r i 6 The Scottish Naturalist. 



genus \Dineura) distinct from Nematus, with which they agree 

 in almost everything except in having two instead of one mar- 

 ginal cell in the anterior wings, while from the foregoing 

 description it is seen that the larvae are likewise similar. 



OBSERVATIONS ON THE (ECONOMY OF THE PARASITES AND 



INQU1LINES OF NEMATUS GALLICOLA AND OTHER 



GALL-MAKING SAW-FLIES. 



By P. CAMERON, Jun. 

 (First Paper.) 



'pHE insects which live at the expense of gall-making saw 

 **■ flies may be conveniently arranged under three heads. 

 i<;t, Inguilines. — These feed on the substance of the galls, not 

 on the larvae of the saw-flies, the death of which, however, is the 

 invariable consequence, and are mostly Ciirculionida and Micro- 

 Lepidoptera. 2nd, Pa?-asites. — These devour the larvae, some- 

 times as internal, but more frequently as external feeders, and 

 belong to the hymenopterous families Ichneiwwnidce and Chal- 

 cididce, as well as to the order Diptera. 3rd, Casuals.— Under 

 this may be arranged sundry insects which inhabit the galls 

 temporarily or permanently, and which are not injurious to the 

 saw-flies, or to any great extent to the galls. 



The saw-flies, especially N. gallicola, are subject to some 

 form of disease while in the cocoon. A fungus appears to 

 attack them (but it is doubtful if this is the primary cause of 

 their death), and when the cocoons are opened, especially in 

 winter and spring, they are found to contain nothing but a 

 white woolly substance. I am not here alluding to the insects 

 bred in confinement, but to those in a state of nature, and it is 

 astonishing what a number perish thus in some localities. It 

 can scarcely be caused by an excess of moisture, for the same 

 thing happens to those kept in a dry room. I have made care- 

 ful calculations regarding the mortality of N. gallicola, and, 

 taking into account those killed by disease, inquilines, parasites, 

 &c, consider that not twenty per cent, reach the perfect 

 state. Of course, some localities and seasons are more favour- 

 able for them than others. 



