INSECT PESTS OF PINE AND :SPRUCE CONES. CKLY 
If we return to the diagram fig. 42 a and draw the curve of Platygaster 
£ontorlicornis (fig. 44 a, no. 2), it is evident that the curve of this species 
shows the same relation to that of Perrisia strobi as that of MNemeritis crema- 
stloides to Laspeyresia strobilella. In the curve of Platygaster the top is cut off, 
which is brought about by the females, which in this species are far more 
numerous than the males, increasing in number to the same extent as the males 
decrease, so that the percentage of hatched insects during two days is 
the same. 
The curves, fig. 44 b, show the same relation still more plainly, the curves 
of Perrisia and of Laspeyresia being more separated one from the other. 
This close relation of the curves of Platygaster and Perrisia argues strongly 
im favour of the assumption that the former is the parasite of the latter, which 
was previously suspected, all other species of the genus Plalvgaster, the food 
habits of which were known, being parasites of gall-midges. 
An examination of material from which a great number both of Perrisia 
and of Platyvgaster had been hatched, enabled me to make certain that the 
above conclusion as to the relation of Platygaster to Perrisia was true, a dead 
Platygaster, as already earlier mentioned, being found in the inflated larval 
skin of Perrisia (fig. 27). 
There remains Zorymus azureus and Aprostocetus strobilanae, the last one of 
the more common insects hatched from the cones. As pointed out above 
the former makes its appearance only when the majority of Perrisia and La 
speyresiza have emerged, and its curve is of a quite different shape. 
While the curves of the two latter rise rapidly to 30 &, the emerging of 
the majority of them taking, as a consequence, place within a few days, the curve 
of the former hardly rises above 20 7, the emerging accordingly going on during 
a considerably longer time. In both these respects the curve of Aprostocetus 
strobilanae agrees entirely with that of Zorvmus azureus, and the diagrams no. 
4 and 5 fig. 44 a and 44 b show how closely one curve follows the 
other. From this I draw the conclusion that Aprostocetus strobilanae is the 
parasite of Zorvmus azureus, and in the foregoing paper it has been treated 
as such. 
The above conclusions are based of course not only on the diagrams now pub- 
lished but on the great material brought together during the investigations 
of the spruce-tree cone insects, which will be published later. 
This method was invented in order to enable me to ascertain the relation 
of the cone insects to one another; and its usefulness seems to be proved 
by the fact that the conclusion drawn from it regarding Perrisia and Platy- 
gaster by examination of the cones was found to be true. 
If the material could have been kept under normal conditions, the curves 
would evidently have been more separated one from another and the grouping 
of the parasites round their respective hosts still more plainly discernible; but 
it is not, at the present time, possible to make arrangements for such experi- 
ments at the Institute of Experimental Forestry. 
X. Meddel. från Statens Skogsförsöksanstalt. 
