Remarks on an East Indian Turnip-fly. 301 



Perhaps a remedy may be found in pitting one insect against another, 

 the insectivorous against the herbivorous tribes ; and by encouraging, 

 rather than scaring away, the insectivorous birds. In this way the 

 larva; of the lady-bird (Coccinella) devour the "Hop-fly," (a species of 

 Aphis, and not a beetle) and save the plant : the parasitic larvse of the 

 Hymenopterce attack the insects they feed upon in all their states ; and 

 those of the Dipterce the Hymenopterous herbivorce. Of this last Mr. Yarrell 

 gives an account in the Trans. Zool. Soc. in his paper on the " Yellow fly,' 

 (Athalia centifolia) where a Dipterous parasite is described as inhabiting, 

 and having devoured the larva of that destructive insect. 



Mr. Le Keux is of opinion that the antidote against these insects 

 will be found " in some effluvia, or odour, which may be either offen- 

 sive to the insect when near, or so overpower the scent of the turnip, 

 as .to prevent the fly from distinguishing, and being attracted by it." 

 He further remarks, that so long as the plants are kept wet^the insect 

 disappears ; which agrees with my own observations on the Darjeeling 

 insect. 



The attacks of the " Turnip-fly" are said to be diverted from a plant 

 by more attractive food. Thus Mr. Le Keux has "invariably" found 

 that the white stone turnip, mixed with the Swedish turnip, protects the 

 latter ; the insects preferring the former, so that the Swedish has time 

 to grow up beyond their power of destroying it, while they are engaged 

 in devouring the other sort. This appears to be the easiest of all 

 methods of defending a crop whenever it can be done ; and well worth 

 making experiments upon. Should there be found a plant which the 

 Rungpoor insect prefers to the more precious Indigo, the advantage of 

 employing this expedient need not be dwelt upon. 



As the subject of insects hurtful to Agricultural productions is at 

 present exciting much interest in Europe, I have thought it well to 

 present the foregoing observations to the Society : for, it is of the 

 greatest consequence that attention should be every where awakened 

 to it, in the hope of discovering some remedy against their ravages. 

 It cannot be thought a trifling matter, when it is considered, that an 

 irruption of " the fly," will be as fatal to the prosperity of the planter as 

 an inundation of the Ganges. 



Journal of the Asiatic Society of Bengal for December, 1839. 



In the notice prefixed to the December number of the Journal of the 

 Asiatic Society, (which by the way appeared five months after its time), 

 we are told that the late severe Epidemic interfered so seriously with 

 the arrangements, as to render typographical mistakes unavoidable. 



