INDIRECT INJURIES CAUSED BY INSECTS. IS9 



sometimes nearly stripped by them ; so that in 1783 

 many thousand acres were on this account ploughed 

 up ^. — The caterpillar of the cabbage-butterfly {Pcipi- 

 lio Brassica, L.) is also sometimes found upon the tur- 

 nip in great numbers ; and Sir Joseph Banks informs 

 me that forty or fifty of the insects before mentioned*', 

 called by Mj-. Walford the wire-worm, have been dis- 

 covered in October just below the leaves in a single 

 bulb of this plant .^-The small knob or tubercle often 

 observable on these roots is inhabited by a^rMZ>, which, 

 from its resemblance to one found in similar knobs on 

 the roots of Sinapis arvensis, from which I have bred 

 Curculio contractus, 'Ei. B., and Rynchcenus assimilis, F., 

 is probably one of the same or an allied species'^. This, 

 however, does not seem to affect their growth. Great 

 mischief is occasionally done to the young plants by the 

 wire-worm. I last summer was shown a field in which 

 they had destroyed one-fourth of the crop, and the gen- 

 tleman who showed them to me calculated that his loss 

 by them would be lOO/. One year he sowed a field 

 thrice with turnips, whicli were twice wholly, and the 

 third time in great part, cut off by this insect. Whe- 

 ther the disease to which tui'nips are subject, in some 

 parts of the kingdom, from the form of the excrescenjces 



'Marshall in Philos. Trans. Ixxiii. 17S3, " See above, p, 168-169. 



* Swamm. ii. 81. col. b. — Gyllenhal,in describing the last-named spe- 

 ciesvso corctnon on the flowers of siliquose plants (TnsectaSuecica, iii. 142.), 

 a.iks if his R, sulcicoUis (C. Phiirostigma, E. B.), which agrees with it in 

 most respects, except in having toothed thighs, be not the other sex ? This 

 query I can solve in the negative, having taken the sexes of R. assimilis 

 in coitu, which do not differ, save that ths m^!e has a somewhat shorter 

 „rostr«m. 



