THE 



GARDENERS MAGAZINE, 



MAY, 1837. 



ORIGINAL COMMUNICATIONS. 



Art. I. A Series of Articles on the hisects most injurious to Cul- 

 tivators. By J. O. Westwood, F.L.S., Secretary to the Entomo- 

 logical Society of London. 



No. 3. The Turnip Saw-Fly. 



One of your correspondents (J. B. W., Vol. XII. p. TIL) having 

 recently enquired for an account of the economy of " the small 

 black grub which lately made such havock amongst the turnips," 

 and the same insect having been selected by the Council of the 

 Entomological Society as the subject of the Prize Essay for the 

 year 1837, I have determined on making this destructive insect 

 the subject of the present article; not only with a view of detail- 

 ing what is already known concerning it, but also for the purpose 

 of noticing several particulars relative to its economy which it is 

 desirable should be ascertained. 



About the year 1760, and again in 1782, as we learn from a 

 paper by Mr. Marshall, published in the Tranmctions of the 

 Royal Society for 1783, many thousands of acres of turnips, in 

 certain parts of the country, were entirely destroyed by this insect. 

 In 1818, it again appeared in great numbers, and to a still greater 

 extent in 1835 and 1 836. The destruction is produced by the vora- 

 cious larva, or grub, of this insect, which, from its colour, is called 

 the nigger, or black grub ; and a field of turnips infested with it 

 is said to have the "blacks." These larvae {fg. 73. a, i)are of a 

 cylindrical form, and of a slaty or greenish black colour ; having 

 a darker-coloured line down the back, and a longitudinal pale 

 grey or dull yellowish line, succeeded by a dark slate line ; the 

 under side of the body being also pale-coloured. The body is 

 transversely wrinkled, independently of the articulations. The 

 head is black, armed with the ordinary apparatus of a masti- 

 cating insect ; namely, an upper and under lip, two horny jaws, 

 and two coriaceous under jaws, acting transversely. The three 

 Vol. XIII. — No. 86. o 



