CXLIV I. TRÄGÅRDH. 
each breeding-case and, based on the number of each species which emerged 
day after day, to draw diagrams. 
I took as my basis the supposition that a certain relation existed between 
the time of emergence of the host and its parasite; the latter being adapted 
both morphologically and biologically for its host and appearing invariably at 
the moment most suitable for its successful propagation. This relation might, 
of course, be different according to the instar of the host which were attacked 
by the parasite. 
It is true that the insects were not subjected to natural conditions in the 
breeding cases, their development being in them doubtless much accelerated. 
But, on the other hand, one might safely presume that these conditions did not alter 
the relation between the time of emergence of the host insect and its para- 
sites. 
Further there existed certain known data as to the relation of Nemeritis 
cremastoides HGN, Ephialtes glabratus RATz. and Bracon sp. to Laspevresia strobi- 
Zella IT. If other parasitic species grouped themselves around one or the 
other of the phytophagous species, it might safely be concluded that they 
were the parasites of these. 
The success of this method, however, depended on the phytophagous spe 
cies not appearing contemporaneously but in a certain succession. Fortunately 
the latter was the case. Figs. 42 a and b are diagrams showing the number 
of Perrisia strobi (no. 1), Laspevresia strobilella (no. 2) and Zorvmus azureus (no. 
3), calculated in percentages of the total number of each species, hatched 
from two different localities. 
We notice in fig. 42 a that the gall-midges start emerging on the 17th of 
April and increase rapidly in number so that on the r9th 30 percent emerges; 
on the 2oth the number decreases, on account of the number of males rapidly 
diminishing before the females have reached their maximum. On the 22nd 
also 30 2; emerges, the number subsequently quickly decreasing. 
Three days after the gall-midges the cone-moths make their appearance, 
their number increasing rapidly, attaining two days afterwards its maximum 
with 28 2; and subsequently quickly diminishing. Not before the cone-moth 
has nearly ceased emerging does Zorymus azureus begin to appear, and the 
curve of the latter rises and goes down much more slowly than that of 
the two other species. 
The diagram fig. 42 b shows the same succession of the three species and 
almost the same shape of the curves as in fig. 42 a. 
Consequently there exists the difference in the time of appearing of the 
phytophagous insects necessary to enable us to ascertain how the parasites 
group themselves round their hosts. 
'The diagram fig. 43 shows the curves of Perrisia strobi (no. 1), Laspevresia 
strobilella (no. 2) and its parasite Nemeritis cremastoides (no. 3). We notice 
that the latter appears three days after its host and ceases emerging one day 
after the latter. Both curves have two apices, on account of the number 
of the males, which invariably make their appearance a couple of days earlier 
than the females, decreasing more rapidly than the number of females increase. 
The difference between the apices of the host and the parasite is only one day. 
This diagram shows, as a consequence, that the curve of the parasite closely 
follows that of the host, with an interval of one or two days. 
