LIFE HISTORY IN GENERAL. 21 
early forms are sufficiently like the later and adult stages to be recog- 
nized, but more commonly there is sufficient difference in their appear- 
ance so that it is only by rearing them from stage to stage or by care- 
ful comparison of the different stages that it is possible to make out 
the correct life history. All, of course, pass through the egg and larval 
stages, and the last nymphal stage may be considered as correspond- 
ing to the pupal stage of insects in general. So far as has been deter- 
mined the eggs in the species affecting grains and grasses are deposited 
in the leaves or stems of the food plants of the larvae. The method of 
deposition has not been accurately noted in very many instances, but, 
for such as have been observed, it consists in the pushing of the eggs 
by means of the strong ovipositor into the margin of the leaf or into 
the spaces between the leaf and the stem so that the eggs are protected 
either by a covering of epidermis or by the thin leaf-sheath surround- 
ing the stem. A good example of the method of egg deposition is 
found in the case of the shovel-nosed leafhopper, winch is figured on 
page 66. The number of eggs deposited by an individual is known in 
a few cases and probably varies with different species. In some cases 
it must be considerable, as the rate of multiplication is rapid. The 
hatching of the eggs takes place either in a few days after the deposi- 
tion or, in the case of hibernating eggs, early in the following spring, 
and consists simply in the emergence of the larvae, the eggs being 
broken open at the end nearest the opening into which the egg has 
been forced. The molting occurs at uniform periods and consists in 
the shedding of the entire epidermal covering, tins usually remaining 
attached to the surface of the plant as a thin, transparent film. The 
insects increase in size and soon change from the light color of recent 
emergence to the dark intense color common to the species. The 
number of generations in each season is also a variable matter, but 
there are commonly two generations each season, in some probably 
three, and in a few it is known that a single generation occurs. This 
is, of course, an important factor in the economic importance of the 
species since each additional generation provides for an immense 
increase of the numbers of individuals and also makes the special 
conditions of culture for the crop on which it feeds much less effective. 
ECOLOGIC RELATIONS. 
The leafhoppers constitute one element in a very complex relation 
of plants and animals, including birds, mammals, reptiles, toads, 
insects, spiders, etc., and it is only by the recognition of this relation 
that we can offer any very adequate explanation of their proper 
place in nature, and of their importance in the economy of cultivation. 
Primarily they are associated with certain kinds of plants upon which 
they depend for their sustenance, and the abundance of leafhoppers 
will be affected, necessarily, by the abundance of the food plant and 
