122 College of Forestry 
of July (first blossom in 1917 seen on July 13), and the 
maximum was not reached until the first week in August. 
A comparison of the data collected during these four years 
makes unescapable the conclusion that one can foretell the 
relative abundance of any one of a number of species, not in 
terms of the calandar date, but of the condition of the blos- 
soms which furnish them food. Thus the blossoms of wild 
spirea (and doubtless other blossoms sought by insects) act 
as an indicator by which we may determine the seasonal 
distribution of certain insects depending upon them for food. 
In a sense the condition of the blossoms and the relative 
number of certain insect visitors are co-ordinated. Perhaps 
a more exact statement of the real relations might be made 
as follows: The relative abundance of the insect in the case 
of many lepturids and of some others, is really determined 
by the relative advancement of the season, and this is indi- 
eated by the condition of the blossoms upon which the insects 
depend for their adult food. In other words, while this 
synchronism works to the advantage of the insect and doubt- 
less also to that of the plant, we cannot assume that the rela- 
tion of cause and effect exists, but must rather look upon 
the two as separate phenomena both of which are dependent 
upon the same cause, the advancement of the season. Evi- 
dence leading to this conclusion will be found later, in the 
notes on a number of species. 
In the following tabulations all of the insects mentioned 
were taken from wild spirza blossoms except those of the 
first two weeks and a few in the third week of July, 1917, 
which are from the blossoms of wild blackberry. As soon as 
the spireea blossoms appeared in any numbers, the pollen- 
eating insects seemed to desert the berry blossoms and to feed 
nearly exclusively upon those of the spirea. Thus the berry 
blossoms, although not the favored food supply of a number 
of these insects, seem to serve to tide the insects over till a 
better source is available. It is worthy of note in this con- 
nection that several of the lepturids had passed their maxi- 
mum before the appearance of the richer supply of pollen, 
but the greater number of individuals, even of these species, 
