An introductory lecture delivered on the opening of the session of the Medical School, Charing Cross Hospital, London, October 1, 1852 / by Edward Smith.

  • Edward Smith
Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: An introductory lecture delivered on the opening of the session of the Medical School, Charing Cross Hospital, London, October 1, 1852 / by Edward Smith. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    freed from their great destroyer the lio])-fly {Aphis HiumiH)—not from the efforts of the hop-growers, who considering it a blight brought by some cold wind or atmospheric change, fold their arms in helpless apathy ; but in conseqiience of the investigations into the history and economy of the insect by an eminent British entomolo- gist, Mr. Francis Walker*, who has attended very closely to this tribe. The difficidty in the case of the hop-aphis has always been to know where the eggs from which the flies proceed in spring, are placed by the gravid females in autumn. This could not be on the hop-plant, which dies down yearly to the roots. But the mystery has been solved by Mr. Walker, who has found that it is on the sloe-ti-ee or black-thnrn (Prunns sjnnosa) that the female deposits her eggs in autumn, which are there hatched in spring, and the second generation being produced with wings, flies to the hop- plants and establishes itself on the leaves, which, owing to the well- known ra])id increase of these insects, it soon covers and exhausts of the sap. Now if the hop-aphis does not deposit its eggs on any other shrub or plant than the sloe, as Mr. Walker believes, it is evident that, to secure the ho])s in any district from the hop-aphis, it is only necessary to destroy all the sloe-trees, which, as they are found chiefly in hedges, and there in no great number, wonld be no difficult matter. And if, from the escape of a part of the sloe-trees, and the flight of some of the hop-aphides from distant quarters, a few of the female aphides were still found on the hop-plants in spring, nothing would be easier, as I ascertained by experiments in hop- grounds in Worcestershire in 1838f, than to clear them from every one of these assailants, at a very trifling expense, by employing women and children, by means of step-ladders, to crush every aphis found, by pressing them and the leaf between the thumb and fore- finger, so as to destroy the flies without injuring the texture of the leaf. When it is considered that the extirpation of the hop-aphis would in some years save 20G,000Z. to the revenue, and three or four times as much to the hop-growers, it is evident that this is a matter worth attention, and that the science which can eff'ect this saving is no trifling one. Let it be one of your main objects, Gentlemen, by sedulously cultivating this department of your pur- suit, to prove that it is not so, but, on the contrary, one of those which may exert the most striking influence on the j)rosperity of mankind. * Annals of Nat. Hist. 1848, voL i. p. 37.3. t Introd. to Ent., 6th edit., vol. i. p. 149. Printed by R. and J. E. Taylou, Red Lion Court, Fleet Street.
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