THE PHYTOMYZA LEAF TUNNELLER. 71 



CHAPTER LI. 



THE PHYTOMYZA LEAF TUNNELLER. 



(^Phytomyza affinis.) 



Order : Diptera. Family : Muscidoe. 



An almost black minute two-winged fly (see Fig. IIa.), 

 which does immense damage to vegetation, especially if of 

 a succulent nature, by tunnelling or blistering the under- 

 side of the leaves of many plants as cabbage, turnips, 

 cinerarias, and a host of other plants, especially those 

 belonging to the Order Compositse, many of which, as 

 milk thistles (^Sonchus)^ being veritable breeding grounds 

 for swarms of this pest. The eggs are deposited on the 

 leaves of the plant, and when hatched at once commence 

 to make irregular galleries into the leaves, the larvas, also 

 the pupae, being safely concealed under a kind of film or 

 web, and from which the perfect insect may easily be reared 

 by any one desirous of trying the experiment. In our 

 plate is shown the blister-like tunnels on the underside of 

 the leaf, also the larvae and pupa3 in their natural sizes, 

 and on Fig. V. a section of the " blister " laid open, and 

 showing a larva enclosed therein. Fig. II. shows the 

 perfect insect, highly magnified, and in various positions. 

 Figs. VI. and VJa. represent a singular Hymenopterous 

 (four-winged) fly, which works great havoc on this pest 

 when in the larval and pupae state, the specimens from 

 which the illustrations have been taken having been 

 reared from lettuce leaves gathered for the occasion. 



