LEAF-HOPPERS. 123 
in the plates (Plates IV-VIII). They are so numerous at 
times that every blade of grass harbors one or more, all engaged 
in drawing on the vitality of the plant by pumping up the sap. 
Prof. Osborn, formerly of Ames, Iowa, who has studied the his- 
tory of these insects very closely, in several of his papers de- 
scribes the astonishing number of such insects, and it is almost 
a wonder that any grass can survive their attacks. Nearly one- 
fourth, if not one-half of all the grass growing annually is de- 
stroyed by leaf-hoppers; this is a rather startling statement, but 
frequently only too true and borne out by facts. He has de- 
scribed these insects and their work so well that nothing better 
can be done than by quoting his words: 
“Following up the work indicated in the last bulletin we 
report some experiments with the hopper-dozer for leaf-hoppers. 
The larve of some species of the leaf-hoppers, notably Delto- 
cephalus debilis and D. wninucus, appeared in great numbers upon 
the college campus about the eleventh of May. About two weeks 
later a frame six feet long and about two and one-half feet high 
was mounted upon runners so that it made an angle of about 
sixty-five degrees with the horizontal, and was covered with heavy 
paper which was then coated with coal tar. The runners were 
about one and one-fourth inches high so that the lower edge of 
the frame would scrape the grass when it was pushed forward 
by means of two handles so fastened that the operator could 
walk behind. This machine was somewhat unsatisfactory. The 
insects would be caught upon the lower part of the dozer and 
be brushed off on the grass together with the tar, which not only 
prevented our knowing the results we were getting, but injured 
the grass to a slight extent for feeding purposes. It was also 
noticed that many of the insects upon rising in front of it would 
swerve from its path too quickly to be caught by its motion. 
However, many of the insects were destroyed, and an unex- 
pected result was the multitude of mites (Bryobia pratensis) cap- 
tured, probably being thrown upon the dozer by the backward 
spring of the plants upon which they were feeding, from beneath 
a wire fastened two or three inches before the dozer for the pur- 
pose of scaring up the leaf-hoppers. Another form of the dozer 
was next tried. A piece of sheet iron, eight and one-half feet 
long and two feet wide was coated on the upper side with coal 
