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32 
it is difficult to conceive how they could have become so diversely 
affected, without supposing some selective taste or instinct on the 
part of the insects. 
I have made some inquiries with the view of determining what 
varieties of apple tree are most infested by these insects, and 
what varieties are most free from them. There are some kinds 
about which the testimony is pretty uniform, whilst, as might be 
expected, some occupy a middle or debatable ground. Some of 
the varieties most largely infested are the Janette, the Yellow 
Bell-flower, the large Bed Bomanite, the Bed Astracan, the Sam¬ 
bo, the Early Harvest, the Summer Bose, and several varieties of 
sweet apples. Some of those most free from the insect, are the 
Northern Spy, the Maiden’s Blush, the Benona, the Soulard Ap¬ 
ple, the Willow Twig, the Lowell and the Limber Twig, though 
with regard to the two last the testimony is conflicting. 
The last of the questions propounded at the commencement of 
this article, was whether the Oyster-shell Bark-louse is at the pre¬ 
sent time increasing or decreasing in numbers. Happily for the 
prospects of the apple culturist, the uniform answer to this ques¬ 
tion from all quarters, at least from all those parts of the country 
where these destructive insects have most largely prevailed, is 
that their numbers are rapidly diminishing. This result has not 
been brought about by human agency, but by a reaction on the 
part of nature itself, whereby the excessive prevalence of this in¬ 
sect has been followed by a corresponding increase of its natural 
enemies, until these last have come vastly to preponderate, so 
that the notorious Bark-louse of the apple tree seems to be in a 
course of rapid extinction. The chief of these destroyers of the 
bark-lice are the Aoari, or mites, and certain little roundish, foot¬ 
less maggots, which are the larvae of little four-winged flies be¬ 
longing to the family of Chalcididce. The amount of destruction 
caused by the Chalcides can always be determined with mathe- 
mathical certainty; because we can either find the maggots under 
the scales, (except when they are very young and therefore not 
easily discoverable,) or we can see the little round holes through 
which the flies have emerged. By counting these and then com¬ 
paring them with the whole number of scales on a given twig, we 
can estimate precisely the proportional number which the Chalci¬ 
des have destroyed. But the work of the Acari cannot be so ac- 
