18 LEAFHOPPERS AFFECTING CEREALS, BTC. 
in Mexico, Central America, and the West Indies. If we note the 
bare half-dozen species known in Europe, and the further fact that 
nearly all the species drop off as we pass northward in either region, 
we can best incline to the belief that this genus is essentially tropical 
or at least subtropical in its origin and that its dispersal has been 
northward into the northern United States and Canada and probably 
by an African route into southern Europe. If such be the case, it 
is interesting to note that a separation into certain types within the 
genus must have occurred before the migration, as the Kuropean 
species Agallia venosa Fall. and A. puncticeps Germ. parallel very 
nicely our groups of which Agallia sanguinolenta and A. 4-punctata 
Prov. are typical examples. Such a derivation possesses peculiar sig- 
nificance in connection with certain habits and life-history features, 
especially in modes of hibernation, and some of these may prove of 
fundamental importance in connection with efforts toward practical 
control. 
Again, we have in Athysanus exitiosus Uhl. a species which has in 
all probability spread over the United States in very recent times, 
possibly even within the last half century, and which almost cer- 
tainly had its dispersal from a tropical or subtropical center. 
Another similar case, discussed more fully in another place, is 
found in Dreculacephala reticulata Sign., which is even now probably 
working gradually northward, though it seems from its present dis- 
tribution to have a pretty definite climatic restriction. 
SPECIES PRINCIPALLY CONCERNED IN DESTRUCTIVE ATTACKS. 
Serious outbreaks upon different cereal crops are to be charged 
to a few species, notably Deltocephalus inimicus, D. nigrifrons, Cica- 
dula 6-notata, Dreculacephala reticulata, D. mollipes, Athysanus exi- 
tiosus, and Phlepsius irroratus, all of which are among the most 
important from an economic point of view. There are numerous 
other species which attack these crops, especially various grasses 
and forage crops, the habits of which are important, but whose 
injuries individually are of less consequence than for the species 
just cited. In the case of the wheat crop serious attacks in America 
are to be charged against the few species above mentioned, all of 
which, except one, are native to this country; hence, not original 
wheat-feeding species. They seem, however, to find this plant an 
attractive food and where conditions permit will gather upon it in 
very destructive numbers and cause serious injury. Comparatively 
speaking, very few of the old-world species in this group have fol- 
lowed the wheat plant to this country, and there is only one species 
common to both Europe and America that can be considered a pest. 
Whether this species has been introduced since the introduction of 
wheat in this country is a question that probably can not be deter- 
mined, since it is now so widely distributed that there is little evi- 
