MECHANICS OF INOCULATION WITH SUGAR-CANE 
MOSAIC BY INSECT VECTORS 1 
By E. W. Brandes 
Pathologist , Office of Sugar-Plant Investigations , Bureau of Plant Industry , 
United States Department of Agriculture 
INTRODUCTION 
It has been demonstrated with practical certainty that the only 
method for natural spread of sugar-cane or grass mosaic is through the 
agency of insects, acting as simple vectors or possibly as intermediate 
hosts. 
It was established by the writer (i) 2 that Aphis maidis is able to 
transmit this disease. A considerable amount of confirmation of this 
result has now accumulated and notwithstanding some early skepticism 
it appears to be generally accepted. The mere fact of its ability to 
function as a vector, however, has been regarded by several investigators 
as of no great practical significance on account of the supposed scarcity 
of the insect on sugar cane. It was even suggested that A . maidis never 
occurred on sugar cane and that when colonized on cane plants the 
insects would die. On the contrary, other investigators have suggested 
that A. maidis is responsible for much of the natural transmission of 
mosaic in commercial plantings of sugar cane. In view of these diver¬ 
gent opinions, a review of experimental work on this subject is desirable, 
REVIEW OF EVIDENCE ON INSECT TRANSMISSION 
Taking up the published work in chronological order, Brandes (i) 
announced that Aphis maidis is able to transmit the disease to healthy 
plants after a previous feeding on diseased plants. It was stated in 
this paper that all species of insects used in the experiments were known 
to feed on sugar cane and that A . maidis in particular had been reported 
on sugar cane from practically all sugar-cane countries. Thus it was 
assumed that a certain amount of natural transmission in the field is 
traceable to this insect. The belief was expressed, however, that 
natural transmission is not restricted to A. maidis . 
Smythe (8 ) 9) carried on a large number of experiments on insect 
transmission of mosaic at the Insular Experiment Station at Rio Piedras, 
Porto Rico. He reports successful transmission with a variety of insects. 
His results, however, are not convincing. The small number of experi¬ 
ments which he reports as successful are questionable, since in some 
cases his test plants were transplanted to an open field and left for a 
period greater than the minimum incubation period for mosaic before 
showing symptoms. 
Tower (jo), also working in Porto Rico, got only negative results 
from experiments in which he used sucking and chewing insects. 
1 Accepted for publication Nov. 17, 1922. 
* Reference is made by number (italic) to “ literature cited,” p. 283. 
Journal of Agricultural Research. Vol. XXIII No a 
Washington, D. C. j an . 27,1923 * 
Key No. G-a 7 a 
(279) 
