\ New York AGRICULTURAL EXPERIMENT STATION. 299 
INTRODUCTION. 
The apple has many insect enemies, and hardly a year passes but 
that a species develops in sufficient numbers to alarm the fruit- 
growers of this State. The rapid rise of a common insect, from 
comparative obscurity to a position of first prominence within one 
season, followed in turn by its almost complete disappearance in as 
short an interval of time, is one of the most interesting phases of 
animal life. Insects are especially capricious and their behavior 
in this respect is not entirely unexpected; but that a mite which 
had no reputation in this capacity and whose presence was entirely 
unsuspected, and not an insect, should so completely overrun our 
apple orchards brings surprise to many fruitgrowers. This mite 
has been on the increase during the past four years, and by its 
abundance and its conspicuous work on apple foliage, has caused 
quite a little apprehension among apple growers. Added interest 
has been given to the progress of this creature because of the grow- 
ing importance of spray injuries, with which the work of the mite 
has been confused. In conducting the investigation to determine 
the cause and means of prevention of the peculiar diseased condi- 
tions of apple leaves it was found necessary to include the pear, as 
several species of mites are common to both fruits. 
In the study of the mites subsisting upon apple and pear leaves, 
four species, all of foreign origin, have been distinguished, the more 
important being Eriophyes pyri (Pgst.) Nal., long recognized as a 
destructive pest of the pear. This group of plant-inhabiting mites 
is little understood, and that there may be a greater appreciation 
of them, especially of the species under discussion, an introductory 
review is given of the Eriophyidae as a preliminary to a more ex- 
tensive treatise. 
Special acknowledgments are due to Dr. Alfred Nalepa, of 
Vienna, who has verified all the determinations and has furnished 
copies of his valuable monographs upon the Eriophyidae, which 
have been freely consulted. Prof. J. H. Comstock of Cornell Uni- 
versity has kindly given much advice upon methods of making per- 
manent mounts and has allowed the use of his library for reference 
purposes. Dr. Karl Rechinger, Vienna, and Mr. Edward T. Con- 
nold, St. Leonards-on-Sea, England, contributed a number of pho- 
