5oo Gall-Gnats on Osiers and Willows, [nov., 



For a time the bark stretches, accommodating itself to the 

 thickening, so that only spindle-shaped swellings show, but 

 ultimately it ruptures and hangs down in shreds. For pupa- 

 tion the larva betakes itself to the periphery, pupation taking 

 place under only a thin epidermis, which is easily knocked 

 through by the two forehead horns of the pupa. 



Fig. I. — Cecidomyia saliciperda (magnified). After Nitsche. 



After issue of the adult gnats the bark may be seen riddled 

 with small holes. There is one generation in the year, the larvae 

 tunnelling from July till the next April, May, or June. 



Preventive and Remedial Measures. — I. Cut off and burn 

 infested shoots before issue of the adults. 



2. Cut out infested pieces and burn. 



3. Streak over with tar the places attacked, as, though the 

 pupae may occasionally push themselves through this, the flies 

 will be entangled in the sticky material. 



Cecidomyia (Rhabdophaga) salicis. 



This gall-gnat is the cause of spindle-shaped or lemon- 

 shaped galls on the one- year twigs of 5. cinerea, S. caprea 

 S. purpurea, S. aurita, and S. viminalis. 



Both leading and side shoots may be infested. The twigs 

 fail to grow, they may become angled and are rendered useless 

 for basket-making or wicker-work. 



The galls are caused by an enlargement of the pith. 



Description of Insect and Life History. — The flies — black, 

 with two stripes of white hairs — measure less than 6 mm. 

 in spread of wings. They lay their eggs in little heaps, and in 

 the multilocular gall the yellow-red larvae may be found, 

 in number up to thirty. Pupation takes place just below an 

 outside skin, which is broken through for the exit of the adult 

 gnat. The issue of the adults may take place from the end 

 of May onwards. 



