jan. 27 ,1923 Inoculation Mechanics with Mosaic by Insect Vectors 281 
A study of these results seems to afford abundant confirmation of the 
fundamental fact involved—namely, that A. maidis acts as a vector of 
sugar cane or, more properly, grass mosaic. Experiments with positive 
and convincing results have been performed in the United States, Java, 
Cuba, Hawaii, and Porto Rico. The fact also appears to be established 
that while A . maidis prefers other grasses to cane as a source of food, it 
frequently migrates to the cane in large numbers. Weeding of a cane 
field is evidently a prime factor in bringing about this result, but the 
present writer has observed infestation of sugar cane by A . maidis in 
Florida in fields which are never weeded. The conclusions of investi¬ 
gators who disclaim that any practical importance attaches to this 
insect as a vector of mosaic is based on negative evidence, and therefore 
can not be held to controvert these facts in any way. Evidence has been 
adduced indicating that two other insects, Peregrinus maidis and Carolinaia 
sp., may transmit the disease. 
MECHANICS OF INOCULATION 
In an endeavor to gain some insight into the method by which insect 
vectors inoculate plants with sugar-cane mosaic, a number of individuals 
of several species of sucking insects were killed in situ , embedded in 
paraffin, sectioned and stained. The insects used were Aphis maidis , 
the known vector of mosaic; Peregrinus maidis , the corn leafhopper re¬ 
ported by Kunkel (5) to transmit mosaic from corn to com; and Draecu - 
lacephala mollipes, the large leafhopper which is so abundant on cane in 
this country, but which has failed to transmit the disease in repeated 
experiments. The latter insect was examined for comparative pur¬ 
poses, to determine if possible whether structural or functional feeding 
phenomena might inhibit its ability to transmit the disease. 
It was found that various methods had to be devised for killing the 
various insects in the feeding posture and holding them so during all 
the steps of fixing, dehydrating, infiltrating, and embedding. With 
Aphis maidis the process was found to be comparatively simple. A 
young leaf of corn with a quiet feeding colony was clipped from the plant 
and thrust into nearly boiling Camoy’s fluid. The insects were appa¬ 
rently killed almost instantly, before they could withdraw their setae, 
and it was only necessary to transfer the pieces of leaf with attached 
insects through the succeeding reagents with utmost care in order to 
prevent agitation of the liquids and consequent dislodging of the insects. 
In the case of Peregrinus maidis , a colony of adults and nymphs on a 
corn leaf was cooled for 20 minutes at a temperature of 21° F., and 
when the insects were rendered inactive by cold the leaf was plunged 
into the hot Carnoy’s fluid. A large percentage of these insects floated 
off but some remained attached. Specimens of Draeculacephala mollipes , 
comparatively large and heavy as well as active leafhoppers, were 
handled individually in small, moist chambers to the inside wall of which 
a piece of corn leaf had been pressed and held in a vertical position by 
means of gum arabic. The insect was gradually rendered inactive by 
cold while feeding, then suddenly pressed against the stationary leaf 
with the index finger and at the same instant covered with Carnoy’s 
fluid as hot as could be borne by the finger. Since these insects possess 
very large and thick feeding setae, as compared with aphids, and there¬ 
fore do not thrust the setae into the tissues to a great depth compared 
to the diameter of setae and weight of the insect, as in the case of the 
