the Ravages of Slugs, Grubs, %c. 75 



numerous to be subdueth The most extraordinary circumstance is, 

 that one species of these ichneumons lays an egg.near the egg of the 

 fly. They are batched at the same time ; and it' is ascertained, that 

 the maggot from the egg of the ichneumon, either lays its egg in the 

 body of the caterpillar, when it can get at it, or devours the maggot, 

 and thus preserves the wheat from its attacks *. 



It is not here proposed, to enter into any philosophical discussion 

 regarding the origin of the wheat-fly. It is sufficient to remark, that 

 in spring, and in the beginning of summer, a species of fly is frequent- 

 ly found, in great numbers, which attaches itself to the heads of 

 wheat, when the ear begins to appear, and where it deposits its eggs, 

 which, in about ten days after they are placed in the ears, become 

 maggots or caterpillars. These destroy the young pickle, by sucking 

 up the milky juice which swells the grain, and thus, by depriving it of 

 part, and in some cases perhaps the whole of its moisture, cause it 

 to shrink up, and so to become, what in the western parts of England 

 is called pungled^. In about three weeks after, when it has exhaust- 

 ed this substance, it drops upon the ground, where it shelters itself 

 at the depth of about half an inch from the surface. There it remains 

 in a dormant state, until the mean temperature is about 58, when, 

 vivified by the warmth of spring, it becomes a fly, about the time 

 that the wheat produces the ear. 



It is evident, that the same plan, that in our climate has been found 

 so effectual for destroying the wire-worm, would be equally destruc- 

 tive to the wheat-fly, namely, that of leaving the soil which has pro- 

 duced the wheat untouched till November, and then exposing it to 

 the inclemency of the weather, and in particular to the action of frost. 



The great difficulty attending this plan is, to devise an advantage- 

 ous course of crops, consistent with the idea of putting off the plough- 

 ing of the wheat stubble till November or spring. In the celebrated 

 four years' rotation, 1. Turnips, 2. Barley, 3. Clover, 4. Wheat, the 

 wheat stubble, as a preparation for the turnip crop, might first be 

 ploughed shallow, and then a deeper furrow taken, by which the fly 

 would be buried J, scarifying and ploughing at the same time, and 

 ploughing shallow-in spring. 



I scarcely think it possible, that the fly can be destroyed, if the 

 wheat is succeeded by clover, unless, perhaps, by severe rolling and 

 treading . The minuteness of the caterpillar, which is no bigger than 

 the ordinary roman letter C, will preserve it in a great measure from 

 the effects of pressure. 



It is a great advantage attending any plan for the general destruc- 

 tion of this vermin, tlutt the young embryos are in general deposited 



* See this interesting fact explained in the Quarterly Journal of Agriculture, 

 published by the Highland Society, No. o, p. 301. 



f See Transactions of the Linnoean Society, vol. Hi. p. 302. 



j This is a plan recommended by Mr Gorrie in the Carse of Cowrie. 



An instrument, at the same time, might be invented, similar in principle to 

 the machine used at bleachfields for beating linen, which would probably de- 

 stroy the maggots of the wheat-fly in the young clover by compression.' 



