AFFECTING THE BRANCHES. 



Fig. 5. 



4. The Oyster-shell Bark-Louse (Aspidiotus conchiformis 

 "Gmelin). — Although there are two species of Bark-lice that affect the 

 apple in the northern United States, there is only one, so far as we are 

 aware, that is injurious in Canada. The other, which is called Harris's 

 Bark-louse (A. Harrisii, Walsh,) is often very destructive in Pennsyl- 

 vania, Maryland, South Illinois and Missouri, and is occasionally met 

 with further north. We are not very likely to be troubled with it in 

 this country, but yet it is well that we should know the difference 

 between it and the other more common species. " The color of the 

 scale is dirty white, and its form is irregular, being usually egg-shaped ; 

 but however variable in outline, it is always quite flat and causes the 

 infested tree to wear the appearance shown in the accompanying wood- 

 cut (Fig. 5); while the minute eggs which are found under it in winter 

 time are invariably blood- red or lake red." — (Riley.) 



The other species, which infests our apple-trees in all parts of the 

 Dominion, is named the Oyster-shell Bark-louse (A. conchiformis, 

 Gmelin), from the shape of the scale, which is always like that of the 

 oyster-shell ; it is of an ashen-gray color, the same hue as that of 

 the bark, and in winter and early spring covers a number of white eggs — not red as 

 in the preceding species. The shape of the scale and the color of the eggs form ready 

 and apparent distinctions between the two species, so that there is no danger of mistaking 

 them. A comparison of Fig. 6, which represents a twig covered with the 

 Oyster-shell Bark-louse, with Fig. 5, representing the other species, will show 

 the reader the distinction more satisfactorily than any words of ours. Our 

 Canadian species (which, by the way, like so many others of our most injuri 

 ous insects, is an importation from Europe,) passes its life in the following man- , 

 ner : — About the end of August or beginning of September the mother insect j 

 lays a quantity of very minute eggs beneath a scale that she has already formed 

 in some, as yet, unaccountable way ; some entomologists incorrectly say that 

 this scale is the body of the gravid female covering and protecting the eggs ; 

 others, with more probability, that it is an exudation from her body. Having \ 

 completed this work, she dies ; but the eggs remain under the scale, which, as 

 we have seen, very much resembles an oyster-shell in shape, all through the i 

 winter until the following spring. About the first week in June, or later, ac-' 

 cording to the season, the eggs hatch and produce a number of excessively 

 small plant-lice (Fig. 7-2) which, on the first subsequent hot day, leave the 

 protection of the scale, and spread over the branches of the tree, attacking especi- 

 ally the soft terminal twigs. For a few days they possess the power of moving -pj^ 3 

 about, but after they once select a spot on the tree and begin to suck the sap 

 there, they never move again, but remain as stationary and as much fixtures as if they 



Fig. 7. 



were twigs themselves. After a time each one becomes covered with a white waxy secre- 

 tion, that issues from the body in the shape of very fine delicate threads (Fig. 7-3). This 



