THE CANADIAN ENTOMOLOGIST 



ventrally to such an extent that its anterior margin has a chisel-Hke edge, from 

 which project a pair of sharp mandibles. (Fig. 4.) 



The young hirva is very deHcate, but it begins at once to enlarge the cavity 

 in which it hatched, feeding only on the palisade cells of the leaf just under the 

 upper epidermis Throughout its life the larva feeds on these cells only and 

 ne\er attacks the lower layer of cells forming the spongy tissues of the leaf. 

 These latter turn black about 24 hours after the overlying layer of palisade 

 cells have been eaten, and this black colour showing through the transparent 

 upper epidermis causes the unsightly disfigurement of attacked leaves, as shown 

 in Fig. 1, B. 



The larva is unable at first to eat through the larger veinlets, but the eggs 

 are always laid within half an inch of the leaf margin, where the veins are very 

 fine, thus assuring an ample food supply before the larva is strong enough to 

 tackle the larger veins, the mid- rib of which will in time be eaten through. 

 Often several eggs are laid in one leaf, in one case as many as 13 were counted, 

 but a large percentage fail to hatch. The larvae are by no means gregarious. 







Fig. 2. Old feeding punctures on under side of leaf showing ". J 

 corky tissues developed around punctured area. 



Fig. 3. Adult of Z. sculellaris, x 7. 



When the burrows of two larvse of approximately equal size join up, these 

 two larvse may both live if they remain in different areas of the single blister 

 thus formed, but in nearly every caseonly one survives A large blister covering 

 almost an entire leaf frequently contains one healthy larva only, together with 

 six or seven smaller dead specimens which show no apparent cause for death. 



The larvae are found with the ventral side uppermost. They are legless, 

 and can move as readily on the dorsum as on the venter. While in the blister 

 they are very active and can move rapidly, but when removed from it their 

 progress is very slow 



In figure 4 we illustrate a larva of this species in the penultimate stage. 

 The characteristic black markings on the meso- and meta- thoracic and on 

 the abdominal segments are present in all stages of this larva, with the exception 

 of the first and the final stages. They occur both on the dorsum and venter. 



By the middle of September the majority of larvae are mature, measuring 

 6 mm long. They now break through the thin upper epidermis of the leaf 

 (Fig 1 C) and fall to the ground. 



In captivity the escaped larva burrows into the soil to the depth of about 4 



