166 TREE WOUNDS AND DISEASES 



these insect pests. The following formula is 

 highly recommended in the case of aphides 

 generally, but the rose aphis in particular : 

 Nicotine sulphate, ^ oz. ; whale oil soap, 

 -J Ib. ; water, 5 gallons. 



The Oyster-shell Bark Scale (Aspidiotus ostrce- 

 formis). This scale insect attacks most of our 

 fruit trees, including the apple, pear, plum, 

 and cherry. It may readily be detected by 

 the shield or covering, which bears a resem- 

 blance in miniature to an oyster shell, being 

 only about one-twelfth of an inch in diameter. 

 Usually occurring in large numbers on the 

 bark of infested trees and living on the sap, 

 the health of the specimen soon gives way, and 

 in cases where the attack was aggravated we 

 have known the tree to be killed outright 

 during the third year. Fortunately, this scale 

 insect may be kept in check by timely appli- 

 cations of paraffin emulsion to the bark of 

 infested trees. 



The Mussel Scale (Mytilaspis pomorum). 

 Amongst scale insects this is one of the most 

 troublesome, not only in the case of fruit 

 trees, but several species of thorn and allied 



