136 
tude and climate, between northern and southern Illinois; hence 
each species must be studied in different parts of the state. The 
most important species — that is the most abundant ones — are not 
the same in all parts of Illinois, and the relative importance of the 
various species must be made out for each region separately. The 
unexplained sudden disappearance, several times noticed by us, of 
nearly the whole grub population of badly infested fields before 
their transformation to the pupa, suggests the occurrence among 
these insects of contagious diseases — a supposition borne out by sev- 
eral field and insectary observations ; and the whole subject of their 
bacterial and other fungus parasites consequently invites attention. 
The enormous effect of the rapid multiplication, under favorable 
conditions, of certain insect parasites — a hymenopterous enemy, 
Tipliia inornata, especially — requires a critical and complete study 
of the life history of these parasitic insects also, especially as there 
is some probability that we shall be able to increase their efficiency 
by artificial measures. 
No one has heretofore undertaken to work out to a finish this 
difficult but highly important economic problem, and our present 
knowledge of the white-grubs is a patchwork of fragments, contrib- 
uted by a considerable number of observers working on various 
species and in different parts of the country. The nearest approach 
thus far made to a continuous investigation of the subject was car- 
ried on in this office in the years of 1886 -1890, and its results were 
published in 1891 in Volume III. of "Insect Life."* 
They were also incorporated, with some later studies, in the 
Eighteenth Report of the Illinois State Entomologist, printed in 
1894. In the year 1906 I finally began what I now hope may prove 
to be a steady and comprehensive study of this problem for the 
state of Illinois ; and I have now to report some of the first results 
of this work, which I have incorporated, however, with other data 
and conclusions in a way to give us a fairly full synopsis of the 
present state of our knowledge, and a clear view, consequently, of 
its deficiencies. 
The Economic Species. 
The kinds of white-grubs common enough in Illinois to attract 
attention because of their injuries, belong, so far as we now know, to 
nine species, although it is likely that this list would be longer if the 
injurious grubs of southern Illinois were as well known to us as 
those of the central part of the state. Besides these nine injurious 
*"On the Life History of tlie Wliite-grubs." By S. A. Forbes. Insect Life, Vol. III., No. 
5, pp. 239-245. 
