Insects most injurious to Cultivators. 103 



seems at first to be turpentine. The latter custom, in this warm 

 climate, is a very good means of promoting digestion. 



This is nearly the amount of the notes which I wrote during 

 my stay in this country. I can, if you wish it, communicate 

 other matters to you, perhaps still more agreeable than these. 



Soho, London, September, 1838. 



Art. II. A Series of Articles on the Insects most injurious to Cultivators. 

 By J. O. Westwood, F.L.S., Secretary to the Entomological So- 

 ciety of London. 



No. 15. Celery and Chrysanthemum Leaf-Miners. 



The leaves of plants have been with great propriety termed 

 their " lungs," since, being the principal organs of inspiration, 

 and contributing to the growth of plants by their powers of 

 absorption, it necessarily follows, that the health and vigour of 

 every plant depend very much on the number and amplitude 

 of the leaves. Defoliation, either naturally or by art or acci- 

 dent, instantly arrests their growth, and the failure or diminished 

 expansion of foliage is a " certain sign of debility." {J. Main 

 in Brit. Cyclop. Nat. Hist. vol. i. p. 580.) In the higher ani- 

 mals and man, we know, by sad and numberless instances, that 

 derangement, even be it ever so slight, in the respiratory or- 

 gans, produces immediate and baneful results upon the system. 

 And we may readily conceive, that when the entire substance of 

 a leaf has been eaten by a caterpillar, or its parenchyma de- 

 voured by a minute larva, which has the instinct to leave the 

 two surfaces of the leaf entire, the effect is the same ; inspiration 

 and respiration are prevented, and the plant gradually sickens, 

 unless, indeed, it has power to throw out fresh leaves. 



The mining of leaves by caterpillars must have attracted the at- 

 tention of many of our readers, who may have noticed on the leaves 

 of many plants, as the rose, sweet briar, bramble, primrose, al- 

 der, vine, &c, various slender tortuous lines gradually becoming 

 wider, running in all directions, distinguished by their brown 

 withered colour. These, to the incurious observer, appear to 

 be nothing more than withered parts of the leaf, produced by 

 some atmospheric action, which he terms blight. They are, 

 however, the tracks of minute caterpillars which reside within 

 the leaf, and which feed upon the parenchyma, often under- 

 going their transformation to pupae within the leaf, out of which 

 they protrude themselves previously to assuming the perfect state, 

 by the assistance of the short spines on the dorsal segments of 

 the abdomen, as in the case of the rose moths, described in a 

 previous article. In other species, the larvae, when full-fed, 

 quit the leaf, and descend into the earth, where they become 



h 4 



