140 College of Forestry 
It would seem then, that in the case of an insect feeding 
upon pollen or honey, or both, which has shown a preference 
for that derived from the spirzea blossom, a curve showing 
its numerical abundance upon this flower at fixed intervals, 
should represent its seasonal distribution. The accuracy of 
this curve would depend upon the factors already mentioned. 
The larger the number of insects taken at each period and 
the larger per cent collected of those actually out, the more 
reliable will be the curve. It is apparent that when the 
number of specimens of a consistent visitor to spireea is great 
enough, quantitative data furnishes material for the con- 
struction of a reliable curve showing seasonal numerical 
distribution. 
A number of curves from such data are shown in the 
accompanying figure. It will be seen that typically they fall 
into two general classes dependent upon the habits and mode 
of life of the insect. In cases of species which live as indi- 
viduals (7. e., not in colonies), the curve typically shows an 
even rise, which may be either gradual — such as Allantus 
bastlaris — or sudden — such as Leptura canadensis — until 
a maximum is reached. This maximum may be held for 
several weeks followed by regular decline, as in Leptura 
proxina, or a more or less gradual drop may follow the 
maximum immediately, as in the curves of T’ypocerus velu- 
tinus and Leptura canadensis. The irregularity in the curve 
of Leptura cordifera is due to the small number of specimens 
of this species taken as it is apparent that in a small number, 
a variation of one or two individuals causes a relatively great 
irregularity in the curve. 
The curve showing the seasonal distribution of colonial 
insects such as the yellow-jackets, hornets and bumble-bees, 
is of quite a different character as will be seen by studying 
Gand H of the accompanying figure. Here the insects (fer- 
tile females) appear in small numbers with the beginning of 
the flowers in early summer. These little more than hold 
their own until the season has advanced to such a degree that 
the spirzea blossoms have about reached their maximum, when 
with the appearance of an ever-increasing number of workers, 
