THE CANADIAN ENTOMOLOGIST, 237 



at work on the plants, if the earth is scraped away from about the stem of 

 each and a handful of lime dusted around it and the soil again drawn up 

 to the stem, the plants will sometimes recover. Coal-dust, gas-lime and 

 stimulating artificial manures have also been recommended. 



The cabbage has also suffered from injuries caused by the common 

 cabbage worm, the green caterpillar of the cabbage butterfly which feeds 

 upon the foliage, and often disfigures it to such an extent as to render it 

 unmarketable. The habit of this caterpillar, feeding as it does among the 

 folds of the leaves, makes it extremely difficult to reach with any sort of 

 poison without at the same time rendering the cabbage unfit for use. 

 Pyrethrum or insect powder, which is the powdered flowers of Pyrethrum 

 cinncrariae/oliu/n, has been used with good effect, either dusted on the 

 plants, or mixed with water and applied to them with a syringe, and this 

 remedy is not in any way objectionable or poisonous. The Pyrethrum 

 plant is in my experience quite hardy in Ontario, has stood the severe 

 cold of the past two winters without injury, and flowered freely. It is 

 easily raised from seed, and being a perennial species, when once estab- 

 lished it will continue to flower for an indefinite number of years. The 

 flowers, collected when just about to expand, dried and powdered, are 

 very efficient as a general insecticide. 



During the past year or two many interesting experiments have been 

 made and valuable results obtained, in the way of artificially introducing 

 disease among communities of caterpillars, a sort of caterpillar plague 

 or pestilence which carries them off by thousands. There is a very fatal 

 disease which appears from time to time among silk worms, the 'larvse of 

 Bombyx inori when bred for the production of silk, a disease which spreads 

 so rapidly that it frequently destroys entire broods of caterpillars within a 

 few days. So destructive has it been that it is estimated that the silk crop 

 in Europe is damaged by it to the extent of many millions of dollars an- 

 nually. During the past ten years it is believed to have reduced the in- 

 come of silk breeders some twenty-five per cent, and in 1879 was said to 

 be the main cause in the great falling off in the silk crop of that year, 

 which was only about one-fourth of the amount ordinarily produced. The 

 celebrated Pasteur investigated this disease, and found it to proceed 

 from the presence of an exceedingly minute form of bacteria, so excessively 

 small that it has been estimated that it would require eight millions of 

 them to cover the head of an ordinary pin. When water containing these 

 minute organisms is sprinkled on the leaves on which the silk worms are 



