33 OYSTEE-SHELL BARK-LOUSE, 



it is difficult to conceive how they could have hecouie 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 Red Romanite, the Red Astracan, the Ram- 

 bo, the Early Harvest, the Summer Rose, and several varieties of 

 sweet apples. Some of those most free from the insect, are the 

 Northern Spy, the Maiden's Blush, the Beuona, 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 Ckalcididw. The amount of destruction 

 caused by the Chalcides can always be determined with mathe- 

 mathical certainty ; because we can either find the magrgots 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. \^j 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- 



