THE 



GARDENER'S MAGAZINE, 



NOVEMBER, 1837. 



ORIGINAL COMMUNICATIONS. 



Art. I. A Series of Articles on the Insects most injurious to Cultiva^ 

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

 Society of London. 



No. 9. The slimy Grub of the Pear and other Fruit Trees. 



In my last article, I gave the history of an insect which, in the 

 larva state, feeds upon the leaves of the apple, devouring the 

 entire leaf. On the present occasion, I have to describe the pro- 

 ceedings of another leaf-feeder ; but in this case the insect ex- 

 hibits the singular instinct of eating only the upper surface of 

 the leaf, leaving the under parenchyma with all the fibres and 

 veins untouched. Such is the habit of the larvae of several 

 species of saw-flies, composing Professor Hartig's subgenus 

 Blennocampa, and which has obtained this name in reference to 

 the unsightly appearance of the larvae, which are ordinarily- 

 covered with a slimy secretion, giving them a resemblance to 

 minute black slugs. In America, indeed, the name of slug- 

 worm is given to one of these insects inhabiting that part of the 

 world, and which, towards the close of the last century, became 

 so prevalent as to threaten the destruction of the cherry, pear, 

 quince, and plum ; all of which trees were infested with it : the 

 small trees being covered with insects, and a breeze of air through 

 those on which they abounded becoming charged with a very 

 disagreeable and sickening odour. Twenty or thirty were to be 

 seen on a single leaf; and many trees, being quite stripped, were 

 obliged to put forth fresh foliage, thus anticipating the supply 

 of the succeeding year, and cutting off the prospect of fruit. 

 {W. D. Peck, Natural History of the Slug-Worm. Boston, 

 1799.) 



The peculiar odour mentioned above was evidently emitted 

 by the slimy secretion with which the insect clothed itself, and 

 which might be supposed to have the effect of repelling the 

 attacks of parasites. Professor Peck, however, has figured a 

 small hymenopterous parasite, apparently belonging to the 

 genus Encyrtus (fam. Chalcididae), peculiar to it. 



Vol. XIII — No. 92. i i 



