113 



species, however, the young- are broug^ht forth alive in the San 

 Jose scale almost always, and at least occasionally in one or two 

 similar kinds. 



One of the insects treated in this paper, the so-called peach 

 Lecanium, remains exposed upon the surface throughout its life, 

 secreting no scale. It has the appearance of a stationary lump-like 

 mass upon the bark, and may be easily crushed and detached. 



For the purposes of this economic discussion the scale insects 

 may be divided into two groups, according to their mode of hiber- 

 nation ; those which pass the winter as living, developed insects, 

 fully or partly grown, and those which winter in the egg. Of course, 

 the state or stage in which the winter is passed is the same as that 

 in which they go out in the nursery trade, and the fact that these 

 two groups require separate insecticide treatment makes it particu- 

 larly important that they should be clearly distinguished. The 

 developed insect can be readily and certainly killed by a thorough 

 fumigation process in which hydrocyanic acid gas is the destructive 

 agent. This insecticide has no effect on the egg, and bark-lice 

 which winter in the egg stage must be treated with a fluid insecti- 

 cide -commonly whale-oil soap or kerosene emulsion To make 

 this treatment certainly effective it must be applied to the insect 

 before the eggs are laid, preferably while it is still quite young. 



The most destructive nursery scales which hibernate as eggs 

 are the scurfy scale, the oyster-shell scale, the comtn )n elm scale, 

 and the rose or ra>«pberry scale, the last wintering in the egg to 

 the north and partly grown to the south. Those which hibernate 

 in a developed state are the Sin Jose scale, the Patnam scale, the 

 Forbes scale, the walnut scale, the peach Diaspis, the peach 

 Lecanium, and the rose scale in part, as just explained. 



