Watt. — Leaf-mining Insects of New Zealand. 209 



midrib of the leaf, usually an effectual barrier except in its upper sixth. 

 Occasionally in large leaves the course of the gallery will be but little 

 deflected. The gallery may average 6 in. in total length. I have found 

 that the Wellington mines are as a general rule much larger and less 

 tortuous than the Egmont ones, which are frequently so tortuous as to 

 be almost confined to about a square inch of the leaf-surface exclusive of 

 the blotch ; in such cases the leaf-substance between the convolutions 

 of the gallery soon becomes dead and of the same colour as the gallery, 

 and so simulates a blotch which may be separate from or coextensive with 

 the actual blotch. The blotch is irregular in shape, its margin fairly even, 

 and may average f square inch in area ; its construction occupies about 

 a week. 



Frass is plentiful, finely granular, black, and in the gallery is deposited 

 in the central three-fourths of the mine ; a tendency is sometimes seen 

 for the frass to be deposited in a double row, but this is infrequent and 

 generally not very marked. In the blotch the frass is found chiefly in 

 the earlier portion, and is arranged in rows or shallow loops, convex for- 

 wards, across the mine in the track taken by the larva. The last act of 

 the larva is to prepare an outlet at the margin of the blotch, and just 

 within this it constructs its cocoon. 



The early part of the gallery frequently follows the midrib, margin, or 

 one of the coarser veins of the leaf, but these latter do not form very 

 serious barriers to the young larvae. The width of the gallery, though 

 irregular, increases gradually till it suddenly expands into the blotch. The 

 average width would be about 1 mm. The blotch is frequently against 

 the margin of the leaf, and always includes a small portion, \ in. or so, 

 of the terminal portion of the gallery. The midrib and veins are more 

 effectual barriers to the blotch than they are to the gallery. Colour of the 

 mine in the freshest portion pale green, but the cuticle rapidly becomes 

 dead and brown over the roof of the mine. Frequently irregular portions 

 of the gallery become reddish-brown, but the darkest discoloration is in the 

 immediate neighbourhood of the ovum and the first 1 mm. or 2 mm. of 

 the mine. The blotch becomes brown very rapidly, even while the larva 

 is at work. The mine becomes very conspicuous in consequence of these 

 colour-changes. In the blotch, before the cuticle dies, the frass rows are 

 clearly discernible. The frass is deposited against the upper cuticle, to 

 which it adheres ; sometimes in the gallery it may occupy a narrow, more 

 or less uninterrupted central line. 



On the underside of the leaf the mine can hardly be seen, its presence 

 being sometimes made known by a slight swelling of the under-surface 

 along its course. Beneath the blotch, however, the under-cuticle becomes 

 loose and wrinkled, and loses its slightly roughened appearance. 



The Larva. 



When young the larva is white in colour, flattened, moniliform; 

 alimentary canal greyish-brown. In the fully-fed larva the body is cylin- 

 drical, only very slightly flattened dorso-ventrally ; length about 5 mm. ; 

 head flattened, retractile, rounded, in the younger larvae bluntly triangular ; 

 segments well rounded but not deeply incised, the mesothorax has the 

 greatest diameter, the metathorax and first seven abdominal segments being 

 about equal, segments 8 to 10 acutely attenuated ; there is a deep constric- 

 tion between 8 and 9 ; 9 is very small. Ground-colour palest green, almost 

 white ; central marking fairly broad, light yellow from the head to the 



