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spondence with the Secretary of the Board. In neither of these cases 
should we expect the predaceous or parasitic forms to subdue their 
hosts more effectually in America than they do in Europe, except in so 
far as they were relieved, in the introduction into America, of whatever 
enemies they possessed in their native home. 
There are two other laws which it is worth while to consider in this 
connection. One is, that while a plant-feeder's natural enemies are i pt 
to cause its excessive abundance to be followed by a corresponding 
decrease, yet this alternation of excessive abundance and excessive 
scarcity will often be produced irrespective of such natural checks. An 
injurious insect which has been on the destructive march for a period 
of years will often come to a sudden halt, and a period of relative, and 
sometimes complete, immunity from injury will follow. This may result 
from climatic conditions, but more often it is a consequence of disease, 
debility, and want of proper nutrition, which are necessary corollaries 
of undue multiplication. Frequently, therefore, it may be inaccurate 
and misleading to attribute the disappearance of a particular injurious 
species to some parasitic or predaceous species which has been let 
loose upon it, and nothing but the most accurate observation will 
determine the truth in such cases. The past year furnished a A r ery 
graphic illustration in point. Throughout Virginia and West Virginia, 
where the spruce pines have for some years suffered so severely from 
the destructive work of Dendroctonus frontalis, not a single living 
specimen of the beetle has been found during the present year. This 
has been observed by every one who has investigated the subject, and 
particularly by several correspondents who have written to me ; by Mr. 
E. A. Schwarz, who was commissioned to investigate the facts, and by 
Mr. Hopkins, who has made the study of the subject a specialty. 
The clearest explanation of this sudden change is that the species 
was practically killed out by the exceptionally severe cold of last 
winter, since such was the case with several other insects. Now, fol- 
lowing so closely on the introduction by Mr. Hopkins of Clerus formi- 
carius, how easy it would have been to attribute the sudden decrease 
to the work of the introduced Clerus had not the decrease been so 
general and extensive as absolutely to preclude any such possibility. 
In like manner a certain Scale Insect (Aspidiotus tenebricosus) had 
become exceedingly destructive to the Soft Maples in the city of Wash- 
ington last year, whereas the present year it is almost entirely killed 
off, evidently by the same exceptional cold. Many of the affected 
trees were painted with whitewash, with a view of destroying the 
Aspidiotus, and the death of this last might have been attributed to 
the treatment (and naturally would be by those employing it) were it 
not that the same result was equally noticeable on the trees not 
treated. Reports from southern California would indicate that the Red 
Scale (Aspidiotus aurantii) is, in many orchards, losing its destructive, 
ness through agencies other than its insect enemies, and in this case 
the facts are particularly interesting because of the ease with which 
