29 
Mr. Henry Le Keux on the Turnip Fly. 
where the fly was particularly numerous, I marked out a small 
square, and with a syringe washed over every plant within it, singly, 
with sulphate of potash ; but although it was so strong as to destroy 
some of the plants, and to leave a white sediment when dry upon 
all, I found the flies upon them the next day nearly as numerous as 
before this application. I wetted some of the plants with distilled 
water, (spring-water does not adhere so well to the plant,) and 
these were entirely free from the fly so long as they remained met ; 
and if one happened to alight upon a wet plant, it instantly sprang 
off again. But of all the numerous applications which I tried upon 
the leaf, none were effectual in deterring the fly, though detrimental 
to the plant itself; and I found any attempts of this kind must be 
unavailing, because although the upper side of the leaf may by 
any preparation be rendered unpalatable, and even poisonous, to 
the insect, it will still eat away the underside with impunity, and 
leave nothing but the upper epidermis or skin. 
I next tried various matters mixed up with or strewed upon the 
earth, that might be offensive to the fly by the odour or effluvia ex- 
haling from them. The first of these was powdered sulphur strewed 
over about one-tenth of an inch thick ; the effluvia from this was 
perceptible to me when standing near it if the sun was shining, but 
so far from deterring the flies, I thought they appeared more nu- 
merous in this spot, and it certainly improved the appearance of 
the plants growing in it. 
Amongst many other things, I tried snuff and assafoetida, and a 
box of the powder for preserving furs from moth, sold under the 
title of “ Anti Tinea," but none of them had the slightest effect. 
Latterly I found it more convenient to try the effect of various 
substances on the side of a cage containing a great number of the 
flies, and having placed a small piece of carbonate of ammonia there, 
to my great delight all the flies drew away from it and kept in the 
further side of the cage ; upon changing its position to the side 
where they had all congregated, they immediately began to move 
away again. I then took a glass tube containing a number of 
them, and placing the lower gauze wire upon a large piece so that 
the effluvia from it might pass through the tube, when they in- 
stantly began to leap violently, but in a few seconds fell to the 
bottom motionless ; I immediately removed them, but they were 
quite dead, for not one recovered though laid upon fresh leaves. 
I congratulated myself on having at last found the object of my 
search, and went the same evening up the hill and sowed a patch 
with turnip seed, and on the fourth day (which I waited for with 
impatience) when I expected the plants to appear, I strewed it over 
