GALLS CAUSED BY FLIES 73 



pea-like form on the aerial roots of various species of Cattkya, 

 doing much damage; and Cecidomyia rhododendri causes 

 bud-like growths on the twigs of various species of Rhodo- 

 dendron. 



The Cabbage - root fly, Phorbia brassicae, is not only a 

 Cabbage pest, but often does considerable mischief in turnip 

 plots, causing swellings which resemble somewhat those of 

 the Turnip gall weevil. Full particulars concerning its 

 life-history, etc., are given in Theobald's second report, 

 "Economic Zoology," p. 68. It also attacks the Shep- 

 herd's Purse, Charlock, Jack-by-the-Hedge, Wall Mustard, 

 and the Stock, but I am not aware that it causes galls to 

 arise on these plants. 



Certain members of the genus Diplosis are well-known 

 pests. D.flava and D. tritici attack wheat ; the larvae of the 

 former give rise to rosettes of leaves on the haulm ; those of 

 the latter induce swelling of the glumes and flowers. Diplosis 

 pyrivora, the Pear Midge, not infrequently causes serious 

 losses in Pear orchards. It attacks the blossoms, and de- 

 posits its eggs with the long egg-laying tube. The eggs 

 hatch in from four to six days. About a fortnight later the 

 fruit begins to swell abnormally, and is gradually hollowed 

 out by the larvae, which, in common with other members of 

 the genus, have the power of leaping. (See Board of Agri- 

 culture leaflet, No. 53.) 



The " Ribbon-footed corn-fly," Chlotops iaeniopus Miegen, 

 causes the malformation known as " gout " in the haulm of 

 Wheat, Rye, and Barley, most frequently on Barley. " The 

 attack takes its common name of ' gout ' from the swollen 

 state of the heads when the ear is unable to burst the 

 sheaths. Whilst the plant is still young, and the forming 

 ear is wrapped in the sheathing leaves, the fly places her 

 eggs either within these leaves or so that the maggot can 

 make its way through them to the ear; there it usually 

 eats away some parts of the lowel^ortion of the ear, and 

 then gnaws, or rather tears, a channel down one side of the 

 stem to the uppermost knot, and beneath the leaves th.& 



