1909] Burrill, Epedemic of Silver Maple-Leaf Mite. 125 



several buds, in fact whole leaf sprays, all over under the micro- 

 scope to see if any were crawling about in early October, but 

 found none. Then I tested gall-covered leaves fallen to the 

 ground within a few days, — some of the galled leaves ripening 

 among the first and others hanging on with the last perfect leaves, 

 in fairly equal proportions ; also kept fresh leaves two or three 

 days on my desk till they were quite dry and shrivelled up. No 

 mites were thus forced out. On opening the galls, I found their 

 occupants quite alive. Is this not the key to preventive measures? 

 If the mites of the last generations of the season prove quite gen- 

 erally to stay in the galls, burning the leaves from time to time 

 as they fall in October will certainly reduce the numbers. 



There are two series of observations which throw doubt on 

 the complete efficacy of this measure, — the observations of Parrott 

 ( 1908) on their migration, and the other, the possibility of natural 

 parasites, as indicated by my observations. If there are parasites 

 to destroy them sufficiently, no further measure may be needed. 



Quoting Parrott first: "Shimer, 1869, suggested that it is 

 probable that they pass the winter, perhaps in the egg stage, on 

 the ground around the tree, and in early spring ascend the trunk. 

 Our observations on the hibernating habits of these mites 

 (P. qitadripcs and P. aceris-crumena) show that they seek pro- 

 tection just under the loose edges of the bark, about the stubbed 

 ends of broken twigs and limbs, and about scars of wounds caused 

 by hail and other agencies. For the past two years, the begin- 

 ning of the migration of these mites from the leaves to hibernat- 

 ing quarters occurred on July 12 and 10, respectively. On badly 

 infested trees, the mites have been seen assembled in such large 

 numbers on portions of the tree as to give a very distinct reddish 

 tinge to the bark. The mites are only to be found in scattering 

 numbers on the trunks of the trees near the ground. If it should 

 become desirable to spray for these mites, protection could un- 

 questionably be obtained, by the thorough treatment of the trees 

 with an efficient contact insecticide when the mites are migrating 

 in their largest numbers on the bark, or when they are established 

 in their winter quarters." 



Though not having seen such a migration myself, I have no 

 doubt that their traveling powers are great and for a creature so 

 tiny, .008 of an inch long, very fast, one traveling so fast from 

 end to end of the glass slide on my microscope that two of us 

 frequently lost track of her. But they show no such speed until 



