THE RELATION OF CLIMATE TO SPREAD. 33 



the actual conditions of infestation are perhaps as well known in this 

 State as in any other. In many localities the scale is held in check by 

 this careful system of inspection and by the prompt and thoro 

 adoption of the remedial treatment. 



CANADA. 



On the authority of Dr. James Fletcher, the Dominion entomolo- 

 gist, the San Jose scale infestation in the eastern portion of Canada is 

 confined to the Niagara Peninsula and counties along the north shore 

 of the west end of Lake Erie. It has also been found in several locali- 

 ties in British Columbia, having reached this province in its northward 

 migration along the Pacific slope. 



THE RELATION OF CLIMATE TO SPREAD. 



This subject was rather carefully considered in both Bulletins 3 and 

 12, in connection with the climatic districts or life zones established 

 by Dr. C. Hart Merriam, within which particular animals thrive 

 and outside of which they fail to establish themselves. These 

 life zones as thus limited have a special value in indicating the 

 probable spread of many injurious insects, and seem to be par- 

 ticularly significant in the case of the San Jose scale. These life zones 

 are: The tropical, occupying small areas in Florida and southern Texas; 

 the lower and upper austral, covering the bulk of the United States; 

 and the transition zone, coming between the last and the boreal zone 

 of Canada northward. These zones wdll be better understood by refer- 

 ence to the accompanying map (PI. V). The early records led to the 

 belief that the San Jose scale would be practically limited to the upper 

 and lower austral zones, and that the important fruit districts in the 

 northern United States and in elevated mountain regions, represented 

 b}^ the transition zone, would be slightly if any infested. In the main, 

 the records of the distribution of the San Jose scale have confirmed 

 this belief. Nevertheless, the scale has, in a number of instances, 

 appeared well into the transition zone as fixt by Doctor Merriam, 

 notably in Massachusetts, in New York, in Michigan, and a few other 

 points; but in most of these cases the evidence gained from the rela- 

 tion of other animals and plants would indicate that the transition and 

 upper austral zones were not correctly charted, so that in general the 

 belief in the immunity of the transition zone holds. 



As pointed out by Doctor Howard in Bulletin 12, the coastal law 

 which brings about the intermingling of northern and southern forms 

 will probably justif}^ the eastern Massachusetts occurrences. Other 

 occurrences in Massachusetts are justified by the river-valley law in 

 relation to the Connecticut River, and Doctor Merriam admits that his 

 line across the southern peninsula of Michigan is not very accurately 



