CONTRIBUTIONS FROM THE WISLEY LABORATORY. 269 



CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



XXIII.— A TRAP FOR TURNIP-FLY. 



By Prof. H. M. Lefroy, M.A., F.Z.S., Entomologist. 



The Turnip-Fly or Turnip-Flea Beetle is a well-known pest of turnips, 

 swedes, cabbages, and allied cruciferous plants in the seedling stage. 

 I The commonest form is a minute bluish beetle, which in fine sunny 

 f weather is seen sitting on the little seedling plants, and which eats 

 ! small round holes in the leaves. The beetles attack plants in all 

 I stages, and may be found eating holes in the leaves of the full-grown 

 I plants, but their destructive power is mainly exercised on the first 

 ' two leaves of the plants as they come out of the ground, or on the 

 first rough leaves which follow them. At this stage the plant is 

 wholly dependent on its leaves, any injury to which results in a 

 serious set-back to its growth. Later on the injury these small 

 beetles cause is of much less importance, as the large leaf surface 

 is sufficient for the plant, and the small holes made by the beetles do 

 not reduce the leaf-area greatly. 



At Wisley, as elsewhere, turnips were sown in August with a view 

 to the winter food supply, and the seedlings were heavily attacked, 

 mainly by the blue flea-beetle [Phyllotreta consohrina), and also, but to a 

 lesser degree, by the yellow-striped form (P. undulata). The seed was 

 drilled in rows a foot apart, and the young plants became infested from 

 a neighbouring plot of broccoli. It was observed that, when the 

 flea-beetles were disturbed they leapt outward from the plants, 

 ahghting about midway between the rows. It seemed clear that, if, 

 instead of the soil, one could place a sticky layer for the beetles 

 to alight on, many would be caught. Acting on this idea, the trap 

 now to be described was devised. 



A rough pattern was made, coated with vasehne, and tested on 

 three rows of the plot. Two days elapsed and these three rows made 

 such extraordinary growth, as compared with the rest of the plot, that 

 further trials were made. It was evident that the beetles were being 

 caught, as they were there in the vaseline in scores, but the results 

 were more striking than had been expected. 



As a result of further trials the following seems to be the best 

 pattern of trap : — 



The trap consists of two boards set at a slope on a pair of runners, 

 like those of a sledge or toboggan, with a space between. The trap 

 is drawn along the drill, so that the plants pass down the space in the 

 middle. In order to disturb the beetles, a loop of string hangs from a 

 cross-bar and brushes the plants. 



Disturbed thus, the flea-beetles leap away sideways, alight on 



