October, '10] weldox on mites 431 



for eggs was made. The search resulted in not finding a single one. 

 A large abundance plum tree, at the base of which myriads of the mites 

 entered the soil in August, served as an observation place until Octo- 

 ber, when the work ceased until spring. On the 23rd of March the 

 tree was again visited, and an examination of the soil near the crown 

 was made for mites which it was thought had surely hibernated there 

 over winter. Clod after clod was broken, myriads of the dead mites 

 were found, and the search became discouraging. Finally a clod 

 which was quite moist, and which had probably retained its moisture 

 all winter, was broken into, and there in a tiny soil cavity was a nest 

 of only half a dozen lively little red mites, which had survived through 

 severe winter weather, at a depth of 1.25 inches beneath the surface of 

 the soil. The striking fact that where millions had entered the soil in 

 the fall, only a very few individuals survived, was attested by the tre- 

 mendous lot of dead ones encountered during the search, and only a 

 half dozen live»ones. Truly it was a case of the survival of the fittest. 



Summer Habits of T. bimaculatus. — This is the only species of 

 Tetranychus that I have found feeding upon orchard trees. The close 

 association of this species with Bryobia pratensis has njade it very 

 difficult for the orchardists to distinguish the one species from the 

 other. T. himaculatus has been commonly found in the orchards on 

 apple, plum, prune, peach, pear, cherry and almond trees. Most of 

 our shade trees seem subject to their attack, and small fruits are 

 quite often severely injured. Especially have they been abundant on 

 raspberry bushes, and some of the raspberry growers have attrib- 

 uted not only the failure of their fruit crop, but also the death of 

 many bushes to the attack of this little pest. 



The season during which this pest becomes serious is fortunately 

 short. It is seldom that their injury becomes great until the hot 

 weather of July, and while a few commence work quite early in the 

 season, it is not usual to see them in great numbers until the excessive 

 heat of midsummer accelerates their development. Often the orchard- 

 ist is hardly aware of their presence until the latter part of July, 

 when he suddenly notices the foliage of his trees turning yellow, and 

 at this time he may also witness a wholesale migration of the little red 

 pests to the ground, where every clod turned over reveals the hiding 

 place for hundreds of them. Slowly they make their way into the soil 

 to a depth of presumably never more than two inches, where condi- 

 tions will probably be favorable for at least a few of them to survive 

 the winter. On the 26th of July this season, the first downward migra- 

 tion of mites was noticed in two orchards near Grand Junction, and 

 the soil for several feet on every side of infested trees was alive with 

 them. 



