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altitude with the computed date as a constant. Thus from the 

 date of a periodical event or practice at an established base in any 

 given season a corresponding date constant of the event for any other 

 place within the range of the species or periodical practice involved, 

 may be estimated by means of the time constants of the law and their 

 equivalents in latitude, longitude and altitude. The possible 

 geographical range in which the species under its other environmental 

 requirements would survive and thrive might be similarly determined. 



With regard to the application of this law to economic entomology 

 the following species are dealt with. 



The most destructive enemy of southern pine timber is the southern 

 pine beetle, Dendroctonus frontalis, Zimm., the normal distribution 

 of which corresponds to that of the long-leaf and loblolly pines and 

 the greater part of the range of the short-leaf eastern yellow pine 

 south of Virginia and West Virginia. Under favourable climatic 

 conditions it may extend and become temporarily established in the 

 spruce areas of North CaroUna, West Virginia and the pine areas of 

 southern Pennsylvania. In the northern and highest limits of 

 distribution two complete generations occur annually, but in the 

 more southern regions as many as 5 or more generations occur with 

 a most complex overlapping of the broods of several generations 

 from the late spring to the early autumn months. Remedial measures 

 must be carried out during the period beginning at the end of the 

 flight of the beetles in the autumn and ending before flight begins 

 in the spring. This will vary according to latitude and altitude, 

 beginning in September in the north and higher altitudes and farther 

 south towards sea-level in December, and ending from February along 

 the Gulf coast to the middle of May at the northern or highest limit. 

 Knowing the location of an infested area, the beginning and ending 

 of control operations may be recommended through the application 

 of the bioclimatic law without preliminary investigation. 



The distribution of Dendroctonus brevicomis, Lee. (western pine 

 beetle) throughout the Pacific Slope and the .drainage area of the 

 Columbia River eastward to central Montana and Wyoming, south- 

 ward into Utah and Nevada and northward into British Columbia., 

 is represented by the latitude and altitude range of its food-plant, 

 the western yellow pine, Pinus ponderosa. Towards the highest 

 altitude limits one complete and a partial second generation occur; 

 the latter may be completed at lower altitudes. Remedial measures 

 should be applied as for D. frontalis, beginning at the end of the flight 

 season in the autumn and ending in the spring before general flight 

 begins. As the lower altitude limit of the western yellow pine rises 

 southward at the general average rate of about 400 feet to each degree 

 of latitude, the influence of latitude is balanced by the influence of 

 altitude, and the application of the law to the determination of the 

 time constants for different localities relates almost entirely to the 

 variation in altitude. The variation in the time for the beginning 

 and ending of the critical period of control between the lowest and 

 highest altitude limits in any latitude is 30 to 40 days or more. That 

 this species is extremely sensitive to local influences aflecting the 

 temperature is evident from the results of an experiment which shows 

 that larvae placed on the south side of a tree developed into pupae 

 in 20 days, the first adult emerging 35 days before those placed 



