INSECTICIDES ON GARDEN AND GKEENHOUSE PESTS. 749 



necessary to repeat the application. Keep the plants well in the 

 shade for a week or more after spraying. I have not found the 

 carbon bisulphide injurious to Maidenhair Ferns while in active 

 growth, but in no case must the plants be exposed to the sun. 



The Peak-tree Saw-fly, or Slugworm 

 (Selcuidria atra). 



Although this insect is not so universally destructive as many of our 

 fruit pests, it is decidedly one of the most injurious to wall-trained fruit- 

 trees, and when once established is very persistent in its attacks, often 

 destroying successions of crops year by year as the seasons come. 



My experiments with this pest began in the year 1899, upon a series 

 of wall-trained Pears and Cherries, the nature of the infestation being 



Fig. 315. — Pear-teee partly Defoliated by Slugworms, July 1899. 



one of the worst I have ever seen (fig. 315), and one, I am informed, of 

 very long standing. 



It is when the leaves are well formed in the spring that the parent fly 

 appears and lays its eggs. This is accomplished in a rather interesting 

 way. The female fixes herself to the underside of a leaf and with her 

 ovipositor makes a slit through the leaf to the upper surface, leaving the 

 bare epidermal layer intact. The egg is placed immediately beneath the 

 latter, and is clearly visible to the naked eye as a sub-circular spot, varying 

 in colour according to the age of the egg. The latter is of a pale leaf- 

 green, sub-circular, flat beneath, and low convex above. In the course of 

 a few days the young larva hatches from the egg, cutting its way through 

 the shell and epidermis of the lea? much in the same way as a moth 

 larva. All through its existence the larva feeds upon the upper surface 

 of the leaf, leaving the nervures untouched as a skeleton network, with the 



