaves 

 to drop off. 



LIFE HISTORY 



There are three species of orchard-infesting red spiders in the Pacific 

 Northwest. These differ somewhat in their habits, and somewhat 

 different methods must be used to control them. All are of European 

 origin. 



The common red spider or 2-spotted mite (Tetranychus telarius L.) 

 (fig. 17) may be recognized most easily by the quantity of webbing it 

 spins, which often collects dust and gives the foliage a very dry and 

 dusty appearance. This species passes the winter in the adult stage 

 in leaves and trash on the ground. In the 

 spring the surviving mites migrate into the 

 trees, first attacking the foliage nearest the 

 ground and gradually extending their oper- 

 ations to cover the whole tree. The mites 

 are usually greenish or yellowish while feed- 

 ing, often with two dark spots on the body, 

 and reddish or orange when migrating in the 

 fall to their hibernating places. The eggs, 

 which are almost colorless, are laid in the 

 webbing. The young are similar to the 

 adults in appearance, except that they have 6 

 legs instead of 8. They develop from egg to 

 adult in a week or 10 days, and there are 

 several generations in a year, which makes it 

 possible for the mites to become exceedingly 

 numerous in one season. This species thrives 

 on a large variety of trees, shrubs, and herba- 

 ceous plants, and is often a serious pest in 

 greenhouses. 



The European rea mite (Paratetranychus 

 pilosus C. and F.) lays bright red overwinter- 

 ing eggs on the twigs and branches of fruit 

 trees (fig. 18), and when these eggs are nu- 

 merous they are very noticeable as reddish 

 patches on the bark. They are also found in the calyx end of 

 mature apples (fig. 19). These eggs hatch in April just before the 

 blossoms open. The mites feed on the foliage, usually on the 

 underside, and spin very little webbing. They are more easily seen 

 than the common red spider, being velvety or brownish red, with 

 conspicuous, whitish, curved spines on the back. During the summer 

 the eggs are laid on the leaves, and there are 7 or 8 generations in a 

 season. This species is very seldom found on anything except decid- 

 uous fruit trees. 



The brown mite or clover mite (Bryobia praetiosa Koch) (fig. 20) 

 also passes the winter in the egg stage, the eggs being very similar to 

 those of the European red mite and not distinguishable from them 

 with the naked eye. They hatch at about the same^ time in the 

 spring, and the habits and life history of the two species are much 

 alike. The brown mites spin no webbing and usually congregate in 

 roughened places on the twigs and branches during the day, migrating 

 to the leaves at night to feed. This habit of feeding at night and the 



Figure 17. —Common red spider: 

 A, egg; B, adult. Sixty-four 

 times natural size. 



