20 LEAFHOPPERS AFFECTING CEREALS, ETC. 
any wide sense are unknown for any of the species. There has been 
observed in many cases a distinct tendency to gather at night around 
conspicuous lights, and while it is not known whether all of the species 
are thus attracted, so many different ones have been noted as being 
attracted by artificial lights that we may fairly presume that the habit 
is quite general. An instance was reported to the writer by Prof. 
Stedman, formerly of Missouri, with accompanying specimens of 
Dreculacephala mollipes, to the effect that this species gathered about 
lights at Columbia, Mo., in such numbers that they could be gathered 
up by the bushel. We have noted many instances of the appearance 
of the various species, including practically all of the more common, in 
rooms which are brilliantly lighted. This habit is sufficiently pro- 
nounced that it may be utilized for the purpose of collecting and 
destroying the adults before they have deposited eggs, although it has 
not been experimented upon to such an extent as to warrant any 
conclusion. 
An interesting case of the assembling of these insects at Urbana, 
Ill., has been reported to me by my son, H.T. Osborn. He states that 
on the evenings of October 9 and 10, 1909, he noticed a cloud of insects 
about a cottonwood tree and upon examination found that these 
consisted largely of the Phlepswus vrroratus. These were so numerous 
that he caught a net full, but no evidence of egg-depositing or of a 
particular object in this assembling was noticed. 
The winter condition of these species varies, some of them passing 
the colder months as adults and in these egg-laying occurs in early 
spring; others hibernate as partially grown nymphs; and in other 
species, particularly the grass-infesting forms, hibernation is appar- 
ently common in the egg stage. This matter of hibernation is of the 
greatest importance, especially in connection with methods of control 
based on the treatment that is possible in late autumn and in early 
spring. It also is related to the effects of climate, as in the case of 
those forms which become active in mild weather during winter and 
are thus exposed to conditions which may affect their survival and the 
consequent injuries the following season. Another general habit 
which is of importance is a tendency to dispersal from one kind of 
plant to another during the last nymphal stage. It has been noticed 
that many species which seem to be very closely restricted "to partic- 
ular plants in the earlier nymphal stages, during the last nymphal 
stage scatter freely to different kinds of plants, showing a distinct 
disposition to vary their diet. 
LIFE HISTORY IN GENERAL. 
All of the species of leafhoppers pass through a series of molts, 
usually four or five in number, and in these various stages they show 
a gradual progression toward the adult form. In some cases these 
