THE MANGOLD -FLY. 11 



laid together we should expect to find eleven larvffi in a leaf; 

 from what we know of the gastronomic powers of a single larva, 

 where this happens the struggle for existence must eventually 

 be rather severe. Farsky gives the result of an experiment on 

 the extent of leaf blotched by eleven larvse transferred from 

 affected leaves to a fresh one. In six hours the blotch measured 

 twelve square centimetres, and in twenty-four hours fifty-eight 

 square centimetres, but as in all insects the amount of food con- 

 sumed in a given time varies greatly according to many circum- 

 stances. 



The full-fed larva is about one third of an inch (7—9 mm.) 

 long. It is apod, conico-cylindrical in shape, wide at its anal 

 extremity, and tapering gradually from the 7th segment to the 

 head; this carries two black retractile hooks. Westwood says 

 " the mouth of the larvae of the genus Pegomyia is furnished with 

 a corneous instrument in the shape of S, which moves round a 

 small fixed point, enabling them to scrape up the soft parenchyma 

 of the leaf." In colour it is pale yellowish white, showing greener 

 towards its thickened extremity from the intestines showing 

 through. This led Mr. Graham to describe the larva as greenish ; 

 its frass is dark green. A pair of stigmata are placed just before 

 the second segment; Farsky shows them greatly magnified in 

 his figure, which is here copied, and 

 says they resemble a seven-rayed fan 

 (magnified, st). He also figures and 

 minutely describes the truncate terminal 

 segment (magnified, a.s) ; on the dorsal 

 sloping part are four twin, fleshy appendages ; in the centre below 

 these are two papillte, with two more spiracles ; there are two very 

 inconspicuous protuberances on the ventral surface. It is there- 

 fore an amphipneustic larva, according to Haliday's classification. 

 When full-fed the larva generally eats its way out of the leaf, and 

 pupates in the ground, but occasionally this takes place within the 

 leaf, as did the specimens described by Curtis. Mr. F. Norgate says 

 he finds the pupae about three inches below the surface, and again, 

 *' I cannot find a single pupa in the leaves, nor have I induced a 

 larva to pupate in a leaf, but believe this always takes place under- 

 ground." It migbt be thought that Curtis refers to a distinct 

 species, but Farsky specially tells us that from his experi- 

 mental leaf some pupated underground, while others did 



