284 Transactions. 



membrane of the food plant the posterior processes (Plate III, fig. 5) 

 are extruded through the cuticle of the leaf, while the anterior pair, 

 situated as they are toward the ventral line, are embedded in the tissues 

 of the leaf. When viewed laterally under the microscope an anterior 

 process (fig. 16) is seen to consist of a dome-shaped body terminating 

 in a black knob-like head, the lower margin of which is drawn out to a 

 point. Immediately above the anterior process is a pair of contiguous 

 lobes distinguished by a central fissure. Each posterior process consists 

 of a light-brown stalk terminating in a rounded dark-brown head. The 

 pupa, when at rest beneath the leaf- membrane, is easily seen with the 

 unaided eye, but under the microscope presents a unique appearance, due 

 to the cellular structure of the leaf (Plate III, fig. 3). A photograph of 

 the exposed pupa is shown in Plate III, fig. 4. Length of pupa, 2 mm. 



Two minute hymenopterous parasites attack this fly, and are very 

 common. They belong to the Ghrysocharis sp., but neither are as yet 

 further identified. The larger of the two was seen ovipositing in a newly 

 hatched larva of P. albiceps. the membrane of the leaf evidently being 

 pierced in the process. Apparently the larva of this parasite lives in the 

 larva and pupa of its host, for specimens were always obtained from 

 infected pupae of the fly. One can tell at a glance whether a pupa is 

 infected or not, since those containing parasites are black and opaque, and 

 are a great contrast to the rich brown and semi-transparent pupae of 

 healthy flies. It appears that not more than one Hymenopteron is reared 

 from any one host. 



The smaller of the two parasites has now several times been seen 

 ovipositing in the pupae of P. albiceps, often walking over and com- 

 pletely ignoring living larvae. As such pupae were in each case observed 

 infested with the larger parasite, it may be quite possible that this smaller 

 species is in reality a true hyperparasite. A full account of the lives, habits, 

 and life-histories of these two Hymenoptera will form the subject of some 

 future contribution. 



Food Plants oj Phytomyza albiceps. 



The common sow-thistle (Sonchus as per) is the favourite food plant. 

 Also found plentifully on S. oh raceus, and S. arvensis. Has been found 

 burrowing in dahlia, dandelion (Taraxacum officinale var. glabratus (?) ), 

 large nettle (Urtica ferox), Cape-weed (Cryptostemma calendulacea), common 

 groundsel (Senecio vulgaris). 



Rah. — -Wanganui. October to April (M. N. W.). ; Whakamaiina. Decem- 

 ber (D. M.). 



EXPLANATION OF PLATES. 



Plate II. — Phytomyza albiceps Mg. 



Showing egg-pocket and track of mine made by the larva during the nine days of 

 its larval period. (Note the progress during the last three days.) 



Plate III. — Phytomyza albiceps Mg. 



Fig. 1. Egg-pocket in leaf. The egg is visible under the thin cuticle of the leaf. 



(Note the empty pocket above.) x 18. 

 Fig. 2. Larva, full-grown, uncovered. X 14. 

 Fig. 3. Pupa beneath cuticle of leaf. X 14. 

 Fig. 4. Pupa exposed (lateral view). X 14. 

 Fig. 5. Posterior respiratory processes of pupa pushed through the cuticle of the 



leaf, x 56. 

 Fig. 6. Phytomyza albiceps. Photographed from life, x 2. 



