80 



belongs the oyster shell back louse of the apple and other trees 

 which has long been known as Aspidiotiis conchifonnis^ but Dr. 

 Riley has removed it from this species and redescribed it as My- 

 tillaspis pomi'cortic/s^ Riley, while he retains the old specific 

 name for the bark louse of the elm which thus remains Mytilaspis 

 conchifortnis^ Gmel. It however, certainly resembles very closely 

 the apple scale both in habits and appearance. 



THE ELM BARK LOUSE 



has long been known in Europe, and was doubtless brought to 

 this country on imported elms, and has not, at least so far as 

 I know, increased to such an extent as to be seriously injurious to 

 the American elm, on which, however, it sometimes occurs in 

 considerable numbers. In this species both males and females are 

 covered by a scale soon after they are hatched, though the females 

 far outnumber the males. The female scales are familiar to all, 

 and in this species the male scales are not very different. If in 

 the winter or early spring the scales are examined, they will often 

 be found to cover what appears like a yellow or reddish dust, but 

 which is really a mass of eggs. These eggs hatch in the spring or 

 early summer, into minute, active larvae, which soon leave the 

 protecting scale and run over the tree. At this time their form is 

 oval, and they may be not more than ,^50 inch long, so that they 

 are only just discernible by the unaided eye. They have the usual 

 beak of this class of insects, and this they thrust into the bark, and 

 begin to pump up the sap. The insect is soon attached by its 

 beak, and after this does not move about. Ere long, delicate 

 white threads are produced, and later, a continuous covering which 

 becomes the scale. The form changes, and the insect is soon very 

 different from what it was when first hatched, and on the whole, 

 it appears to be less highly organized, if the insect be a female. 

 After the impregnation the eggs develop in the body in great num- 

 ber, and these, when mature, are deposited under the scale. The 

 male develops differently, and is, apparently at least, more highly 

 organized than the female. He is furnished during a part of his 

 life with a gauzy, transparent pair of wings, the hind wings being 

 developed only into little hooks. After laying the eggs the female 

 perishes, and during the winter only eggs are found in the scale. 

 The perfect males have no proboscis or mouth parts, as the female 

 has, but by a most singular transformation the mouth parts arc 



