26 



The Oyster-Shell Scale 



(Lepidosaphes ulmi, L.) 



Intkoduction. — The Oyster-shell Scale is well known to nearly all the fruit- 

 growers of Ontario, as it occurs not only in every fruit district but also in most 

 orchards in these. Like the San Jose Scale, it is believed to be an imported insect. 

 When it was introduced is unknown. It has, however, been in North America for 

 more than 120 years. It is so widely distributed over the world to-day that the 

 original home is uncertain. A few years ago this insect was much feared by fruit- 

 growers, who believed it was increasing and likely to seriously injure their orchards. 

 The methods of control then advocated were thought to be unsatisfactory, and the 

 need of a simpler effective remedy was keenly felt. Fortunately this has been 

 found, and has gained the confidence of the growers. 



Plants Attacked. — Apples, pears, plums, cherries, currants and gooseberries 

 are attacked, but of these apples are much worse infested than the others. Prof. 

 Jarvis and I have found it also on rose bushes, spireas, lilacs, hawthorn, mountain 

 ash, red-osier dogwood, black ash, white ash, prickly ask, poplar (Populus tre- 

 muloides), basswood, horse chestnut and mulberry. Of these, hawthorns and red- 

 osier dogwood were the favorites, and were sometimes badly infested. There is no 

 doubt that further search would show that the insect feeds also on many other plants 

 in this Province. Prof. Quaintance, of the Bureau of Entomology, Washington, 

 D.C., in Circular 121, gives a long list of plants on which the scale has been found 

 in North America. 



Nature and Extent of the Injury. — Unlike the San Jose Scale, the Oyster- 

 shell does not attack every part of the tree, but confines itself almost entirely to the 

 trunk and branches, though occasionally it is found on the fruit of apple trees. 

 Probably the reason this is not worse attacked is that nearly all the young active 

 larvae have settled down and inserted their sucking beaks into the bark before the 

 fruit has begun to form. The new growth on the branches, except towards its 

 base, is also exempt for the same reason. The injury, as in the case of the San Jos6 

 Scale, is caused by the numerous insects with their long, hair-like beaks sucking 

 the food out of the tender tissues beneath the bark and slowly starving the trees. 

 An oblique cut beneath the affected bark shows little brown areas where the scales 

 have fed. In my experience the insect exhibits a decided preference for neglected 

 and weakened trees, such as those we see along the roadside or in fence comers 

 here and there over the farm, or in orchards that have been starved or weakened by 

 winter injury. It is not at all uncommon to find the above classes of trees so badly 

 attacked that the bark is almost concealed by the scales. Young trees as a rule 

 seem to be worst infested. Occasionally a tree badly attacked dies, but usually 

 they continue to live for many years in a weakened condition. The bark on these 

 trees becomes after a few years very rough and scurvy, and even if the scale is 

 killed does not recover its smoothness for several years. In thrifty orchards the 

 insect is seldom very abundant, though it is usually present in moderate numbers 

 in most of the -trees unless they have been treated to destroy it. Occasional 

 branches in these orchards may be so badly attacked as to die, but this is not very 

 common. 



