INSECTS INJURIOUS TO ORCHARD TREES 445 



chief agencies by which scale-insects are transferred over any 

 great distances. The fact that most of them are very small 

 and inconspicuous makes it an easy matter for them to es- 

 cape detection, and thus important species are often introduced 

 into new regions even when a close watch is being kept for 

 them. For the same reason nursery stock and imported plants 

 of various kinds are the principal means of transferring these 

 pests from one country to another. 



Besides the damage that the scale-insects do by sucking the 

 juices from the plant, and, in some instances at least, poisoning 

 the tissues on which they are feeding, they may secrete a con- 

 siderable amount of honey-dew, which makes the leaves, 

 branches and fruit sticky and disagreeable to handle, and fur- 

 nishes a medium in which a black sooty fungus grows. Badly 

 infested trees present a very disgusting appearance, and the 

 fruit is often unfit for use until it is washed thoroughly to 

 remove these substances. Many insects, particularly the 

 ants, are very fond of this honey-dew and feed on it as they do 

 on the honey-dew secreted by the aphids. 



The list of scale-insects known to attack orchard trees is a 

 long one, but we shall note only a few of the most important. 



The San Jose Scale (Aspidiotus perniciosus). The San 

 Jose scale is probably the most important of 'all the scale-in- 

 sects, as it has become distributed over the whole United States 

 and is responsible for the death of many thousands of orchard 

 trees and the loss of much fruit in orchards in which the trees 

 are not killed but seriously weakened. This insect was prob- 

 ably introduced into America from China, and was first dis- 

 covered on some trees in an orchard near San Jose, California. 

 Thus it came to be popularly known as the San Jose scale. 



The covering wax scale of this insect is so small and flat 

 and so closely resembles the color of the bark, that it makes 

 the insects very difficult to detect, especially when there are 

 only a few on a tree. On the fruit or leaves or new branches 

 their presence is more easily detected on account of the con- 

 spicuous red spot that usually surrounds them. When the 

 tree is badly infested the scales often form a complete crust 

 over the bark and branches, giving them a characteristic 



